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WATER CHEMISTRY
GUIDELINES FOR
HIGH PRESSURE BOILERS
PUB.NO. 2003
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CONTENTS
1.0 GENERAL
1.1 MAKE - UP WATER TREATMENT
1.2 INTERNAL CORROSION
1.3 EFFECT OF pH
1.4 EFFECT OF OXYGEN
1.5 BOILER WATER TREATMENT
1.6 CONDENSER LEAKAGE
FIG.1 RELATIVE CORROSION RATE OF CARBON STEEL VS pH
FIG.2 SILICA VS DRUM PRESSURE
FIG. 3 SILICA IN BOILER WATER VS DRUM PRESSURE
FIG. 4 OPERATION BETWEEN 70 - 125 kg/cm2
FIG. 5 OPERATION BETWEEN 126 - 165 kg/cm2
FIG. 6 OPERATION BETWEEN 166 - 182 kg/cm2
FIG. 7 OPERATION BETWEEN 183 - 203 kg/cm2
RECOMMENDED FEED WATER LIMITS
BOILER WATER LIMITS
GUIDELINES FOR EMERGENCY OPERATIONS
HOT WELL CONDITIONS FOR ALL VOLATILE TREATMENT
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WATER TREATMENT
1.0 GENERAL
High pressure boiler (operating above 60 kg/cm2 ) design needs a close look at the limiting
conditions like heat transfer, heat exchanger metal temperature,circulation etc., The entire
exercise of Water Treatment (both internal and external treatments) is aimed at (1) corrosion
control and (2) steam quality. The cost of corrosion and deposition to electric utilities is veryhigh due to repairs and loss of production (shutdowns).Poor steam quality leads to deposition
on turbine blades causing efficiency loss and failures .Thus the successful operation of high
pressure boilers and turbine units require a strict vigil on the Water Treatment practices and
controls, particularly for high pressure drum type and once through boilers.
1.1 MAKE - UP WATER TREATMENT
Trouble free continuous operations of high pressure boilers call for very stringent feed water
quality. Total solids and silica, other than corrosion products,being the main constituents are
responsible for carry-over and deposition reducing the units efficiency. Make up water isrequired to becontrolled and maintained at low levels. Silica in particular, is CARRIEDOVER
in the form of VAPOUR at high pressures, needs to be controlled at low levels.Feed water is
used for de-superheating spray and any contamination of feed water (either from steam
condensate or from make up water) directly enters the superheated steam . IMPURE FEED
WATER increases BLOW DOWN making the operation un-economical.Hence feed water is
required to be very pure for high pressure boilers. This inturn necessitates high purity
make up water, other than polishing the steam condensate, wherever applicable. Modern
demineralisation plants with different combinations of ion-exchangers, are capable of producing
the requiredquality of make up water with specific electrical conductivity less than 0.2 micro
mhos/cm and silica 0.02/0.01 ppm.
1.2 INTERNAL CORROSION
Corrosion is a common phenomenon in high pressure boilers. Corrosion in boiler circuits as
well as in pre-boiler circuits can cause tube failures followed by force shut down of boilers.
The causes of corrosion are,
i. pH ( acidity or high alkalinity )ii. Oxygen
iii. Excessive ammonia (on copper base alloys )
iv. Concentration of alkalising agents due to localised over heating
v. Poor quality of passivating layer or breaking of passivating layer due to thermal
shocks
vi. Decomposition of organics into corrosive products.
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1.3 EFFECT OF pH
The reaction of feed water on steel is spontaneous and rapid at high temperatures. The only
reason that boiler steel can survive normal operating conditions is that the passivated layer of
magnetite ( Fe3O
4) / hydrated iron oxide (FeOOH) forms a protective layer on the steel surface,
preventing corrosion. The whole exerciseof maintaining alkalinity control is to maintain an
environment in which the oxide film is stable and protective. One of the objectives of Water
Treatment in boilers is to protect this film against the aggressive action of impurities introducedinto the boiler with the feed water.
The work of Bell and Van Track has been used to relate the relative corrosion of steel over a
range of pH values. It was found that the protective layer is getting dissolved at pH values
below 5.0 and above 13.0 Minimum corrosion is indicated at pH of 9.0 to 11.0 (Fig. 1)
Although corrosion is low over a wide band of pH values, unfortunately, corrosion occurs by
localised concentration of alkaline chemicals on tube metal due to starvation, localised over
heating etc. Rather than the concentrations existing in the bulk boiler water. Local concentration
changes the pH drastically and corrosion takes place. Due to limitations of chemicals used, an
optimum pH of 8.8 to 9.2 is recommended for feed water, which can be achieved by use of notmore than 0.5 pprn of ammonia. Any excess presence of ammonia (indicated by higher pH
values) will cause copper corrosion in the pre-boiler system.
Another parameter which affects corrosion rate is the temperature inside the reaction vessel.
Hence different temperature ranges or the pressure ranges call for different pH values to be
maintained in order to minimize corrosion.
Accordingly boiler water pH requirements are higher than the feed water limits and different
for different pressure ranges. Boiler water pH is elevated to the recommended levels using
Trisodium phosphate. The use of caustic soda is not recommended for this purpose as it hasthe danger of concentration and destruction of protective oxide film to cause corrosion.
1.4 EFFECT OF OXYGEN
The exclusion of oxygen in feed water is essential to avoid corrosion. Small quantities of
dissolved oxygen are capable of causing severe corrosion pitting in boiler tubes. A combination
of poor oxygen control and chlorides in boiler water can result in serious hydrogen damage
type corrosion of water wall tubes. Power plants employee tight cycles to prevent oxygen
infiltration and condenser leakage are generally free from corrosion problems. Continuous
monitoring of oxygen is required in high pressure system.
Too often, oxygen enters the system undetected during periods of operation which are poorly
monitored. Poor start-up procedures are also responsible for oxygen ingress. A most common
error is the use of undeaerated water. Feed water at a temperature less than 100 deg. C contains
excessive quantities of dissolved oxygen and hence feed water should never be allowed into
the boiler at any time below this temperature.Deaerator is the main equipment to control
oxygen within 0.01 - 0.02 ppm.
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The best deaeration is obtained in units which operate above atmospheric pressure at all load
conditions. A normal contamination of feed water occurs, when the deaerator pressure varies
with a turbine bleed stage from above atmospheric to vacuum at low loads. Heater drips from
low pressure system contain varied quantities of oxygen. A significant oxygen increase occurs
in the heater drips as a heater drops below atmospheric pressure at low loads. A major problem
of oxygen leakage occurs at low loads when heater drips are pumped directly to the condensate
system. It is preferable to exhaust the drains to the deaerating section of the condenser.
The most serious corrosion occurs in boilers which shut-down and start-up frequently withoutincorporation of technique to minimise oxygen in the feed water. Much of the problems can
be reduced by pressurising the deaerator with steam at about 0.5 kg/cm2 (g) to exclude oxygen
from the water during any short outage. For long outages, the vapour and water contacted
surfaces of the feed water system should be pressurised with steam or nitrogen.
With the main oxygen removal by deaeration, residual oxygen in small quantities can be
reduced further by reducing agents such as sodium sulphite or hydrazine.Hydrazine being a
volatile chemical, should only be used for high pressure boilers. Hydrazine reacts with oxygen
to form nitrogen and water. This reaction is very low at temperatures below 175o C. Above
230o C, Hydrazine is decomposed rapidly to nitrogen, hydrogen and ammonia. Hence hydrazine
dozing alone cannot control oxygen without effective deaeration. Since hydrazine has also
the property of passivating the metal surfaces of the pre-boiler cycle by reducing the oxidised
form of iron and copper, it is advantageous to add hydrazine to the cycle at the outlet of the
condensate pump.
1.5 BOILER WATER TREATMENT
It is recommended to use co-ordinated phosphate - pH treatment ( Sodium to phosphate
ratio = 3) method for high treatment excludes free caustic from the boiler water. Caustic
present in boiler results in a ductile-gouging type corrosion. Even if bulk boiler water does
not contain large amount of free caustic, there is great potential for caustic to concentrate andcause corrosion. Internal metal oxide deposits provide sites for concentration. As steam is
produced, dissolved solids concentrate in the thin film between tube wall and bulk fluid. Low
sloped tubes permit concentration. It has been well established that phosphate even concentrated
under hide-out conditions is not aggressive to the tube metal.
Congruent phosphate program (Sodium to phosphate ratio = 2.6) takes care of both caustic
and acid corrosion but control of sodium to phosphate ratio is difficult, calling for continuous
feed and blow down.
Figs. 4 to 7 provide guidelines to use either of the programmes, subject to the operators
convenience.
Volatile treatment is another method of treatment but it is primarily to control corrosion of
heater surfaces in the pre - boiler circuit. Chemicals such as ammonia, cyclohexylamine and
morpholine are volatile at high pressure boiler water temperatures. As a result there is no
significant buffering of boiler water pH due to these chemicals. Any ingress of condenser
leakage contaminants requires the immediate addition of phosphate to prevent the depression
of pH and the incidence of hydrogen damage. The main attraction of volatile treatment is that
it assures good steam purity .
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Impurities due to vaporization of salts and mechanical carry-over are at a minimum.But it is
necessary to employ condensate polishing and have reliable instrumentation for detecting
immediately any condenser leak to safety operate with volatile treatment.
1.6 CONDENSER LEAKAGE
Condenser leakage, as mentioned earlier, is a major source for corrosion. The type of cooling
water and its interaction with boiler water determines whether b oiler water pH will become
more acidic or alkaline during a period of condenser leakage. It is very important to preventcondenser leakage of sea water as it results in acidic boiler water. The hardness chloride salts
present abundantly in sea water generate hydrochloric acids at boiler water temperatures.
Uncontrolled large leakages of sea water can cause within hours extensive corrosion (hydrogen
damage) of water wall tubes. There should be no hesitation to shutdown and save the unit if
boiler water specifications,as recommended cannot be maintained during the condenser leakage.
Any unit should have an on-line instrument with a cation column at the outlet of condenser to
monitor conductivity continuously and detect immediately any condenser leakage.
FIG.1 RELATIVE CORROSION RATE OF CARBON STEEL VS pH
FIG.2 SILICA VS DRUM PRESSURE
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FIG. 3 SILICA IN BOILER WATER VS DRUM PRESSURE
FIG. 4 OPERATION BETWEEN 70 - 125 kg/cm2
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FIG. 5 OPERATION BETWEEN 126 - 165 kg/cm2
FIG. 6 OPERATION BETWEEN 166 - 182 kg/cm2
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FIG. 7 OPERATION BETWEEN 183 - 203 kg/cm2
RECOMMENDED FEED WATER LIMITS
DRUM OPERATING PRESSURE
Kg/cm2 (g)
61-100 100 and above
ONCE
THROUGH
BOILERS
TREATMENT TYPE P04 P04 AVT AVT
1. Hardness ppm (max) NIL NIL NIL NIL
2. pH at 250C 8.8-9.2 8.8-9.2 8.8-9.2 8.8-9.2
3. Sp. electrical conductivity after 0.50 0.30 0.20 0.20
cation in H+ form at 250C micromho s/cm (max)
4. Dissolved oxygen ppb (max) 5.0 5.0 5.0 5.0
5. Silica as SiO2 ppb (max) 20.0 20/10* 10 10
6. Iron as Fe ppb (max) 10 5 10 10
7. Copper as Cu ppb (max) 10 5/3* 3 3
8. Residual Hydrazene ppb 10-20. 10-20 10-20 10-20
* Should match with the corresponding values to be maintained in super heated steam
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BOILER WATER LIMITS
(FOR DRUM TYPE BOILERS NORMAL OPERATION)
DRUM OPERATINGPRESSURES Kg/cm2 (g)
61 90 91 125 125 165 165 180 181 & above
TREATMENT TYPE PO4 PO4 PO4 PO4 AVT PO4 AVT
1. Total Dissolved solids
ppm (max )
100 100 50 15
(Note)
2.0 10
(Note)
1.0
2. Sp. Electrical conductivitymicro. mhos/ cm (max)
200 200 100 30(Note)
4.0 20 2.0
3. Silica as Sio2 ppm (max) 4.0 To becontrolled as
per fig .2&3
0.20 0.10 0.10 0.10 0.10
4. Chlorides ppm (max) - - - 0.6 0.02 0.50 0.01
5. pH at 25o C 9.0-- 9.0-- 9.1-- 9.1-- 9.3-- 9.1-- 9.3--
10.0 10.0 9.8 9.7 9.5 9.7 9.5
6 . Phosphate , res idual ppm 5 20 5 20 5 20 2 6 N/A 2 6 N/A
* NOTE : Total solids 15 & 10 ppm correspond to 10 ppb sodium steam
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S I . N o
.
P r e s s u r e
r a n g e
k g / s q -
c . m ( g )
H o t w e l l s o l i d s
p p m
O p e r a t i o n a l
L i m i t a t i o n s
C o n t r o l
L i m i t s
B o i l e r
W a t e r
C o n t r o l
0 1 6 1 -1 2 5 0 . 5 - . 2 . 0
( A B N O R M A L )
> 2 . 0( E X C E S S I V E )
L i m i t e d
o p e r a t i o nN o t e . 1
E m e r g e n c yo pe r a t i o n -
N o t e . 3
T D S < 2 0 0
p p r np H 9 . 1 - 1 0 . 1
P 0 4 5 -4 0 p p m
- D O -
N O T E 2
N O T E 4
0 2 . 1 2 6 -1 6 5 0 . 5 -2 . 0
( A B N O R M A L )
> 2 . 0
( E X C E S S I V E )
L i m i t e d
o p e r a t i o n
N o t e . I
E m e r g e n c y
o pe r a t i o n -
N o t e . 3
T D S < 1 0 0 p p m
p H 9 . 1 - 1 0 . 1
P 0 4 5 - 2 0 p p r n
- D O -
N O T E 2
N O T E 4
0 3 . 1 6 6 -1 8 0 0 . 2 5 -1 . 0
( A B N O R M A L )
> 1 . 0( E X C E S S i V E )
L i m i t e d
o p e r a t i o nN o t e . 1
E m e r g e n c yo p e r a t i o n
N o t e . 3
T D S < 5 0 p p m
p H 9 . 1 - 1 0 . 1P 0 4 5 - 2 0 0 ' pr n
- D O -
N O T E 2
N O T E 4
0 4 . 1 8 1 -2 0 3 0 . 1 -1 . 0
( A B N O R M A L )
> 1 . 0
( E X C E S S I V E )
L i m i t e d
O p e r a t i o n -
N o t e 1
E m e r g e n c y
o pe r a t i o n -N o t e . 3
T D S < 5 0 p p m
p H 9 . 1 - 1 0 . 1
P 0 4 5 - 2 0P P M
- D O -
N O T E 2
N O T E 4
GUIDELINES FOR EMERGENCY OPERATIONS
(DRUM TYPE - PHOSPHATE TREATMENT)
NOTE 1: Schedule Inspection and repair of condenser as soon as possible
NOTE 2: Immediately start chemical injection to achieve higher phosphate and pH condition
not continue operation if pH cannot be maintained above 8 total solids below specified
limits. Avoid use of desuper heating spray.
NOTE 3: Immediately reduce load to permit isolation of damaged condenser and prepare for
orderly shutdown if hot well TDS cannot be re duced quickly below specified limits.
NOTE 4: Prepare for wet lay up of the boiler
NOTE 5: Control silica in boiler water in accordance with graph provided.
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GENERAL INSTRUCTIONS
1 . All Feed water measurements shall be made at high pressure heater outlet or economiser inlet
.
2. Oxygen can also be additinrially measured at deaerator outlet to determine the quantity of
N2H
4dozing .
3. The recommended pH in feed water can be obtained by dozing ammonia, morpholine or any
volatile amine. The concentration of volatile chemical in the feed water should not exceed
0.5 ppm.(expressed as Ammonia)
4. The phosphate and pH are recommended in accordance with co-ordinated phosphate curves
(Figs. 4 to 7) to prevent presence of free hydroxide in boiler water.
5. Water levels in drum should be maintained within limits during all operational modes, start-up,
load fluctuation and normal operation.
6. The allignment of drum internals should be checked and ensured to be in order atleast once
every year
7. It is needless to emphasize that correct sampling, accurate measurements with the use of
reliable instruments at adequate intervals and proper logging of readings go a long way in
ensuring trouble free operation.
HOT WELL SOLIDS (PPM)PRESSURE RANGE
(Kg/sq.cm) NORMAL
OPERATION
EMERGENCY
OPERATION
126-165 < 0.05 < 0.1 PPM
Above 166 < 0.05 < 0.25 PPM
Note: Switch over to phosphate treatment when hot well solids exceed emergency operation
levels.
HOT WELL CONDITIONS FOR ALL VOLATILE TREATMENT
(FOR DRUM TYPE BOILERS)
Go To Pub Index
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1 PUB.NO. 2019
METHODS OF WATER
ANALYSIS
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CONTENTS
1. GENERAL INSTRUCTIONS ON SAMPLE COLLECTION AND USE OF
INSTRUMENTS
2. DETERMINATION OF TOTAL HARDNESS
3. DETERMINATION OF CARBON-DI-OXIDE
4. DETERMINATION OF P&M ALKALINITY
5. DETERMINATION OF FREE ALKALINITY IN BOILER WATER
(STRONTIUM CHLORIDE METHOD)
6. DETERMINATION OF SULPHITE
FIG.1 METHOD OF COLLECTING SAMPLE FOR OXYGEN
FIG.2 WINKLER FLASK FOR DISSOLVED OXYGEN DETERMINATION
7. DETERMINATION OF DISSOLVED OXYGEN (MORE THAN 0.10 PPM)
8. DETERMINATION OF PERMANGANATE NUMBER (DETERMINING
ORGANIC SUBSTANCES : POTASSIUM PERMANGANATE CONSUMPTION)
9. DETERMINATION OF EVAPORATION (T.D.S) IGNITION RESIDUES AND
VOLATILE MATTER
10. DETERMINATION OF OIL (FLUOROCARBON MATTERS)
11. DETERMINATION OF pH-VALUE
12. DETERMINATION OF CONDUCTIVITY (CONDUCTO BRIDGE METHOD)
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FIG.3 HYDROGEN ION EXCHANGER OF PLASTIC FOR MEASURING
CONDUCTIVITY
13. DETERMINATION OF DISSOLVED OXYGEN
14. DETERMINATION OF SOLUBLE SILICA
15. DETERMINATION OF TOTAL SILICA
16. DETERMINATION OF ORTHOPHOSPHATE
17. DETERMINATION OF IRON - BATHO PENANTHROLINE METHOD
18. DETERMINATION OF COPPER NEOCUPROINE METHOD
19. DETERMINATION OF AMMONIA
20. DETERMINATION OF HYDRAZINE
21. DETERMINATION OF CHLORIDE (COLORIMETRIC METHOD)
22. DETERMINATION OF MORPHOLINE
23. DETERMINATION OF CYCLOHEXYLAMINE
24. DETERMINATION OF SODIUM (FLAME PHOTOMETER)
25. DETERMINATION OF SODIUM-LOW LEVEL (ONLINE METHOD)
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INTRODUCTION
The operation of modem steam generating plant necessitates constant supervision of water and steam
conditions. For effective supervision, examination of water and steam samples is essential to provide
suitable data for those responsible for operating water treatment plant and steam generating units to
enable them to form a picture of the general operational state.These data should also help to give timelywarning of any changes to enable corrective measures to be taken before trouble or damage ensues.
Collection of representative sample and use of correct method of measurement are vital to obtain
accurate results. The frequency of sampling and analysis depends on the maximum time during which
lack of knowledge of the concentration of contaminants or additives, is acceptable. Local conditions
such as plant design, condenser leakage, blow down and startup will often dictate the sampling frequency.
In order to that the measurement of a contaminant or additive can be capable of detecting the smallest
significant deviation from a set standard, the precision of analytical results must not exceed given values.
Therefore, analyst must make regular checks to ensure that the precision remains satisfactory; a statistical
assessment of results is necessary.
Auto - analysers are of benefit, as they give a better overall picture and reveal trends towards change.
All automatic analytical instrumentations should be maintained in an operational and calibrated status.
If chemical auto-analysers are not operational, greater emphasis must be placed on laboratory analyses.
In general, major operational decision will be made on the results of these measurements to achieve
optimum plant operation; in other words, the longest possible service life for the plant with minimum
operational losses and consumption of chemicals.
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1. GENERAL INSTRUCTIONS ON SAMPLE COLLECTION AND USE
OF INSTRUMENTS
1.1. SAMPLE COLLECTION - PRECAUTIONS
In the conditioning of industrial water it is necessary that analyses be made to govern the treatment
processes. If the results obtain from a analysis are to be of any value, it is necessary to get a
sample that if freely representative of the condition of the water at the point at which the sample
has been collected.
Sampling lines are to be kept continuously flowing. Sampling and cooling water line should be
free from choking and sampling lines to be purged for about 30 minutes every day as a routine
and whenever choking is suspected. To avoid contamination of cooled samples they are to be
collected in dust-free atmosphere. Cooling water contamination of samples is to be prevented.
The sampling rate should be not less than 450 ml / min and sample temperature shall not exceed
about 40 degree C. The container used for collecting samples should be made of polythene with
innercap. Before collecting samples, rinse the container atleast 3 times. After collecting the samples,
rinse the stopper and tightly close the container.
1.2 USE OF INSTRUMENTS - GENERAL INSTRUCTIONS
i) Spectrophotometer :
The following instructions shall be followed to ensure the accuracy of Spectrophotometric determinations.
a) The Spectrophotometer used for colorimetric determinations is to be calibrated atleast once in
six months.
b) The temperatures of both sample solution and calibration solution shall be nearly equal preferablyabout 25 degree C.
c) Optically matched cells are to be used for calibration and measurement.
d) For the determinations of the various parameters, individual graphs are to be prepared with
standard solutions. The graphs are to be checked or redrawn if required during calibration checks.
e) The straight line portion of the curve which represents linearity only is to be used.
f) Solutions of higher concentrations are to be diluted suitably so that the concentration can bemeasured within the linear portion of the graph.
g) Suppliers operating instructions shall also be followed.
ii) Other Instruments :
The general operating instructions supplied along with instruments shall be followed.
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2. DETERMINATION OF TOTAL HARDNESS
2.1 INTRODUCTION
i) Total Hardness
Calcium and magnesium ions in water are sequestered by the addition of sodium ethylene
diamine tetra acetate. The end point of the reaction is detected by means of an indicator,
chrome-black T, at an optimum pH of 10.0-10.4 which has wine red colour in the presenceof calcium and magnesium, and a blue colour when they are sequestered.
ii) Calcium Hardness
Calcium ions in water are sequestered by the addition of EDTA. The end point of the
reaction is detected by means of an indicator, murexide which is dark purple in the
absence of calcium but with which calcium forms a light salmon red complex. The optimum
pH range is about 10.4
2.2 REAGENTS
i) Standard Calcium Chloride Solution
(1 ml equals 1 mg CaCO3)
Dissolve 1.0000 g of reagent grade calcium carbonate containing less than 0.04% Mg
(dry at 1100C for one hour) in 10 ml 1: 1 hydrochloric acid without spattering, dilute
exactly to one litre and transfer to a clean dry glass stoppered bottle for storage (or use a
commercially prepared standard.)
ii) Buffer Solution
350ml Ammonium hydroxide(conc.) + 54gms ammonium chloride + 20ml magnesium
complex solution are mixed and made upto one litre with distilled water.(Magnesium solution
is prepared as follows. 4.1 gm of MgO (analar) is mixed with 37.2 gms of EDTA and
dissolved in 410 ml of warmed distilled water.)
iii) Calcium indicator
Grind 0.2 gm of Ammonium purpurate(Murexide) with 100gms of Sodium chloride to
40 to 50 mesh size.
iv) Chrome Black T indicator
Grind 0.2gms of chrome black T powder with 80gms of powdered NaCl and store in a
dark coloured bottle.
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V) Standard EDTA Solution
Di-sodium dihydrogenethylene- diaminetetra-acetate of analytical reagent quality is dried
at 800C. Weigh 4.0 gm of the substance and dissolve it in 800 ml of demineralised water.
Adjust the pH to 10.5 with 5% NaOH solution. Pipette 25 ml of the standard Calcium
chloride solution (prepared above) into an Erlenmeyer flask (125 ml) . Add 1:4
Ammonia of Chrome-black T indicator.Titrate with the EDTA solution as per the procedure
given below (2.4). Let V be the volume of the standard EDTA solution required for thetitration.
Volume of EDTA to be taken up for dilution = V/25 x 1000.
The volume of EDTA solution as calculated above is taken in a 1000 ml. volumetric
standard flask. Dernineralised water is used to make up to the mark in the volumetric
flask. This EDTA solution corresponds to a value of 0.02N.
The solution is stored in polythene bottles and restandardised monthly.
Sodium hydroxide solution(4%)
Dissolve 4.0 gms of NaOH in water and dilute to 100ml.
2.3 GLASSWARES
Burette (0. 1 ml accuracy)
50ml measuring cylinder-1No.
White porcelain casserole with a glass stiffer.
2.4 PROCEDURE
i) Total Hardness
Pipette 50m l of the sample into a white porcelain casserole. If necessary adjust to
pH 7-10 by using ammonium hydroxide or HCL
Add 0.5ml of buffer solution and mix by stirring. (The pl-I of this solution should be
between 10- 10.2). Add approximately 0.2gms of dry chromeblack T indicator to produce
the required depth of colour. The titration with EDTA should proceed immediately uponaddition of the chrome blackT.
If hardness is present the solution will turn red. Standard EDTA solution is added slowly
with continuous stirring until the end point is reached which is pure blue colour with no
reddish tinge remaining. Further addition of EDTA will produce nofurther colour change.
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ii) Calcium Hardness
Pipette 50ml of the sample into a white porcelain casserole.
Add 2 ml of 4% NaOH solution and stir.(The pH of this solution should be above 10.4)
Add approximately 0.2gm of calcium(Murexide) indicator.
Add standard EDTA solution slowly with continuous stirring until the colour changes from
salmon pink to orchid purple.
iii) Calculation
Total Hardness (as ppm CaC03) = ml std EDTA soln x 20
Calcium hardness (as ppm CaC03) = ml std EDTA soln x 20
Magnesium hardness(as pprn CaC03) = Total hardness (as ppm CaC03) minus
calcium hardness (as ppm CaC03)
3. DETERMINATION OF CARBON -DI-OXIDE
3.1 INTRODUCTION
The carbon di-oxide content is the sole contributor to the acidity of the water. On this account,
the CO2 determination bears a close resemblance to the acidity titration. The differences reside
in the concentrations of the titrants and the fact tha t the titration is conducted in a manner thatminimizes the escape of the volatile CO2 gas.
3.2 REAGENTS
i) Boiled distilled water-This should be used in the preparation of all solutions.
ii) Phenolphthalein indicator solution.
iii) 0.02 N sodium carbonate solution.
(Prepare 0.1 N Na2CO
3solution by dissolving 5.3 g anhydrous Na
2CO
3in one litre of boiled
distilled water. This solution should be diluted suitably to get 0.02 N Na2CO3 solution)
3.3 EQUIPMENT
Glass flask with 100 cc and 200cc marks.
Burette-50cc capacity with 0. 1 ml marking
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3.4 ANALYSIS PROCEDURE
The water is run slowly for a long time through a hose reaching down to the bottom of the test
flask. After pouring-off excess water down to the 100 ml mark or 200 ml mark, the content of
free CO2 is determined at once on the spot. Add to the water I cc of phenolphthale in solution
and titrate with 0.02 N Na2CO3 Solution. After each fresh addition of Na2CO3 solution, the
flask is closed and turned upside down (Not shaken) before continuing. Titration is completedwhen the colour of the water stays weak pink for 5 minutes. In a second test the full quantity of
sodium carbonate solution needed is added at once, and if necessary a little more, until the pink
colour is retained for 5 minutes.
3.5 CALCULATION
CO2
milli-grams per litre = A x N x 22000 / ml.sample taken
Where A = milliliters of titrant used
N = normality of titrant
4. DETERMINATION OF P AND M ALKALINITY
4.1 THEORY OF TEST
This test is based on the determination of the alkaline content of a sample by titration with a
standard acid solution. In this measurement, the end-points are taken as points of change in the
colour of organic indicators; phenolophthalein (apporx.pH 8.3) and methyl orange(approx. pH
represent definite points to which the alkalinity of the sample has been reduced by the addition ofthe standard acid solution.
4.2 REAGENTS
i) Sulphuric acid, N/50
ii) Phenolphthalein Indicator
iii) Methyl orange indicator
iv) Methyl purple indicator
4.3 APPARATUS REQUIRED
1 Burette, 25ml or
1 Casserole, porcelain, 250ml
1 Cylinder, graduated, 50ml.
1 Stirring rod, glass.
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4.4 PROCEDURE FOR TEST
Measure a clear 50 ml sample of water in the graduate and transfer to the casserole. Add 4 or 5
drops of phenolphthalein indicator. If the sample is an alkaline water, such as usually is the case
with the boiler water, it will turn red. If the sample is a raw or natural water, it usually will remain
coloureless. Add the standard N/50 sulphuric acid from the burette drop by drop to the sample
in the casserole, stirring constantly until the point is reached where one drop removes t he last
trace of red colour and the sample becomes colourless. Stop and record the total number of mlto this point as the P reading.
Add 4 drops of methyl orange indicator (if no red colour develops on the addition of the
phenolphthalein indicator to the original sample, the titration may be started with the methyl
orange indicator at this point). Continue adding the acid drop by drop until one drop changes the
colour from a yellow to a salmon-pink., Record the final burette reading as the M reading. This
is a more difficult point and some practice may be required. The general tendency is to add too
much acid. If too much acid is added, the sample will change from a salmon-pink to a definite
red.Record the titration to the P point and the total titration to the M point as the P and M
readings respectively. (Note that the M Reading will always be greater than the P reading in as
much as the P reading is included in the M reading).
If the water sample is coloured, such as one containing chromate, methyl purple indicatormay be
substituted for methyl orange indicator to provide a more definite end-point. The color change
with methyl purple is from green to gray to purple. The end-point is taken as the first change to a
definite purple.
4.5 CALCULATION OF RESULTS
Formula:
ppm alkalinity as CaCO3 = ml N / 50 sulphuric acid x 1000 / ml.Sample
4.6 LIMITATIONS OF TEST
It is preferable to expresses the results of the alkalinity determination in terms of P and M
alkalinity as above.However, results are sometimes calculated in terms of bicarbonate, carbonate
and hydrate on the assumption that titration to the P end-point is equivalent to all the hydrate and
one half the carbonate alkalinity and that the titration to M is equivalent to the total alkalinity.
Many factors such as the presence of phosphate silica, organic and other buffers affect this
titration and the calculation of the form of alkalinity present may be in error. Under normal
circumstances in plant control, expression of results as P and M alkanity is entirely satisfactoryand is to be preferred from the standpoint of simplicity.
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4.7 ALKALINITY RELATIONSHIP
The following table summarises the relationship between P and M values and the concentration
of hydroxide, carbonate and bicarbonate.
5. DETERMINATION OF FREE ALKALINITY IN BOILER
WATER (STRONTIUM CHLORIDE METHOD)
5.1 INTRODUCTION
This method is based on the titration of the hydroxide ion with a standard acid to the
Phenolphthalein end-point after the carbonate and phosphate ions have been precipitated
with strontium chloride.
5.2 REAGENTS
i) Standard HCI solution 0.02 N
ii) Phenolphthalein indicator dissolve 0.5g of phenolphthalein in 100ml of 50% solutionof ethyl alcohol in water
iii) Strontium chloride solution = Dissolve 4.5g of strontium chloride in water
and dilute to a litre.
5.3 APPARATUS REQUIRED
50 ml - measuring cylinder
250 ml - Erlenmeyer flask with stopper
50 ml - burette-readability 0.1ml
ppm as CaCO3
Condition (OH) (OH - ) (CO3)(CO3-) (HCO3) (HCO3
-)
P=O O O M
2PM 2P-M 2(M-P) O
P=M M O O
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5.4 PROCEDURE
Pipette 50 ml of sample into 250 ml. Erlenmeyer Flask.
Add 25 ml of stroniurn chloride solution
Keep loosely the stopper of the flask and heat to boiling.
Remove flask and immediately push stopper tightly into flask.
Allow to cool and add 5 drops of phenolphthalein solution. The absence of colour indicates no
free hydroxide alkalinity.
If pink colour is present, titrate with 0.02 N hydrochloric acid to a colourless end-point.
5.5 CALCULATION
Free alkalinity = (N) x (V) x 17,000 / ml sample
as ppm (OH)
Where, V = ml of HCI and N = Normality of HCl
5.6 INTERFERENCES
Chromates and Silicates
Method takes care of phosphates, carbonates and most ammonia.
6. DETERMINATION OF SULPHITE
6.1 INTRODUCTION
This method is designed primarily for the routine control of boiler feed waters subjects to sulphate
treatment. Reductants like sulphide and certain heavy metal ions react similarly to sulphite. Copper
catalyzes the oxidation of sulphite on exposure to air, especially at high temperatures.
6.2 REAGENTS
i) Standard Potassium Iodate
ii) Dissolve 0.566 g KI03, dried at 1200C, and 0.5 g NaHC03 in distilled water, and dilute
to 1000 ml. The equivalence of this titrant is 1.0 mg Na2SO
3per 1.00 ml.
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iii) Potassium Iodide Solution, (50 g per litre)-Dissolve 50 g of iodate-free KI and 0.5g of
sodium bi-carbonate (NaHC03) in freshly boiled and cooled water and dilute to one litre.
iv) Starch indicator.
v) Hydrochloric Acid, 1 +1
6.3 APPARATUS REQUIRED
250 c.c erlemneyer flask
10 c.c pipette ( for 1:1 HCl )
100 ml pipette (for the sample to be measured)
5 ml pipette ( for the sample to be measured )
1 ml burette ( for KIO3
titrant)
6.4 PROCEDURE
Place 10 ml 1 + 1 HCl in a 250 ml flask. Rapidly add 100 ml. sample, submerging the pipette
tip below the acid surface to minimize air exposure. After adding I ml. starch indicator solution
and 5 ml KI solution, titrate ivith standard KI03 titrant to the first appearance of a persitent blue
colour. Determine the blank titration by carrying 100 ml. distilled water through the complete
procedure.
SO3
milligrams per litre = (A-B) x 6.35
Na2SO
3milligrams per litre = (A-B) x 10
Where A = millilitres of titration for sample.
B = millilitres of titration for blank.
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FIG.2 WINKLER FLASK FOR DISSOLVED OXYGEN
DETERMINATION
FIG.1 METHOD OF COLLECTING SAMPLE FOR OXYGEN
DETERMINATION ON HOT FEED WATER
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7. DETERMINATION OF DISSOLVED OXYGEN (MORE THAN
0.10 PPM)
7.1 SAMPLING
It is important to use air-tight connections in all apparatus used for sampling and testing. When
sampling hot water, a water cooled coil should be introduced into the sampling line. A convenient
arrangement for sampling for feed water is shown in the figure. The sample itself should be taken
in a 500 ml. Winkler flask, containing a few glass beads, as shown in figure and water should
flow through for atleast 10 minutes before taking the actual sample so as to displace all traces
of air. Care must be taken to see that air bubbles do not form around the stopper of the Winkler
flask while sampling.
7.2 REAGENTS REQUIRED
i) Manganous chloride
Dissolve 400gms of Manganous chloride(AR) in one litre of DM water.
ii) Alkaline iodide
Dissolve 600 gm of potassiumhydroxide and 140gm of potassium iodide in 1litre of water.
iii) N / 100 Sodium thiosulphate
Dissolve 2.482gm of AR Sodium thiosulphate(Na2S2O25H2O) in water and make up to
one litre. Add about I gm of AR Sodium carbonate to preserve the solution. Standardise
against standard potassium dichromate.
iv) Sulphuric Acid 1:1
Add 250ml of conc.sulphuric acid to 250 ml of water. Cool and store.
7.3 GLASSWARES
Winklers flask arrangement as shown in the figure.
2ml pipette
Burette 50 ml - 1 No.
7.4 PROCEDURE
By means of the funnel fitted to the Winklers flask, add 2 ml of the manganous chloride solution
and then add 2 ml of the alkaline Iodide soldtion. Mix, allow to stand for 10 minutes and then add
2 ml of 1:1 H2 SO4. Take 250 ml of the sample and titrate the liberated iodine with N/100
Thiosulphate solution using starch as indicator.
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ML of Oxygen / Litre = ML of N/100 Thio used x 0.224
1 ML of Oxygen / Litre = 1.430 Mg / Litre
8. DETERMINATION OF PERMANGANATE NUMBER (Determining
organic substances : Potassium Permanganate Consumption)
8.1 OXYGEN CONSUMED FROM PERMANGANATE
Two versions of the oxygen consumed from permanganate method are in the use for estimating
the strength of organic pollution in streams. One modification hastens the oxidative reaction by
elevating the sample temperature over a shorter time. The other determination is conducted near
room temperature for an extended period. Since both procedures are empirical, experimental
conditions must be uniform for the results to have significance. Clean glassware is mandatory.
8.2 REAGENTS
i) Standard potassium permanganate solution, 0.0125 N-Filter the supernatant from an
aged solution of 0. 1 N KMnO4 through sintered glass crucible, and dilute 12.5 ml to
100 ml withdistilled water. Standardize the solution daily. The equivalence of 0.0125 N
KMnO4 is 0.100 mg oxygen consumed per 1.00 ml.
Sulphuric acid solution,1 + 3 - Add 0.0125 N KMnO4 solution until a very faint colour
persists after 4 hours.
Sodium sulphide dechlorinating solution, 0.025 N 1.575 g per 100 ml.
ii) Reagents for Half-hour method
Standard Ammonium oxalate titrant, 0.0125 N Dissolve 0.8882 g. (NH4)2 C2O4. H2O,
dried at 105o C and dilute to 1000 ml with distilled water.
iii) Reagents for pour hour method
Standard sodium thiosulphate titrant, 0.0125 N. In a 1 litre volumetric flask place 0.6 g
NaHCO3 and dilute 12.5 ml 0.1 N Na2S2O3 with distilled water, Prepare daily and
standardize.
Starch Indicator.
Potassium Iodide.
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8.3 PROCEDURE
When the residual chlorine exceeds 0.5 mg per litre, dechlorinate the sample with a minute
amount of 0.025 N Na2SO3 solution to the 0.65 mg per litre level. Do not dechlorinate
completely.
i) Half hour method
Pipette 100 ml well-mixed sample and 100 ml distilled water into separate 250 ml flasks,
and treat both the sample and blank alike throughout the procedure. Add 10 ml (1+3)
H2SO
4and 10.00 ml standard 9.0125 N KMnO
4. Immerse the flask in a boiling water
bath for exactly 30 min. making certain that the liquid level in the flask is completely
submerged in the boiling water throughout- the entire period. If the KMnO4colour in the
sample grows faint or disappears, take a smaller volume and dilute to 100 ml standard
0.0125 N (NH4)
2C
2O
4solution, and while still hot, titrate with standard 0.0125 N
KMnO4
to a faint pink end-point.
Oxygen consumed from KMnO4
milligrams per litre = (A-B) x N x 8000 / millilitres of
sample
Where A = Millilitres of titration for sample
B = Millilitres of titration for distilled water blank, and
N = Normality of KMnO4
titrant.
(ii) Pour- hour method
Measure 250 ml well mixed sample and 250 ml distilled water into separate 400 ml glassstoppered bottles, and bring to 27C. Treat both the sample and blank alike throughout
the procedure. Add 10 ml (1+3) H2SO4 with a volumetric pipette introduce an appropriate
volume of standard 0.0125 N KMn04- Select a KMnO4
volume in sufficient excess to
require a back-titration of 5 to 15 ml at the end of 4 hour and in any case, use no less than
10.0 ml KMnO4. Gently rotate the bottle to mix the contents, and place in a water bath or
incubator at 27C for exactly 4 hours. Several times during the incubation, mix, by gentle
rotation, any sample that contains appreciable suspended matter. Cool to room temperature
and a few small crystals KI,mix, and titrate the contents of the bottles with standard 0.0125N
Na2S2O3 titrant.
Add 1.0 ml starch indicator when the colour turns pale straw, and complete the titration tothe first disappearance of the blue colour.
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9. DETERMINATION OF EVAPORATION (T.D.S.) IGNITION
RESIDUES AND VOLATILE MATTER
9.1 EVAPORATION RESIDUES AT 105C
i) Apparatus required
200 c.c Capacity platinum evaporation dish
100 c.c & 200 c.c Pipettes to measure water to be tested
Water bath
Drying oven
Desiccator
Ignition furnace
ii) Procedure
100 c.c or possible a greater quantity of water to be tested (filter if suspended solids are
present - estimate separately suspended solids content) is evaporated in a platinum dishon a water bath until it is dry, after which it is dried down, to constant weight in a drying
oven at 105C. It is weighed after cooling in the desiccator.
9.2 DETERMINING THE IGNITION RESIDUES
The evaporation residue determined at 105C as described above is ignited in an ignition furnace
at 600 + 25C until constant weight. Cool in the desiccator and weigh. Constant weight shall be
considered as attained when the change in weight of the dish plus residue shall not be > 0.5 mg
between two successive operations involving heating, cooling in a desiccator and weighing.
9.3 DETERMINING THE VOLATILE MATTER
Record the loss in weight in the previous determination as weight of volatile dissolved matter.
9.4 CALCULATIONS
Total dissolved solids ppm A/W x 1000
Ignition residue ppm B/W x 1000
Volatile matter ppm (A-B) / W x 1000
Where A = gms of dissolved matter
B = gms of ignition residue
(A-B) = gms of volatile matter
W = ml / weight of sample used
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10. DETERMINATION OF OIL (Fluorocarbon matters)
10.1 INTRODUCTION
In the determination of oil, an absolute quantity of a specific substance is not measured.
Rather,group of substances with similar, physical characteristics are determine quantitatively
on the basis of common solubility, in specified solvent. The constituent analysed may
therefore be said to include hydrocarbons, fatty acids, soaps, fats, waxes, oil and any
other material that is extracted by the solvent form an acidified sample.
10.2 REAGENTS
Acetone
Hydrochloric acid
Sodium bisulphate. (NaHSO4
H20)
Sodium chloride
Sodium sulphate (Na2SO
4)
Sulphuric acid
Fluorocarbon solvent (1,1,2-Trichloro-1,2,2-Trifluoro ethane)
10.3 APPARATUS
Drying oven
Evaporating flask
Separatory funnel
Steam bath
Desiccator
10.4 PROCEDURE
Dry a boiling flask in an oven at 105oC for lhr and cool in a desiccator. Weigh accurately,
(W1g).
Collect the sample in a glass container. Note the volume. Add HCl (1:9) dropwise and
adjust the pH to 3.0 & 4.0 pour the acidified sample into a separatory funnel.Add 60 ml.
of fluorocarbon solvent to the glass container in which the sample is collected. Cap and
shake the bottle well. Pour the solvent into the separatory funnel. Extract the sample by
shaking vigorously for 2 minutes. Invert the separatory funnel and vent with stopcock to
relieve pressure built up during the extraction. Allow the layers to separate. Drain the
solvent layer through filter paper (whatman) held by a small funnel- into the tared boilingflask. (if emulsion problems are anticipated, add 1 to 2g of sodium sulphate to the filter
paper cone and slowly drain t he solvent through the crystals, If a clear solvent is not
obtained, add about 100g of sodium chloride to the separatory funnel. Frequently this will
break the emulsion).
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Repeat the bottle rinse and extraction with two additional 60ml portion of the solvent.
combine all the solvents in the same boiling flask.Rinse the filter with 20ml of the solvent
into the same flask.Evaporate (in a fume hood) the solvent from the boiling flasks in a
steam bath. When the contents have been evaporated to dryness, (without any solvent
vapour or residual water), carefully wipe the exterior of the flask with a lint free cloth and
a small amount of acetone to remove any water adhering to the flask. Place in a desiccator
for 1 hr and weigh (W2
g)
10.5 CALCULATION
Extractable residue (mg/litre) = (W2-WI) x 1000 / ml.sample
11. DETERMINATION OF pH-VALUE
11.1 INTRODUCTION
As a yard stick for the concentration of hydrogen ions, the pH value gives an indication of
the percentage reaction (alkalinity or acidity) of the water and hence its aggressive nature.
The pH value is the negative logarithm to the base 10 of the hydrogen ion concentration,
expressed as gram-ions per litre.
The pH value of a given solution depends on the temperature and as a rule it is quoted for
250 C. Water with pH = 7 has a neutral reaction, while there is an acidic reaction at pH7.
11.2 APPARATUS REQUIRED
pH meter with Associated glass and reference electrodes.
Buffer tablets of known pH.
11.3 ELECTROMETRIC DETERMINATION OF PH VALUE
With the electrometric method, the pH value is determined from the potential difference
between the measuring electrodes immersed in the liquid under test and a reference electrode
of known potential. For testing water, electrode assemblies comprising a glass electrode
and a calomel reference electrode are suited.
pH meter is to be operated in accordance with the instruction supplied with it, by its
manufacturer.
Where water is very pure, and the pH value and electrical conductivity are being determined
simultaneously, make sure that the pH electrodes are inserted. After the conductivity
electrodes if the measuring points are connected in series.
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11.4 ELECTRODE TREATMENT
New glass electrodes and those that has been stored dry shall be conditioned and maintained
as recommended by the manufacturer. If the assembly is in intermittent use, keep the
immersed ends of the electrodes, in water between measurements. For prolonged storage,
glass electrodes may be allowed to become dry, but the junction and filling openings of
reference electrodes should be capped to reduce evaporation.
11.5 STANDARDISATION OF ASSEMBLY
Turn on the instruments, allow it to warm up and bring it to electrical balance in accordance
with the manufacturers instructions. Wash the glass and reference electrodes and the
sample cap by means of a flowing stream of distilled water from a wash bottle. Note the
temperature of the test solution and adjust the temperature dial of the meter to correspond.
Select the two reference buffer solutions, near the pH of the test solution. (Buffer solutions
can be prepared from the buffer tablets following manufacturers instructions). Warm or
cool these reference solutions as necessary to match within 20 C the temperature of the
unknown.
Fill the sample cup with the first reference buffer solution, and immerse the electrodes.Engage
the operating button, turn the range switch if present to the proper position, and rotate the
assymmetry potential knob until the reading of the dial corresponds to the known pH of
the reference buffer solution. Repeat the above procedure until two successive instrument
readings are obtained, without changing the setting of the asymmetry potential knob. Care
should be taken to see that the level of the KCIsolution in the referencce electrode must
always be kept more than that of the measured solution. To reduce the effects of thermal
and electrical hysteresis, the temperature of electrodes reference buffer solutions and wash
water should be kept as close to that of the unknown sample as possible.
Wash the electrodes and sample cup three times with water. Place the second reference
buffer solutions in the sample cup, and measure pH. Do not change the setting of assymmetry
potential knob.
The assembly shall be judged to be operated satisfactorily if the pH reading obtained for
the second reference buffer solution agrees with its assigned pH value within 0.05 unit.In
long series of measurements, supplement initial and final standardisations by interim checks.
Wash the electrodes by means of a flowing stream from a wash bottle. Place the water
sample in a clean glass beaker. Measure the temperature. Insert the electrode and measure
pH as before.
11.6 INSTRUCTIONS
pH meter should be checked Periodically for its performance using buffer.
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12. DETERMINATION OF CONDUCTIVITY (Conducto Bridge Method)
12.1 CONDUCTANCE (SPECIFIC)
The specific conductance of water is a measure of the ability of the water to conduct an
electrical current. This property is of no consequence in itself with respect to water treatment.
However, from a control stand point, the conductivity test is important as a direct measure
of the total ionizable solids in the water. The conductivity test provides quick measurement
of steam purity as well as a simple control for boiler water solids. Conductivity also may
be used for blowdown control in recirculating cooling water systems.
Specific conductance is inversely proportional to electrical resistance. Pure water is highly
resistant to the passage of an electric current and therefore has a low specific conductance.
However, if the water contains ions, the water becomes a better conductor of electricity
and the specific conductance is increased. Inorganic compounds such as sodium chloride
and sodium sulphate dissociate into positive and negative ions, which will conduct electricity
in proportion to the amount of ions present. The conductivity test, therefore, is not specific
for any one ion, but rather a measure of the total ionic concentration.
The basic unit of electrical resistance is the ohm. since electrical conductivity is the reciprocal
of resistance, the unique term mho (ohm spelled backwards) was chosen as the basic
unit of conductivity. In the conductivity test, small amounts of electrical conductance are
measured and the instrument is usually calibrated in micromhos (a micromho is a millionth
of a mho). To calibrate a conductivity instrument to read directly in parts per million of
dissolved solids (or some specific ion or compound) is not recommended since such a
calibration introduces an error into the instrument reading itself. The conversion factor
from micromhos of specific conductance to parts per million will vary slightly with different
waters. To include a constant conversion factor in the instrument calibration is to introduce
an unnecessary source of error.
The conductivity test provides an accurate and simple method of blowdown control.
However, certain limitations must be considered. While the conductivity test measures the
total ionic concentration, the hydroxide ion has a much higher conductance than the other
ions present.Thus for accurate results the sample must be neutralised before the conductivity
test is made.
Conductivity is an exceedingly sensitive test and is accurate down to the level of
approximately 0.5 - 1.0 ppm ionizable solids. Until development of the flame
Spectrophotometer method for determining low sodium concentrations, conductivity was
the most accurate method of determining steam purity.
12.2 APPARATUS REQUIRED
1-Conducto Bridge (0-5 to 0-5000 micro mho/cm with selector switch)
1-Dip cell
1-Cylinder, rimmed glass, not graduated
1-Thermometer, dial type (0- 100C)
1-Measuring cup , brass
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12.3 CONDUCTANCE OF BOILER WATER
Theory of test: The ionizable solids in boiler water have the ability to conduct an electric
current through a solution. This property of electrical conductance of solids makes it possible
to accurately measure the quantity of solids in solution by suitable conductance equipment.
12.4 CHEMICAL REQUIRED.
Gallic Acid
12.5 PROCEDURE FOR TEST
Pour approximately 50 ml of distilled water or steam condensate into the rimmed glass
cylinder and insert the conductivity cell. Move cell up and down several times to wash off
any solids present on the cell. Discard the water in the cylinder.
Pour approximately 50 in of boiler water into the cylinder (use a settled or filtered sample),
Add two dippers of gallic acid (approx. 0.2 g) to the sample. (Note: if a small amount of
the gallic acid remains undissolved, the conductivity test will not be adversely affected).
Measure temp of the sample and adjust the temperature correction dial on the conducto
Bridge to the proper temperature. Insert conductivity cell and move up and down several
times to insure equilibrium. Measure the specific conductance on the Conducto Bridge by
turning the conductivity dial until the electric or magic eyes is at its widest black angle.
Note: Two dippers of gallic acid will neutralize approximately 130 ppm of P alkalinity.
On some highly alkaline boiler waters, additional gallic acid may be required. A desirable
precaution is to add approximately four drops phenolphothalein indicator to the sample
and delay taking the conductivity reading until the pink colour has been completely
discharged by the addition of gallic acid.
12.6 CALCULATION OF RESULTS
The specific conductance in micromhos is read directly from the calibrated scale as indicated
by the pointer on the conductivity knob, when the eye is at its widest black angle.
The relationship between specific conductance and the dissolved solids content of a boiler
water depends on the characteristics of each individual boiler water and therefore may be
slightly different for each plant. Using the gallic acid neutralization method, an average
value determined over a wide range of operating conditions is that one micromho is equivalent
to 0.9 pprn dissolved solids. This value is sufficiently accurate for the average industrialplant.
The exact relationship between micromhos and solids can be individually established for
each plant by determining both the conductance and solids content of a series of
approximately ten sample taken over a two week period.
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12.7 LIMITATIONS OF TEST
The conductance method affords a rapid means of checking the dissolved solids content
of a sample. The effect of hydroxide in causing high conductivity is minimized by the gallic
acid neutralisation, thereby securing a consistent relationship between solids and
conductance. The conductance method does not measure non-electrolytic solids such as
organic matter, and in order to express results in terms of parts per million of boiler water
solids it is necessary to use a conversion factor.
12.8 CONDUCTANCE OF STEAM CONDENSATE AND FEEDWATER
i) Theory of test
The ionizable solids and gases in condensed steam and feed water have the ability to
conduct an electric current through a solution. In evaluating the conductance of condensed
steam and feed water samples, it is necessary to check for the presence of dissolved gases
such as ammonia and carbon dioxide which impart conductance. The effect of ammonia is
predominant and hence the sample is allowed to pass through a cation resin column (in H
+
form). An arrangement of resin column is shown figure 1. Ammonia is removed by this
method and. the conductivity measured will indicate the dissolved solids present.
The solids are converted to their corresponding acids by passing the sample through the
cation column and the approximate conductance of acids to ppb relationship can be as
follows:
Weak acids (H2CO
3,HAC =0.004 mmho/ppb (as CaCO
3)
Strong acids (HCl, H2SO
4, HNO
3) =0.007 mmho/ppb (as CaCO
3)
Cation conductivity measuring less than 0.3 micromho/cm will mean total solids in the
sample less than 50 ppb.
ii) Procedure for the test
Collect approximately 50 ml of the condensed sample after passing through the cation
column (in the H+
form). The effluent sample is measured for its conductivity.
For measuring conductivity above 10 micromho/cm, either a flow type or dip type cell
may be used. For samples with conductivity below 10 micromho/cm flow type conductivity
cell tube used. Adjust the sample stream to proper flow rate and temperature.(250 C).
Read the conductance by continuous (on-line) measurement.
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iii) Regeneration procedure for cation column
The cation resin in the H+ form when exhausted should be regenerated as per the procedure
described below:
iv) Backwards flushing
To remove contaminations, first shake the cation exchange thoroughly by hand then allow
condensate to flow through from the bottom upwards for about 5 minutes until the discharge
rinsing water is clear and colourless. Watch that no resin is flushed out.
v) Regenerating
For regenerating the exchanger resin allow 6 litres of technical hydrochloric acid 1:4 diluted
with condensate per I litre of resin to flow through the apparatus from the top downwards
for at least 30 minutes. (Flow rate approximately 8- 10 litres/hr.) There must be no air
bubbles on the bottom of the sieve, since these inhibit the flow and affect the regeneration.
The discharge is strongly acidic and must only be emptied into an acidresistant drain.
vi) Flushing-out
For 30 to 40 minutes in any case until the Cl-reaction (check with AgNO3) has disappeared
flush-out the remaining acid in the apparatus with condensate from the top downwards.
Flow rate 20- 30 litres/hr.
vii) Start-up
Before starting up again check once more to see whether there is any air bubbles on the
bottom of the sieve: otherwise, the cation exchanger will operate irregularly and inefficiently.
viii) Remarks
If the exchanger resin is considerably contaminated with iron oxides or other deposits, the
regenerating acid may be heated to 500 C and left for about half an hour in the resin before
flushing. ( Temperature resistance of the resin: Max.1000 C ). Following this backwards
flushing will have to be carried out again, if necessary, to remove any released particles
from the resin.
Resin contaminated with oil can be cleaned with. a detergent.
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FIG.3 HYDROGEN ION EXCHANGER OF PLASTIC FOR
MEASURING CONDUCTIVITY
13. DETERMINATION OF DISSOLVED OXYGEN
Colorimetric determination of low concentration of dissolved oxygen in water less than 0.10 ppm.
13.1 INTRODUCTION
This method uses the dissolved oxygen in the sample to oxidise a reduced solution of
indigo carmine. As the reduced solution of indigo carmine is oxidised, it changes colour
progressively from yellow to orange to pink to red to purple to green.
13.2 REAGENTS
i) Reagent solution
About 30 minutes before testing, add 20 ml of indigo carmine solution and 5 ml of
potassium hydroxide solution to a small beaker. Stir gently and pour into a 50 mlburette.
ii) Indigo carmine solution
Dissolve 0.018 gm of indigo carmine and 0.2 gm of dextrose in 5 ml. of boiled
eionized water. Add 75 ml of glycerol and stir well. This reagent should be used
within two weeks.
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iii) Potassium hydroxide solution
Dissolve 100 gms of potassium hydroxide in 200 ml of boiled deionized water.
13.3 GLASSWARES
BOD bottle 300 ml capacity with grounded neck
and stopper - I No.
Burette (50 ml capacity) - 1 No.
White porcelain tile - 1 No.
The colours produced by mixing the coloured solutions given below can be used as reference
for determining the dissolved oxygen content by indigo carmine test.
i) Colour standards
Stock solutions
a. Red colour standard (CS-A)
Dissolve 59.29 g of cobaltous chloride hexahydrate (COCl2.6H2O) in
sufficient HCl (1 : 99) to make one litre.
b. Yellow colour standard (CS-B)
Dissolve 45.05 g of Ferric chloride hexahydrate (FeCl3 6H2O) insufficient HCl (1:99) to make one litre.
c. Blue colour standard (CS-C)
Dissolve 62.45 g of cupric sulphate pentahydrate (CUSO4 5H2O) in
sufficient HCl (1:99) to make one litre.
ii) Store all stock solutions in dark-coloured bottles to prevent fading.
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iii) Preparation of colour standards
Prepare a series of colour standards as listed in the following table:
Disolved Oxygen Milliliters of colour standard
ppm CS-A CS-B CS-C
0.000 0.75 35.0 ---
0.005 5.00 20.0 ---
0.010 6.25 12.5 ---
0.015 9.40 10.0 ---
0.025 14.4 3.8 ---
0.050 18.3 1.7 ---
Place the amounts of stock solutions in the table in 300 ml borosilicate glass stoppered reagent
bottles. Add 2.3 ml of HCl (sp.gr.1.19) to each and dilute to the neck of the bottle with water.
Stopper the bottle and mix by inversion. Store in a dark place to minimise fading of colours.
13.4 PROCEDURE
i) Attach a minimum length of rubber tubing tipped with about a 4" piece of glass
tubing to the sample point.
ii) Insert the glass tubing to the bottom of the BOD bottle of 300 ml.capacity, having
a raised lip around the neck and glass stoppers ground to a conical lower tip. Permit
the sample to fill and overflow the bottle an equivalent of at least 10 times. The
sample should be at room temperature or below.
iii) Remove the glass tipped rubber tubing slowly.
iv) Insert tip of the burette containing the reagent, below the neck of the bottle and add
4 ml of the reagent.
V) Remove the burette, carefully stopper the bottle and shake well.
vi) Determine the colour immediately by placing the bottle in a white surface and view,
looking into the bottle at 450 angle.
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ppm Color
0.000 Yellow
0.005 Orange
0.010 Orange pink
0.015 Pink
0.025 Pink red
0.050 Red purple
14. DETERMINATION OF SOLUBLE SILICA
14.1 SUMMARY OF METHOD
This colorimetric method depends on forming molybdi-silicic acid by reacting the silica
and ammonium molybdate in acid solution. I-amino-2 napthol-4 sulfonic acid is then added
to reduce the molybdi-silicic complex. The method is designed to determine soluble silica
with high accuracy in the range of 5 to 1000 g/ litre [1g/litre =1 ppb.]
14.2 REAGENTS
i) Amino - naptho l- sulfonic acid solution - Dissolve 0.5 g of 1-amino-2napthol
4- sulfonic acid in 50 ml of a solution containing 1 g sodium sulphite (Na3 SO3).After is solving, add the solution to 100 ml of a solution containing 30 g of sodium
hydrogen sulphite (NaHSO3). Make up to 200 ml and store in a dark, plastic
bottle. Prepare a fresh solution every 2 weeks.
ii) Ammonium molybdat e solution - (100 g/litre) Dissolve 10 grams of ammonium
molybdate tetrahydrate in 100 ml of deionized water. Filter this solution each day
before using.
iii) Hydrochloric Acid (1 + 1) - Dilute 1 volume of concentrated hydrochloric acid
(HCl, sp. gr. 1.19) with I volume of deionized water.
iv) Oxalic Acid Solution - (100 g/litre) - Dissolve10 grams of oxalic acid dihydrate
(H2C
2O
42H
2O) in 100ml. of deionized water.
v) Silica, Standard solution (1 ml =1mg. Si02) - Dissolve 4.732 g of sodium
metasilicate (Na2SiO
39H
2O) in water and dilute to 1 litre. Check the concentration
of this solution in accordance with Reference Method A. (ASTM 859). Silica
standards may be purchased from several chemical supply houses.
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14.3 APPARATUS REQUIRED
i) 50 ml - pipette
ii) 250 ml - polyethylene container
iii) 1 ml pipette (for 1: 1 HCl)
iv) 2ml pipette (for ammonium molybdate solution)
v) 2ml pipette (for oxalic acid solution)
vi) 2ml pipette (for ANS solution)
vii) Spectrophotometer
14.4 PROCEDURE
i) Pipette 50 ml of clear sample into a 250 ml polyethylene container
ii) Add I ml of 1 + 1 HCI solution
iii) Add 2 ml of ammonium molybdate solution
iv) Wait 5 minutes. The sample should be swirled during this period.
v) Add 2.0 ml of oxalic acid solution. Swirl to mix wait for 2 min.
vi) Add 2.0 ml of I-amino-2-napthol-4 sulfonic acid solution and swirl.
vii) Wait 5 minutes. Read on spectrophotometer at 815 nm. Transmittance of the reagentblank versus deionized water should not be less than 98.8%
14.5 CALIBRATION
Prepare a series of atleast 4 standards by proper dilution of the standard silica solution.Treat
50 ml aliquots of the standards in accordance with steps given under the procedure. (14.4)
Prepare a blank using a 50.0 ml aliquot of DM water that has been similarly treated. Read
the absorbance values from the spectrophotometer at 815 nm (A separate calibration
curve in the wave length range of 640 to 700 nm can also be prepared but with less
sensitivity)
14.6 CALCULATION
Silica concentration of the unknown solution can be read directly form the calibration
curve.
15. DETERMINATION OF TOTAL SILICA
15.1 INTRODUCTION
Some boiler stations using ion exchange columns for preboiler water purification, have
noticed silica concentrations building up in the units and at the same time a soluble silica
analysis onwater coming from the ion exchange column showed no silica. Analysis for
colloidal silica on these same samples showed the -silica was present as colloidal particle.
This technique has been developed as an analytical procedure to accurately determine
trace concentrations of silica where all or a part is present in colloidal form. Total silica is
determined spectrophotometrically after solubilization by the pressurized bomb method.
(Paar Oxygen Bomb).
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15.2 APPARATUS REQUIRED
-25 ml , 50 ml, 10 ml - pipette for suitable aliquot sample
-Platinum cup with cover
-Oxygen bom
-1 ml pipette
-10 ml -Pipette (for deionized water)
-Nitrogen cylinder with pressure regulator, opener etc.-AIROVEN to be capable of giving a temperature 1900C. for 12 hours continuously
- Spectrophotometer.
15.3 PROCEDURE
i) Accurately measure 50 ml or a suitable aliquot of the sample into a platinum cup.
ii) Add I ml of 0.2 N NaOH and close the cup with a platinum cover
iii) Place the closed cup in a Paar oxygen bomb containing 10 ml of deionized water
and completely assemble the bomb.
iv) Nitrogen is added to obtain 30 pounds pressure and let out five times to completely
flush out oxygen in the bomb to prevent bomb corrosion.
v) Pressurize the bomb with nitrogen to 45 psig (maintained for specified period) and
place in an oven at 190o C for 8 hours. The oven should be placed in a hood since
all gaskets in the bomb are made of Teflon.
vi) Remove the bomb from the oven, cool, and remove the sample from the platinum
cup silica is determined spectrophotmetrically
15. 4 CALCULATION
i) See silica curve for the spectrophotometer used.
ii) Colloidal silica (ppm) = Total silica (ppm) -Soluble silica (ppm).
16. DETERMINATION OF ORTHOPHOSPHATE
16.1 INTRODUCTION
This method is applicable to the routine determination of orthophosphate in the 2 to 25
ppm PO4 range in industrial water and is based on the photometric measurement of the
yellow colour of the molybdo vanadophosphoric acid produced. The colour intensity is
proportional to the orthophosphate concentration in the sample. Highly coloured water
such as tannin treated boiler water and high concentration of ferric iron interfere thus
requiring preliminary treatment to remove these materials.
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16.2 REAGENTS
i) Ammonium vanadomolybdate solution - Dissolve 40 grams of ammoniummolybdate
tetrahydrate (NH4) MO
7O
24, 4H
20) in 400 ml of water. Dissolve1.0 gram of
ammonium metavanadate in 300 ml of water and add 200 ml concentrated nitric
acid (Sp. Gr. 1.42). Add the first solution to the second solution, mix well, and
dilute to one litre with water.
ii) Phosphate standard solution (1 ml= 1 mg PO4) -Dissolve 1.433 grams of oven-dried
(4 hours at 1050 c). Potassium dihydrogen phosphate (KH3PO
4) in water and
dilute volumetrically to one litre.
16.3 APPARATUS REQUIRED
i) 125 ml Erlenmeyer flask
ii) 50 ml , 25 ml , 10 ml pipette for suitable aliquot sample
iii) Filter stand with funnel, whatman No.42 filter paper etc.
iv) 25 ml graduate (for Ammonium vanadomolybdate solution)
v) Spectrophotometer
16.4 PROCEDURE
i) To a 125 ml Erlemneyer flask, add 50 ml of the clear sample or aliquot there of
diluted to 50 ml with deionized water.
ii) Add, using a graduate, 25 ml of ammonium vanadomolybdate solution and mix well
by swirling.
iii) Allow 10 minutes for colour development and read within 30 minutes on the
spectrophotometer at 400 nm.
iv) Reagent blank and atleast two phosphate standards should be run along with samples.
16.5 CALIBRATION AND STANDARDIZATION
Prepare a series of standards to cover the range of 25 mg / litre (ppm) and preparecalibration curve.
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17. DETERMINATION OF IRON - BATHO PENANTHROLINE METHOD
17.1 INTRODUCTION
This method covers the determination of total iron in the range of 0-200 ppb. This method
is based upon the red ferrous complex produced by the bathophenanthroline and reduced
iron. The addition of hydroxylamine hydrochloride reduces ferric to ferrous with the pH
adjusted between 3.3 and 3.7 before extracting the complex with n-hexylalcohol.
17.2 SAMPLING
Although samples may be taken in polyethylene bottles, it is recommended that meticulously
clean 500 ml glass bottles with plastic caps be used. Prepare bottles by soaking in hot HCl
(l +1) for several hours prior to use. Drain and flush several times with iron-free water.
Add 1 ml of concentrated HCl to each 500 ml bottle and cap until used. When taking
sample, be sure, sample point has been continuously running for atleast four hours. Do not
overflow the acidified sample bottle during sample collection.
17.3 STANDARDS
Prepare a series of iron standards in 250 ml. separatory funnels to cover the range expected.
Use the iron std. solution (I ml=0.001 mg Fe). include a zero blank and follow procedure.
17.4 REAGENTS
i) Alcohol - lsopropyl
ii) Alcohol - n-hexyl
iii) Ammonium hydroxide (1 + 1)
iv) Hydrochloric acid concentrated and HCI (1+9)
V) Bathophenanthroline solution (0.835 g/litre). Dissolve 0.0835 of 4,7 dipheny
1-1, 10-phenanthroline in 100 ml of ethyl alcohol (95%)
vi) Hydroxylamine hydrochloride solution (100 g/litre). Dissolve 10 g of NH2OH HCl
in water and dilute to 100ml. Purify as follows: Adjust pH to 3.5 using a pH meter
by dropwise additions of NH2OH(1+1) and HCl (1+9). Transfer to a separatory
funnel. Add 6ml.of bathophenanthroline solution and shake. Let Stand for 1 minute.
Add 20 ml of n-hexyl alcohol and shake for I minute. Let separate, remove aqueous
layer and discard alcoholic layer. Repeat extraction by again adding 3 ml of
bathophenanthroline solution and 20 ml of alcohol with mixing. If no further extractions
are indicated, make an extraction with alcohol alone and let settle a long enough
time to remove all of the alcohol layer. Discard the alcohol layer.
vii) Iron, standard solution (1 ml =0.1 mg Fe). Dissolve 0. 1000 g of pure iron in 10 ml
of HCl (1+1) and 12 ml of bromine water. Boil until excess bromine is removed.
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Add 200 ml of HCI (1+1) cool and dilute to I litre in a volumetric flask with water.
Iron, standard solution (1 ml=0.001 mg Fe) Pipette 10 ml of standard solution
(1ml=0.1mg Fe) into a I litre flask, add 12 ml of HCl (1+1) and dilute to1 litre with
iron-free water. Prepare the dilute solution fresh before use.
viii) Thioglycollic acid - reagent grade.
17.5 GLASS WARE
All glasswares must be cleaned in HCl before making an iron extraction. Drain and
rinse with isoprophyl alcohol.
17.6 APPARATUS REQUIRED
- 500 ml polyethylene bottles with sample extraction hose.
- 250 ml separatory funnel
- 2 ml pipette (for conc. HCl)
- 2 ml pipette(for NH2OH HCl)
- 2 ml pipette (for bathophenanthroline)
- 2 ml pipette (for thiogly collic acid)
- 25 ml pipette (for n-hexyl alcohol)
- 10 ml pipette (for iso-propyl alcohol)
- Spectrophotometer
- 5.0 cm cell - 0-5 ppb
- 2.0 cm cell - 50-200 ppb
- waterbath suitable for heating (thermostat)
17.7 APPLICATION RANGE OF APPARATUS
Set spectrophotometer at 533 nm
5.0 cm cell 0-50 ppb
2.0 cm cell 50-200 ppb
17.8 PROCEDURE
i) Place acidified sample bottle (with top off) in hot water bath for one hour after
adding 2 ml of conc. HCl, 2ml of NH2OH HCI, and 2 ml of thioglycollic acid (see
Note).
ii) Cool to room temperature and transfer 200 ml of the samples to a 250 ml separatory
funnel.
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NOTE:
The pH of a 500 ml feed water sample which has been acidified with 1 ml of
concentrated HCl is approximately 1.5. At this low pH nearly all the iron oxide
(Fe2O
3+Fe
3O
4) in the feed water will generally go into solution over a short period of time.
However, the above digestion step in the water bath gives some assurance of complete
solubility. Nevertheless an occasional sample will require prolonged heating and
concentration. A magnet drawn across the bottom of the sample bottle that has beenstanding several hours will usually attract insoluble magnetite
iii) Add 1ml of NH2OH HCl and then 2 ml. of bathophenanthroline. (Shake for 30seconds).
(Add 3 ml. for over 50 ppb Fe).
iv) Adjust pH with NH2OH (1+1) or HCl (1+9) to pH 3.3 to 3.7. (This can be done with a
single pH elecctrode hung down in the separatory funnel). Rinse electrode with distilled
water before going to next sample.
V) Add 25 ml. of n-hexyl alcohol and shake for 1 minute. Allow 5 minutes for separation and
drain aqueous phase.
vi) Add 10ml. of isoprophyl alcohol to the funel and swirl to clear solution.
vii) Read colour.in the appropriate cell.
NOTE:
Isoamyl alcohol can also be used in place of Isopropyl alcohol.
18. DETERMINATION OF COPPER-NEOCUPROINE METHOD
18.1 INTRODUCTION
This method covers the determination of total copper in the 2 to 2000 ppb range. This
method is based upon the yellow colour produced by the neocuproine cuprous complex.
A buffer solution maintains the pH between 4.0 to 6.0, but full colour development takes
place over the range of 2.3 to 9.0. The hydroxylarnine hydrochloride reduces the copper
to the cuprous state.
18.2 SAMPLING
Although samples may be taken in polyethylene bottles, meticulously clean 500 ml glass
bottles with plastic caps are preferred. Prepare bottles by soaking in HNO3 (1+9) for
several hours prior to use. Then rinse bottles with distilled water and drain before sampling.
Take the sample from the sample point, which has been continuously running for at least
four hours. Do not overflow or rinse bottle. Do not touch valve or jar line.
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18.3 STANDARDS
Prepare a series of copper standards in 250 ml separatory funnels using the standard
copper solution (1 ml =4 mg Cu). Add 1.0 ml of 1+1 HCL Dilute each to 200 ml include
a blank and gtreat similarly.
Application Range of Apparatus
Set spectrophotometer at 454 nm1.0 cm cell 20 to 1000 ppb.
10.0 cm cell 2 to 100 ppb.
18.4 REAGENTS
i) Copper, Standard Solution (1 ml =0.02 mg Cu) weigh 0.200 g of electrolytic
copper. Place it in a 250 ml beaker under a hood, add 3 ml of water and 3 ml of
HNO3(Sp.gr.1.42), and cover the beaker with a watch glass. After the metal
hascompletely dissolved add 1ml of H2SO4 (Sp.gr.1.84) and heat on a hot plate
just short of complete dryness. Do not bake the residue. Cool the residue, wash
down the sides of the beaker and the bottom of the watch glass, and again evaporate
the solution nearly to dryness to expel the HN03- Cool the residue, dissolve it in
water, and dilute the solution to 1 litre. Make the standard as needed by diluting
100ml. of the prepared solution to I litre with water. One millilitre of the standard
contains 0.02 mg Cu or when diluted to 50 ml. with water it represents a
0.4 mg/litre (ppm) Cu solution.
ii) Copper, Standard Solution (1 ml = 4 mg Cu ) dilute 200 ml of copper solution
(1ml=0.02 mg Cu) to I litre with water. One millilitre of this standard solution contains
4 mg of copper or, when diluted to 200 ml with water, it contains 20mg /litre(ppb).
Concentrated hydrochloric acid (HCl).
iii) Hydroxylamine hydrochloride Solution (200 g/litre). Remove traces of copper from
the solution prepared by treating in a separatory funnel with neocuproine solution
and isoamyl Alcohol solvent in accordance with procedure. Discard the organic
extract.
iv) Isoamyl Alcohol.
v) Isopropyl Alcohol.
vi) Neocuproine solution (1g/litre)-Dissolve 0.1 9 of neocuproine (2,9 dimethy 1 -1,10 - phenanthroline) in 50 ml. of isopropyl alcohol.Dilute the solution to 100 ml with
water.
vii) Sodium acetate Solution (275 g/litre-Dissolve 55 g of sodium accetate trihydrate,
(CH3
COONa 3H2O) in water and dilute to 200 ml. Remove traces of copper
from the solution by treating in a separatory funnel with NH2
OH. HCl, neocuproine,
and isoamyl alcohol solvent solutions in accordance procedure. Discard the organic
extract.
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* NOTE : Copper analysis should be run prior to iron. The copper in boiler feedwater
is generally in the form of the soluble copper - ammonium complex and the acidified
sample (approximately pH 1.5) will prevent plating out of elemental copper. The preliminary
digestion step in the above procedure will generally assume complete solubility of low
concentrations of copper (less than 50 ppb.)
18.5. APPARATUS REQUIRED
- 500 ml glass bottles with plastic caps with sample extraction hose.
- 250 ml - separating funnels
- 1 ml pipette (for 1:1 HCI)
- 1 ml pipette (for NH2
OH. HCl)
- 10 ml pipette (CH3
COONa solution)
- 2 ml and 4 ml pipettes (for neocuproine)
- 25 ml graduate (for isomyl alcohol)
- 10 ml graduate (for isoprophyl alcohol)
- Spectrophotometer
1.0 cm cell 20 to 1000 ppb
10.0 cm cell 2 to 100 ppb
- Waterbath suitable for heating (Thermostat).
18.6 PROCEDURE
i) Place acidified sample bottle (with top off) in a hot water bath at 900o C for one
hour (See Note)
ii) Cool to room temperature and transfer 200 ml of the sample to a 250ml separatory
funnel.
iii) Add 1 ml of NH2
OH.HCl solution and mix by shaking.
iv) Add 10 ml of CH3
COONa solution and mix again.
V) Then add 2 ml of neocuproine solution (4 ml for greater than 100g of Cu in
sample). Mix by shaking. Allow to stand for about 3 min.
vi) Add 25 ml of isoamyl alcohol and shake for one minute. Allow to stand five minutes
and permit aqueous phase to separate from alcohol phase. Alcohol phase will be at
top and aqueous phase can be drained off.
vii) Collect alcohol layer and add 10 ml of isopropyl alcohol to clear solution. Swirl to
mix thoroughly.
viii) Read in the appropriate cell at 454 nm.
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19. DETERMINATION OF AMMONIA
19.1 SUMMARY OF METHOD
A sample aliquot is Nesslerised directly and ammonia content determined colorimetrically.
Turbid samples may be clarified with ZnSO4 and NaOH. The precipitated Zn (OH)2 is
filtered or centrifuged off and the ammonia is determined on clear aliquot by direct
Nesslerization.
19.2 REAGENTS
i) Ammonium Chloride - Standard Solution A
Dissolve 3.819 g of anhydrous ammonium chloride NH4
Cl, dried at 105o C and
diluted to 1000 ml. (1.0 ml.=1.00 mg N = 1.22 mg NH3).
ii) Standard Solution B
Take 10 ml of solution A and dilute to 1000 ml.
(1.0 ml.= 10.0 mg N = 12.2 mg NH3)
iii) Nessler Reagent
Dissolve 100 g of anhydrous HgI2
and 70 g of anhydrous KI in a small volume of
water, and add this mixture slowly, with stirring, to acooled solution of 160 g of
NaOH in 500 ml of water. Dilute the mixture to1 litre. If this reagent is stored in a
chemically resistant bottle out of direct sunlight, it will remain stable up to a period
of 1 year.
iv) Sodium Hydroxide Solution - 250 g per litre
Dissolve 250 g of NaOH in water, and dilute to 1 litre.
v) Sodium Potassium Tartrate Solution 500 g per litre
Dissolve 500 g of sodium potassium tartrate tetrahydrate in 1 litre of water. Boil
until ammonia-free, and dilute to 1litre.
vi) Zinc Sulphate Solution (100 g per litre)
Dissolve 100 g of ZnSO4