Orion Cupric Electrode - University of Utahring/Instrumental...separate reference electrode is unnecessary, making it convenient to use with small sample volumes. The free-flowing

Analyze • Detect • Measure • Control™

Orion 94-2996-29 ionplus®

Orion CupricElectrode

INSTRUCTION MANUAL

Cu2+

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ionplus electrodes and Optimum Results solutions are protected by US Patent 5,830,338.

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© Copyright 2003, Thermo Electron Corporation. All rights reserved. Question everything, and Analyze.Detect.Measure.Control are trademarks of Thermo Electron Corporation.

The specifications, descriptions, drawings, ordering information and part numbers within this document are subject to change without notice.

This publication supersedes all previous publications on this subject.

TABLE OF CONTENTS

General Information 1 Introduction 1 Required Equipment 2Required Solutions 3

Before Using The Electrode 5 Electrode Preparation 5 Checking Electrode Operation (Slope) 7

Helpful Information 8 Units of Measurement 8Sample Requirements 8 GLP Measuring Hints 9

Choosing the Right Measuring Technique 11

Measurement Procedures 14Direct Measurement 14Small Volume Direct Measurement 18Low-Level Measurements 21Known Addition 25Titration 32Indicator Titrations 34

Electrode Storage 36

Electrode Maintenance 37

Troubleshooting 40 Troubleshooting Checklist 40Troubleshooting Guide 44

Electrode Characteristics 47 Electrode Response 47Limits of Detection 47Reproducibility 47Temperature Effects 48Interferences 49pH Effects 50Complexation 50Theory of Operation 51

Warranty 55

Ordering Information 59

Specifications 60

General Information

Introduction

The Orion 94-29 Cupric Half-Cell Electrode and Orion 96-29ionplus® Series Cupric Electrode measure cupric ions in aqueoussolutions quickly, simply, accurately, and economically.

The 96-29 offers additional benefits of the ionplus Series from theSure-Flow® Combination reference design. With this electrode, aseparate reference electrode is unnecessary, making it convenient touse with small sample volumes. The free-flowing liquid junctionassures stable, drift-free potentials. When measuring dirty sampleswhich would clogconventional electrode junctions, the Sure-Flowjunction can be opened and flushed clean simply by pressing thecap. The Orion 900200 Double Junction Reference electrode, whenused with the 94-29 Cupric Half-Cell Electrode, also offers thebenefits of the Sure-Flow junction design.

General analytical procedures, required solutions, electrodecharacteristics, and electrode theory are discussed in this manual.Operator instructions for Orion meters are given in the meterinstruction manual.

Orion Technical Service Chemists can be consulted for assistance and troubleshooting advice. Please refer toTroubleshooting for information on contacting Orion.

1

Required Equipment

Meter – The easiest to use are direct concentration readout specificion meters (ISE meters), such as Orions EA 940, 920A, 720A, 710A,or 290A. If unavailable, a pH/mV meter with readability to 0.1 mV,such as Orions 420A, 520A, or 525A is recommended.

Reference Electrode Orion

For use with Orion 94-29:Orion 90-02 Double Junction Reference Electrode, includes: 900200

Inner Chamber Filling Solution 900002Outer Chamber Filling Solution 900003

For use with Orion 96-29:The Orion 96-29 ionplus® Series Electrode does not require a separate reference electrode.

Magnetic Stirrer, Stir Bars – Recommended for laboratory measurements.

Graph Paper – 4 cycle semi-logarithmic paper for preparingcalibration curves (for use with pH/mV laboratory meters).

Plastic Labware – For low-level cupric measurements.

Polishing Strips – Orion 948201. To clean the cupric sensing element.

2

Required Solutions

Distilled or Deionized Water – To prepare all solutions and standards.

Reference Filling Solution Orion

Optimum Results™ D 900063 (for Orion 96-29 Combination Cupric Electrode)

Inner Chamber Filling Solution 900002 (for use with Orion 90-02 Reference Electrode)

Outer Chamber Filling Solution 900003 (for use with Orion 90-02 Reference Electrode)

Standard Solutions Orion

0.1 M Cupric Activity Standard 942906

1000 ppm Cupric Customer Concentration Standard Prepared

(see next page)

EDTA Titrant CustomerPrepared(see next page)

Ionic Strength Adjustor (ISA) 940011 To adjust ionic strength of samples and standards, 5M NaNO3

3

Customer Prepared Solutions

1000 ppm Cu2+ solutionPipet 157.4 mL of 0.1 M standard (Orion 942906) in a 1-liter volumetric flask. Dilute to volume with distilled water.

EDTA TitrantRequired ChemicalsTetrasodium EDTA (Na4EDTA), reagent gradeDistilled waterPreparation:1 M stock solution: place 38.0 g reagent Na4EDTA in a 100 mL volumetric flask and dissolve in about 75 mL distilled water. Dilute to volume with distilled water.

4

Before Using The Electrode

Electrode Preparation

Orion 94-29 – Cupric ElectrodeRemove the rubber cap covering the electrode tip.

Orion 90-02 Double Junction Reference ElectrodeFill this reference electrode according to the instructions in thereference electrode instruction manual. Fill the inner chamber withOrion 900002 Filling Solution. Fill the outer chamber with Orion900003 Filling Solution.

Add filling solution each day before using the electrode. The fillingsolution level should be at least one inch above the level of samplein the beaker to ensure a proper flow rate. If the filling solution isless than one inch above the sample solution level, electrodepotentials may be erratic.

Orion 96-29 – ionplus® Series Cupric ElectrodeOrion offers a line of filling solutions designed specifically for yourapplication. Optimum Results™ D (Orion 900063) supplied with thiselectrode is designed to minimize junction potentials and provideoptimum temperature and time response. It can be used for allcupric measurements.

Add filling solution each day before using the electrode. The fillingsolution level should be at least one inch above the level of samplein the beaker to ensure a proper flow rate. If the filling solution isless than one inch above the sample solution level, electrodepotentials may be erratic.

5

The electrode is shipped without filling solution in the referencechamber. To fill from the flip-spout bottle:

1. Lift the spout to a vertical position.

2. Insert the spout into the fill hole in the outer sleeve and add asmall amount of filling solution to the chamber. Tip the electrodeto moisten the O-ring at the top and return electrode to a vertical position.

3. Holding the electrode by the barrel with one hand, use the thumbto push down on the electrode cap, allowing a few drops offilling solution to drain and wet the inner cone.

4. Release sleeve. If sleeve does not return to its original positionimmediately, check to see if the O-ring is moist enough andrepeat steps 2 - 4 until the sleeve has returned to the originalposition. Add filling solution up to the fill hole.

6

Checking Electrode Operation (Slope)

This procedure measures electrode slope. Slope is defined as thechange in millivolts observed with every ten-fold change inconcentration. Obtaining the slope value provides the best meansfor checking electrode performance.

These are general instructions that can be used with most meters tocheck electrode operation. See individual meter instruction manualsfor more specific information.

1. If electrode(s) have been stored dry, prepare the electrode(s) asdescribed in Electrode Preparation.

2. Connect the electrode(s) to the meter as described in the meterinstruction manual. Non Orion meters may require specialadapters. Consult your meter instruction manual.

3. Place 100 mL distilled water into a 150 mL beaker. Add 2 mLISA, ( Orion 940011). Stir thoroughly. Use 0.1 M or 1000 ppm cupric standard in the following steps.

4. Set the meter to the mV mode.

5. Rinse electrode(s) with distilled water, blot dry, and place in thesolution prepared in Step 3 above.

6. Select the appropriate standard. Pipet 1 mL of the standard intothe beaker. Stir thoroughly. When a stable reading is displayed,record the electrode potential in millivolts.

7. Pipet 10 mL of the same standard into the same beaker. Stirthoroughly. When a stable reading is displayed, record theelectrode potential in millivolts.

8. The difference between the first and second potential reading isdefined as the slope of the electrode. The difference should bein the range of (+) 25-30 mV/decade when the solutiontemperature is between 20 and 25 °C. If the slope is not withinthe appropriate range refer to the Troubleshooting section.

7

HELPFUL INFORMATION

Units of Measurement

Cupric ion can be measured in units of moles per liter, parts permillion, or any other convenient unit (see Table 1).

Table 1Concentration Unit Conversion Factors

Moles/Liter g/Liter ppm Cu2+ oz. per gallon

1 63.55 63550 8.491 x 10-3 6.35 x 10-2 63.55 8.49 x 10-3

1.57 x 10-2 1 1000 1.34 x 10-1

1.57 x 10-5 1 x 10-3 1 1.34 x 10-4

1.18 x 10-1 7.489 7489 1

Sample Requirements

The epoxy electrode body is resistant to attack by inorganicsolutions. The electrode may be used intermittently in solutionscontaining methanol or ethanol. Consult Orion Technical ServiceChemists for use of the electrode in other organic solvents (See Assistance).

Samples and standards should be at the same temperature. Forexample, a 1 °C difference in temperature for a 10-3 M solution willgive rise to about a 4% error when using the Orion 94-29. Thecombination cupric electrode, Orion 96-29, when used with theOptimum Results™ D filling solution, produces less than a 2% errorin the same solution. For more information see TemperatureEffects. Temperature must be less than 100 °C.

Cupric samples must be below pH 6 to avoid precipitation ofCu(OH)2. Acidify cupric samples with 1 M HNO3 if necessary. See pH Effects to determine optimum pH working range for your sample.

8

GLP Measuring Hints

See Figure 1

– Stir all standards and samples at a uniform rate duringmeasurement. Magnetic stirrers may generate sufficient heat tochange solution temperature. Place a piece of insulating materialsuch as cork, cardboard, or styrofoam between the stirrer andsample beaker.

– Prepare fresh working standards for calibration daily.

– Always rinse electrode(s) with distilled water betweenmeasurements. Shake after rinsing to prevent solutioncarryover. Blot dry.

– Allow all standards and samples to come to the sametemperature for precise measurement.

– Concentrated samples (> 0.1 M cupric) should be diluted before measurement.

– Measure under constant lighting, as the sensing element mayshow an offset or bias if lighting conditions change markedly.

– After immersion in solution, check electrode(s) for any airbubbles on the sensing element and remove by gently tappingthe electrode(s).

– For high ionic strength samples, prepare standards withcomposition similar to that of the sample.

9

Figure 1GLP Measuring Hints

1 Filling hole should be uncovered (Orions 90-02 and 96-29)

2 Fresh standard

3 Stir all samples and standards

4 Filling solution level must be higher than sample level

5 Reference junction must be immersed

6 Place insulation between stirrer and beaker

10

1

3

4

5

62

CHOOSING THE RIGHT MEASURING TECHNIQUE

A variety of analytical techniques are available to the analyst.

Direct Measurement is a simple procedure for measuring a largenumber of samples. Only one meter reading is required for eachsample. Calibration is performed in a series of standards. Theconcentration of the samples is determined by comparison to thestandards. ISA is added to all solutions to ensure that samples andstandards have similar ionic strength and proper pH. Whenmeasuring small sample volumes or to reduce chemical usage, aspecial Small Volume Direct Measurement method is available usingthe Orion 96-29 ionplus® Series Cupric Electrode.

Low-Level Measurement is a similar method as DirectMeasurement. This method is recommended when the expectedsample concentration is less than 0.6 ppm or 10-5 M Cu2+. Aminimum three point calibration is recommended to compensate forthe electrode’s non-linear response at these concentrations. Aspecial calibration standard preparation procedure describes thebest means of preparing low-level calibration standards.

Known Addition is a useful method for measuring samples, sincecalibration is not required. This method is recommended whenmeasuring only a few samples, or when samples have a high (> 0.1 M) ionic strength, or a complicated background matrix.Refer to Theory of Operation for explanation of these effects. Theelectrodes are immersed in the sample solution and an aliquot of astandard solution containing the measured species is added to thesample. From the change in potential before and after the addition,the original sample concentration is determined. As in directcalibration, any convenient concentration unit can be used.

11

Table 2 Recommended measuring techniques

Small VolumeDirect Direct Low-Level

Measurement Measurement Measurement

[Cu2+] √< 0.6 ppm

[Cu2+] √> 0.6 ppm

[Cu2+] √> 1.0 ppm

Increasedaccuracy

Occasionalsampling

Small sample √volume

Large # of √ √samples

Reduce √Chemical usage

Field √Measurements

Ionic strength> 0.1M

Other metalanalysis

See page # 14 18 21

Titrations are quantitative analytical techniques for measuring theconcentration of a species by incremental addition of a reagent(titrant) that reacts with the sample species. Sensing electrodescan be used for determination of the titration end point. Ion-selective electrodes are useful as end point detectors, becausethey are unaffected by sample color or turbidity. Titrations areapproximately 10 times more precise than direct calibration, but aremore time-consuming.

12

Known IndicatorAddition Titration Titration

[Cu2+] < 0.6 ppm

[Cu2+] √ √> 0.6 ppm

[Cu2+] > 1.0 ppm

Increased √accuracy

Occasional √sampling

Small sample √volume

Large # of √samples

Reduce Chemical usage

Field Measurements

Ionic strength √> 0.1M

Other metal √analysis

See page # 25 32 34

Indicator Titration Method is useful for measuring ionic specieswhere an ion specific electrode does not exist. With this methodthe electrodes sense a reagent species that has been added to thesample before titration. The cupric electrode may be used inindicator titrations for many different metal ions.

13

MEASUREMENT PROCEDURES

Direct Measurement

The following direct measurement procedures are recommended for“high-level” measurements. All samples must be in the electrode’slinear range, greater than 0.6 ppm or 10-5 M Cu2+. A two pointcalibration is sufficient, though more points can be used if desired.With ISE meters, such as the Orions 920A, 720A, 710A, or 290A,sample concentrations can be read directly from the meter. Referto the meter instruction manual for calibration details. When usinga mV meter, a calibration curve can be prepared on semi-logarithmic graph paper, or a linear regression (against logarithmicconcentration values) can be performed at the user’s discretionusing a spreadsheet or graphing program.

Measuring Hints

– Standard concentrations should bracket the expected sample concentrations.

– Always add 2 mL ISA ( Orion 940011) per 100 mL of cupric standard or sample.

– For high ionic strength samples, having an ionic strength of 0.1 M or greater, prepare standards with a composition similarto that of the samples, or measure the samples using the knownaddition method.

– During calibration, measure the least concentrated standard first,and work up to the most concentrated.

– The best method for preparation of standards is by serialdilution. This procedure involves preparing an initial standardthat is diluted, using volumetric glassware, to prepare a secondstandard solution. The second is similarly diluted to prepare athird standard, and so on, until the desired range of standardshas been prepared.

– Verify this procedure by measuring a standard of knownconcentration as an unknown, or by spiking a sample with cupric standard.

– Review section entitled GLP Measuring Hints.

14

Direct Measurement Procedure using ISE Meter

See individual meter instruction manuals for morespecific calibration information.

1. Prepare electrode(s) as described in Electrode Preparation.

2. Connect electrode(s) to the meter, and adjust the meter tomeasure concentration.

3. Prepare at least two standards that bracket the expected samplerange and differ in concentration by a factor of ten. Standardscan be prepared in any concentration unit to suit the particularanalysis requirement. All standards should be at the sametemperature as the samples. For details on temperature effectson electrode performance, refer to Temperature Effects.

4. Measure 100 mL of each standard and sample into separate 150 mL beakers. Add 2 mL ISA to each beaker.

NOTE: Other solution volumes may be used, as long as theratio of solution to ISA remains 50:1.

Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into thebeaker containing the most dilute standard. Wait for a stablereading, then calibrate the meter to display the value of thestandard as described in the meter instruction manual.

6. Rinse electrode(s) with distilled water, blot dry, and place intothe beaker with the next standard. Wait for a stable reading, thenadjust the meter to display the value of this standard, asdescribed in the meter instruction manual.

7. Repeat step 6 for all standards, working from the leastconcentrated to most concentrated standard.

8. Rinse electrode(s) with distilled water, blot dry, and place intosample. The concentration will be displayed on the meter.

15

Figure 2Typical Cupric Calibration Curve

In the direct measurement procedure, a calibration curve isconstructed on semi-logarithmic paper. Electrode potentials ofstandard solutions are measured and plotted on the linear axisagainst their concentrations on the log axis. In the linear regions ofthe curves, only two standards are needed to determine acalibration curve. In nonlinear regions, more points must be taken.The direct measurement procedures in this manual are given forconcentrations in the region of linear electrode response. Low-levelmeasurement procedures are given for measurements in the non-linear region. This curve is only used as an example. ActualmV values may differ.

16

+140

+120

+100

+80

+60

+40

+20

10-7

0.1 1 10 100 1000

Molarity

ppm Cu++

10-6 10-5 10-4 10-3 10-2

+160

+200

+180

+220

+240

Electrode potential(mV)

28 mV

10-fold change

Direct Measurement Procedure using a meter with mV readout


2. Connect electrode(s) to the meter, and adjust the meter tomeasure mV.

3. Prepare at least two standards that bracket the expected samplerange and differ in concentration by a factor of ten. Standardscan be prepared in any concentration unit to suit the particularanalysis requirement. All standards should be at the sametemperature as the samples. For details on temperature effectson electrode performance, refer to Temperature Effects.

4. Measure 100 mL of each standard and sample into separate 150 mL beakers. Add 2 mL ISA to each beaker.


Stir thoroughly.

5. Rinse electrode(s) with distilled water, blot dry and place into thebeaker containing the most dilute standard. When a stablereading is displayed, record the mV value and correspondingstandard concentration.

6. Rinse electrode(s) with distilled water, blot dry, and place intothe beaker with the next standard. When a stable reading isdisplayed, record the mV value and corresponding standard concentration.


8. Using semi-logarithmic graph paper, prepare a calibration curveby plotting the millivolt values on the linear axis and thestandard concentration values on the logarithmic axis. SeeFigure 2.

9. Rinse electrode(s) with distilled water, blot dry, and place intosample. When a stable reading is displayed, record the mV value.

10.Using the calibration curve prepared in step 8, determine theunknown sample concentration.

17

Small Volume Direct Measurement

Take advantage of special design features available with the Orion96-29 ionplus® Series Cupric Electrode to meet your measuringneeds. Due to the Sure-Flow® reference design, this electrodeallows measurement of small volumes of sample, as little as 5 mL,using the following modified direct measurement procedure.Because less solution volume is used, chemical usage of cupricstandards and ISA is reduced, an added benefit. This method isalso convenient when making field measurements, since the Orion96-29 ionplus Series Cupric Electrode is a combination electrode,not requiring a separate reference electrode. Bring less equipmentinto the field. All samples should be greater than 1 ppm or 1.57 x10-5 M Cu2+. As with the previously described Direct Measurementprocedure, a two point calibration is sufficient, though more pointscan be used if desired. Either a direct concentration meter (ISEmeter) or a pH/mV meter with 0.1 mV resolution can be used. The following procedure recommends using 25 mL of sample.Smaller sample volumes can be used, as long as the final volume of solution is sufficient to cover the bottom of the Orion 96-29 electrode.

Measuring Hints

– Use Orion 96-29 ionplus Series Cupric Electrode.

– Standard concentrations should bracket the expected sample concentrations.

– Always keep the ratio of ISA to solution volume 50 to 1.

– The smallest recommended volume for analysis is 5 mL ofsolution with 0.1 mL of ISA added.

– For high ionic strength samples, having an ionic strength of 0.1 M or greater, prepare standards with a composition similarto that of the samples, or measure the samples using the known addition method.

– During calibration, measure the least concentrated standard first,and work up to the most concentrated.

– Prepare calibration standards using serial dilution.

– Calibrate with the same volume of standard as volume of sampleavailable for analysis.


18

Small Volume Direct Measurement Procedure using ISE Meter

See individual meter instruction manuals for more specificcalibration information.

1. Prepare Orion 96-29 Cupric Electrode as described in Electrode Preparation.

2. Connect Orion 96-29 Cupric Electrode to the meter, and adjustthe meter to measure concentration.

3. Prepare at least two standards that bracket the expected samplerange and differ in concentration by a factor of ten.

4. Measure 25 mL of each standard and sample into separate 50 mL beakers. Add 0.5 mL ISA to each beaker.

NOTE: Other solution volumes may be used, as long as the ratio of solution to ISA remains 50:1.

Stir thoroughly.

5. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dry and place into the beaker containing the most dilutestandard. Wait for a stable reading, then calibrate the meter todisplay the value of the standard as described in the meter instruction manual.

6. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dry,and place into the beaker with the next standard. Wait for astable reading, then adjust the meter to display the value of thisstandard, as described in the meter instruction manual.


8. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dry,and place into sample. The concentration will be displayed onthe meter.

19

Small Volume Direct Measurement Procedure using a meterwith mV readout

1. Prepare Orion 96-29 Cupric Electrode as described in Electrode Preparation.

2. Connect Orion 96-29 Cupric Electrode to the meter, and adjustthe meter to measure mV.

3. Prepare at least two standards that bracket the expected samplerange and differ in concentration by a factor of ten.

4. Measure 25 mL of each standard and sample into separate 50 mL beakers. Add 0.5 mL ISA to each beaker.


Stir thoroughly.

5. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dryand place into the beaker containing the most dilute standard.When a stable reading is displayed, record the mV value andcorresponding standard concentration.

6. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dry,and place into the beaker with the next standard. When a stablereading is displayed, record the mV value and correspondingstandard concentration.


8. Using semi-logarithmic graph paper, prepare a calibration curveby plotting the millivolt values on the linear axis and thestandard concentration values on the logarithmic axis. SeeFigure 2.

9. Rinse Orion 96-29 Cupric Electrode with distilled water, blot dry,and place into sample. When a stable reading is displayed,record the mV value.

10.Using the calibration curve prepared in step 8, determine theunknown sample concentration.

20

Low-Level Measurements

These procedures are for solutions with a cupric concentration ofless than 0.6 ppm or 10-5 M Cu2+, those within the non-linear rangeof the cupric electrode. See Figure 2. In low-level measurements,at least three standards are required for calibration to compensatefor the electrode’s non-linearity.

Measuring Hints

– Use plastic labware for low-level cupric measurements.

– For solutions low in cupric but high in total ionic strength(greater than 10-1 M), perform the same procedure as describedbelow, with one change: prepare a calibration solution with acomposition similar to the sample.

– The choice of standard concentrations is important for obtainingthe best electrode performance and most rapid analysis time.Here are some guidelines:

• Ideally, standard concentrations should bracket the expected sample concentrations.

• When measuring sub-ppm levels with Orions 920A,720A, 710A, or 290A, take advantage of the autoblank feature. It does not require a zero standard, but can perform blank correction as long as the lowest standard concentration is in the non-linear range of the electrode. Electrodes are very slow in the absence of a measurable concentration and a multipoint calibration generally will be less accurate when “zero” is included as a standard. Standard concentrations should be chosen such that the lowest standard value is larger than the blank value obtained, and the second lowest standard should be at least twice that of the lowest. See your A-Series meter instruction manual for additional information on blank correction.

21

• If using an ISE meter, such as the Orion EA 940, that allows a blank solution value to be entered, it is recommended to do so. A blank solution is prepared with the same dilution water and ISA used when preparing calibration standards. This solution corrects for the curves non-linearity as well as for any background ion contamination that might be present in the standard solutions. When a blank value is entered, it represents the zero point of the curve, and each standard is measured against that blank.

• When not using an ISE meter, a calibration curve can be drawn on semi-logarithmic graph paper, or the data can be processed at the discretion of the user by means of a spreadsheet or graphing program with a non-linear curve fitting feature.

• When using an ISE meter, such as the Orions 920A,720A, 710A, or 290A, three calibration points are sufficient. If a calibration curve is prepared manually, additional points may be helpful to facilitate drawing the curve.

– Remember to stir all standards and samples at a uniform rate.

– Typical response time for this electrode is approximately 1minute. Low-level measurements may take longer to stabilize.Wait for 3 minutes or the meter’s “ready” signal, whichevertakes longer, before calibrating the meter or recording the sample value.


22

Low-Level Measurement Procedure using ISE Meter

Follow the above procedure entitled Direct Measurement Procedureusing ISE Meter, except add 1 mL low-level ISA to every 100 mL ofsolution, see below step 4. Use at least three calibration standards.Read the Measuring Hints section on pg. 21 in order to selectappropriate standard concentrations. Refer to the meter instructionmanual for detailed calibration procedures. If not using an Orion920A, 720A, 710A, or 290A with the autoblank feature, preparationof a blank solution is recommended to ensure accurate results.

Low-Level Measurement Procedure using a meter with mVreadout (see Table 3)

Set Up


2. Connect electrode(s) to the meter. Set the meter to read mV.

3. Select a standard solution. Use either a 10 ppm cupric standardor a 10-4 M cupric solution.

To prepare 10 ppm from the 1000 ppm cupric standard, dilute 1mL of the 1000 ppm standard to 100 mL with distilled water.

To prepare 10-4 M from 0.1 M cupric standard, dilute 1 mL 0.1 M standard to 1 liter with distilled water.

4. Prepare a low-level ISA solution by diluting 20 mL of the cupricionic strength adjustor, Orion 940011, to 100 mL with distilled water.

NOTE: use this low-level ISA for low-level measurements only.

Measurement

1. Measure 100 mL distilled water into 150 mL beaker. Add 1 mLlow-level ISA.

2. Rinse electrode(s) with distilled water, blot dry, and place intobeaker. Stir thoroughly.

23

3. Add increments of the 10 ppm or 10-4 M standard to the beakerusing steps outlined in Table 3. Record stable millivolt readingafter each increment. On semi-logarithmic paper, plot theconcentration (log axis) against the millivolt potential (linearaxis). See Figure 2. Prepare a new calibration curve with freshstandards each day.

4. Measure 100 mL of sample into a beaker. Add 1 mL low-levelISA. Rinse the electrode(s) with distilled water, blot dry, andplace into the sample.

5. Stir thoroughly. When a stable reading is displayed, record themV value.

6. Determine the sample concentration corresponding to themeasured potential from the low-level calibration curve.

Table 3Preparing a Calibration Curve For Low-Level Measurementsmaking 10 ppm Cupric additions

GraduatedPipet Added Concentration

Step Size Volume ppm

1 0.1 mL 0.01 mL 0.0012 0.1 mL 0.1 mL 0.0113 1.0 mL 0.9 mL 0.1004 10 mL 6.0 mL 0.662

Preparing a Calibration Curve For Low-Level Measurementsmaking 10-4 M Cupric additions

GraduatedPipet Added Concentration

Step Size Volume ppm

1 0.1 mL 0.01 mL 1.0 x 10-8

2 0.1 mL 0.1 mL 1.1 x 10-7

3 1.0 mL 0.9 mL 1.0 x 10-6

4 10 mL 10 mL 9.9 x 10-6

24

Known Addition

Known addition is a convenient technique for measuring samples inthe linear range, greater than 0.6 ppm Cu2+, because no calibrationcurve is needed. The sample potential is measured before and afteraddition of a standard solution. Many meters, such as the Orion920A, have the known addition algorithms preprogrammed. Thisprogramming allows double standard additions to be made to thesample, thereby allowing the meter to calculate the electrode slopeas well. Having the ability to read the sample concentration directlyfrom the meter is a great convenience and ensures accuracy.

Measuring Hints

– Sample concentration should be known within a factor of three.

– Concentration should approximately double as a result of thefirst standard addition.

– With double or multiple known addition, the final addition shouldbe 10 to 100 times the sample concentration.

– In general, either no complexing agent or a large excess of thecomplexing agent may be present.

– The ratio of the uncomplexed ion to complexed ion must not bechanged by addition of the standard.

– All samples and standards should be at the same temperature.

– Add 2 mL ISA to every 100 mL of sample before analysis.

– Standard addition volume should be no more than 10% of thesample volume, or the standard should be pre-treated with ISAin a 50:1 ratio. See Table 4.


25

Set-up


2. Connect electrode(s) to the meter.

3. Prepare a standard solution that, upon addition to the sample,will cause the concentration of cupric to double. Refer to Table 4 as a guideline.

4. Determine the slope of the electrode by performing theprocedure under Checking Electrode Operation (Slope).

Known Addition Measurement Procedure using an ISE meterwith KA program

See individual meter instruction manual for more specific information.

1. Set the meter to measure in the known addition mode.

2. Measure 100 mL of sample into a beaker. Add 2 mL ISA. Stirthoroughly. Rinse electrodes with distilled water, blot dry, andplace in sample solution.

3. When a stable reading is displayed, program the meter asdescribed in the meter instruction manual.

4. Pipet the appropriate amount of standard solution into thebeaker. Stir thoroughly.

5. When a stable reading is displayed, record the sample concentration.

Table 4Standard Addition volumes

Volume of Addition Concentration of Standard

1 mL 100 x sample concentration5 mL 20 x sample concentration10 mL* 10 x sample concentration

* Most convenient volume to use.

26

Known Addition Measurement Procedure using a meter withmV readout

1. Set the meter to millivolt mode.

2. Measure 100 mL of the sample into a 150 mL beaker. Add 2 mL ISA. Stir thoroughly.

3. Rinse electrodes with distilled water, blot dry, and place intobeaker. When a stable reading is displayed, record the mV value as E1.

4. Pipet the appropriate amount of standard solution into thebeaker. See Table 4. Stir thoroughly.

5. When a stable reading is displayed, record the mV value as E2.Subtract the first reading from the second to find ∆E.

6. From Table 6, find the value Q, that corresponds to the changein potential, ∆E. To determine the original sample concentration,multiply Q by the concentration of the added standard:

Csam = Q*Cstd

where:

Cstd = standard concentrationCsam = sample concentrationQ = reading from known addition table

The table of Q values is calculated for a 10% volume change forelectrodes with slopes 28, 29, 29.6, 30 mV/decade for cupric. Theequation for the calculation of Q for different slopes and volumechanges is given below:

Q = p * r

(1+p)10∆E/S -1

where:

Q = reading from known addition table∆E = E2 - E1S = slope of the electrodep = (volume of standard) / (volume of sample & ISA)r = (volume of sample & ISA) / (volume of sample)

27

If it is more convenient, a simple spreadsheet can be set up tocalculate known addition results, using any ratio of sample toaddition. A typical worksheet is shown in Table 5. The numbersshown are examples, but the formulas and their locations should becopied exactly.

Table 5Calculating known addition for cupric samples using Lotus, Excel,or Quattro Spreadsheet

A B C

1 Enter Value2 Vol. of Sample &

ISA, mL: 1023 Vol. of Addition,

mL: 104 Concentrn. of

Addition: 105 Vol. of Sample 1006 Initial mV Reading 45.37 Final mV Reading -63.78 Electrode Slope 28.2910 Derived Values11 Delta E +C7 - C612 Solution Vol. Ratio +C3/C213 Antilog Term +10^ (C11/C8)14 r Term +C2/C515 Q Term +C12*C14/{[(1+C12)*C13]-1}16 Calculated Initial

Conc. in same units as addition: +C15*C4

NOTE: for Excel, use = instead of + at start of formula

28

Table 6 Known Addition Table for an added volume one-tenth the totalvolume. Slopes, in the column headings, are in units ofmV/decade.

Q, Concentration Ratio(slope)

-∆E 28.6 29.1 29.6 30.1

0.16400.15760.15160.14590.14060.13560.13080.12630.12210.11800.11420.11050.10710.10370.10060.09760.09470.09190.08930.08680.08430.08200.07980.07760.07550.07350.07160.06980.06800.06630.06460.06300.06150.06000.05850.05720.05580.05450.05320.05200.05080.04970.04850.04740.0464

0.16130.15490.14900.14340.13810.13310.12840.12400.11980.11580.11200.10840.10500.10170.09860.09560.09280.09000.08740.08490.08250.08030.07800.07590.07390.07190.07000.06820.06650.06480.06310.06160.06000.05860.05720.05580.05450.05320.05190.05070.04950.04840.04730.04620.0452

0.15850.15220.14630.14080.13560.13070.12600.12170.11750.11360.10980.10630.10290.09970.09660.09360.09080.08820.08560.08310.08080.07850.07630.07420.07220.07030.06840.06660.06490.06330.06170.06010.05860.05720.05580.05440.05310.05180.05060.04940.04830.04720.04610.04500.0440

0.15570.14950.14370.13820.13310.12820.12360.11930.11520.11130.10760.10410.10080.09760.09460.09170.08890.08630.08370.08130.07900.07670.07460.07250.07060.06870.06680.06510.06340.06170.06020.05860.05720.05570.05440.05300.05180.05050.04930.04810.04700.04590.04490.04380.0428

5.05.25.45.65.86.06.26.46.66.87.07.27.47.67.88.08.28.48.68.89.09.29.49.69.810.010.210.410.610.811.011.211.411.611.812.012.212.412.612.813.013.213.413.613.8

29


-∆E 28.6 29.1 29.6 30.1

0.04540.04440.04340.04250.04160.04070.03860.03660.03470.03300.03140.02980.02840.02700.02580.02460.02340.02240.02130.02040.01950.01860.01780.01700.01620.01550.01490.01420.01360.01310.01250.01200.01150.01100.01050.01010.00970.00930.00890.00850.00820.00790.00760.00720.00700.00670.00640.00620.00590.00570.00550.00520.00500.00480.0046

0.04420.04320.04230.04130.04040.03960.03750.03560.03370.03200.03050.02900.02750.02620.02500.02380.02270.02160.02060.01970.01880.01790.01710.01640.01570.01500.01430.01370.01310.01250.01200.01150.01100.01050.01010.00970.00930.00890.00850.00820.00780.00750.00720.00690.00660.00640.00610.00590.00560.00540.00520.00500.00480.00460.0044

0.04300.04210.04110.04020.03930.03850.03650.03450.03280.03110.02950.02810.02670.02540.02420.02300.02190.02090.01990.01900.01810.01730.01650.01580.01510.01440.01380.01320.01260.01200.01150.01100.01060.01010.00970.00930.00890.00850.00810.00780.00750.00720.00690.00660.00630.00610.00580.00560.00530.00510.00490.00470.00450.00430.0042

0.04190.04090.04000.03910.03820.03740.03540.03350.03180.03020.02860.02720.02580.02460.02340.02230.02120.02020.01920.01830.01750.01670.01590.01520.01450.01390.01320.01260.01210.01160.01100.01060.01010.00970.00930.00890.00850.00810.00780.00740.00710.00680.00650.00630.00600.00580.00550.00530.00510.00490.00470.00450.00430.00410.0039

14.014.214.414.614.815.015.516.016.517.017.518.018.519.019.520.020.521.021.522.022.523.023.524.024.525.025.526.026.527.027.528.028.529.029.530.030.531.031.532.032.533.033.534.034.535.035.536.036.537.037.538.038.539.039.5

30


-∆E 28.6 29.1 29.6 30.1

0.00450.00430.00410.00400.00380.00370.00350.00340.00320.00310.00300.00290.00280.00270.00260.00250.00240.00230.00220.00210.00200.00190.00190.00180.00170.00170.00160.00150.00150.00140.00140.00130.00130.00120.00120.00110.00110.00100.00100.00100.0009

0.00420.00410.00390.00370.00360.00350.00330.00320.00310.00290.00280.00270.00260.00250.00240.00230.00220.00210.00210.00200.00190.00180.00180.00170.00160.00160.00150.00140.00140.00130.00130.00120.00120.00110.00110.00110.00100.00100.00090.00090.0009

0.00400.00380.00370.00350.00340.00330.00310.00300.00290.00280.00270.00260.00240.00240.00230.00220.00210.00200.00190.00180.00180.00170.00160.00160.00150.00150.00140.00130.00130.00120.00120.00110.00110.00110.00100.00100.00090.00090.00090.00080.0008

0.00380.00360.00350.00330.00320.00310.00290.00280.00270.00260.00250.00240.00230.00220.00210.00200.00190.00190.00180.00170.00170.00160.00150.00150.00140.00130.00130.00120.00120.00110.00110.00110.00100.00100.00090.00090.00090.00080.00080.00080.0007

40.040.541.041.542.042.543.043.544.044.545.045.546.046.547.047.548.048.549.049.550.050.551.051.552.052.553.053.554.054.555.055.556.056.557.057.558.058.559.059.560.0

31

Titration

The electrode makes a highly sensitive endpoint detector fortitration with EDTA of copper samples. Titrations are more time-consuming than direct electrode measurement, but results are moreaccurate and reproducible. With careful technique, titrationsaccurate to ± 0.1% of the total cupric ion concentration of thesample can be performed. The Orion 960 Autochemistry Systemmay be used to automate these titrations.

EDTA complexes other cations besides cupric ion. Interferencesfrom alkaline earths and other ions, whose EDTA complexes arestable only at high pH, can be eliminated by performing the titrationfor cupric ion at a low pH. In many cases, other interferences canbe eliminated by a suitable choice of sample pH and the addition ofmasking agents to the sample solution. A comprehensive list ofmethods is given in: Handbook of Analytical Chemistry, L. Meites, (ed.) McGraw Hill Book Co., New York, (1st edit.), pp. 3-76, 3-225.

Set-up


2. Connect electrodes to the meter.

3. Prepare an EDTA titrant solution 10 - 20 times as concentratedas the sample by dilution of the 1 M stock solution. For a goodend point break, the sample concentration should be at least 10-3 M in total copper.

32

Measurement

1. Place 50 mL of sample into a 150 mL beaker. Place electrode(s)in the sample. Stir thoroughly.

2. Using a 10 mL burette, add increments of titrant and plotelectrode potential against mL of titrant added. The end point isthe point of greatest slope (inflection point). See Figure 3.

3. Calculate the sample concentration before dilution:

Csam = Ct (Vt/Vsam)

where:

Csam = sample concentrationCt = titrant concentrationVsam = sample volumeVt = titrant volume added at endpoint.

Figure 3Typical Titration of 10-3 CuCl2 with 10-2 M Na4EDTA

33

+20

0

-20

-60

-100

-140

1 3 5 7 9 11 13

mL of 10-2 M Na4EDTA

+60

+220.0

+180.0

+140

+100

potential (mV)

endpoint 10.6

Indicator Titrations

The cupric electrode can be used to detect the end point in titrationsof other metal ions. A small amount of copper complex is added tothe sample, and a complexometric titration is done. The end pointvolume of titrant is used to calculate the sample concentration. Theminimum level of sample ion that can be determined by indicatortitration is above 10-4 M. Table 7 lists several species that can betitrated, with appropriate reagents and titrants.

1. Prepare the 10-2 M reagent by titrating the 0.1 M cupric standardexactly to the end point with a 0.1 M solution of the titrant to beused (see Table 7). Dilute the solution obtained five-fold, usinga volumetric flask, to make the reagent.

2. Prepare a titrant solution about 10 times as concentrated as thesample. Place in a 10 mL buret.

3. Place electrode(s) in 50 to 100 mL of the sample. Recordsample volume. Add 1 mL reagent to the sample. Adjust to pH 9. Stir thoroughly during the titration.

4. Add increments of the titrant and record electrode potential. Plotelectrode potential as a function of titrant volume on linear graphpaper (see Figure 4).

5. Calculate the sample concentration,

Csam = Ct (Vt/Vsam)

where:

Csam = sample concentrationCt = titrant concentrationVsam = sample volumeVt = titrant volume added at endpoint.

34

Table 7 Reagents and Titrants for Indicator Titrations

ReagentSpecies (10-2 M) Titrant

Barium CuCDTA CDTACalcium CuEGTA EGTACobalt (2+) CuEDTA EDTAMagnesium CuEDTA EDTAManganese (2+) CuEDTA EDTANickel CuTEPA TEPAStrontium CuEDTA EDTAVanadium CuEDTA EDTAZinc CuTEPA TEPA

Reference: Chelometric Indicator Titrations with the Solid-StateCupric Ion Selective Electrode, Ross, J.W., and Frant, M.S.; Anal.Chem., 1969, 41(13), 1900.

Figure 4R Titration of 100 mL of 10-3 M Ca++

(CuEDTA indicator added to sample)

35

0

-1000 5

Ca++

+100

mL Na4EDTA added

36

Electrode Storage

Orion 94-29 Cupric Half-Cell Electrode

Orion 94-29 Cupric Half-Cell Electrode should be rinsed thoroughlyand stored in distilled water or in the air at all times. When storingfor long periods of time, replace the cap to protect the sensingelement and store dry.

Orion 96-29 ionplus® Series Cupric Electrode

The solution in the Orion 96-29 Combination Cupric Electrode should not be allowed to evaporate, causing crystallization.

For short periods of time (up to one week):Store the electrode in distilled water.

For storage longer than one week:Drain the electrode, flush the inside with distilled water and storedry with the cap on to protect the sensing element.

Orion 90-02 Double Junction Reference Electrode

Orion 90-02 Reference Electrode may be stored in air betweensample measurements (up to two hours).

For short periods of time (up to one week):90-02 should be stored in outer filling solution. Distilled water isalso an acceptable storage solution. The solutions inside theelectrode should not be allowed to evaporate causing crystallization.

For storage longer than one week: Drain both chambers of the reference electrode, flush the insidewith distilled water, and store dry.

37

Electrode Maintenance

Cupric Electrode Cleaning Procedure

Place a drop of liquid dish detergent on a moist cloth or tissue andgently rub over the sensing element. Rinse with distilled water.

Cupric Electrode Polishing Procedure

To be used when electrode becomes sluggish or drifty and abovecleaning procedure does not improve electrode response.

1. Cut off a 1-inch length of the polishing strip, Orion 948201

2. Hold electrode with the sensing element facing upwards.

3. Place a few drops of distilled water on the sensing element surface.

4. With the frosted side down, place the polishing strip on thesensing element using light finger pressure.

5. Rotate the electrode for about 30 seconds.

6. Rinse and soak in a 1 ppm or 10-5 M cupric standard solution forabout two minutes before use.

38

Disassembly And Cleaning of 96-29 Sure-Flow CombinationCupric Electrode

Disassembly is not normally required or recommended. When thearea between the electrode sleeve and inner cone becomes cloggedwith sample or precipitate from filling solution, the chamber can becleaned by flushing out with filling solution. (Hold the electrode bythe cap with one hand and push the outer sleeve of the electrode upinto the cap to drain the chamber.) If the chamber is not completely clean, repeat the procedure. Refill with the appropriatefilling solution.

If a more thorough cleaning is required, the electrode can bedisassembled using the following instructions:

1. Rinse the outer body under warm running water.

2. Hold the electrode body by the cap with one hand and push the outer sleeve of the electrode up into the cap to drain the chamber.

3. Unscrew the cap, slide the cap and epoxy-coated spring upalong the cable.

4. Hold the outer sleeve with one hand and firmly push down onthe threaded portion with the thumb and forefinger to separatethe inner body from the sleeve.

5. Grasp the cone with a clean tissue and withdraw the body fromthe sleeve with a gentle twisting motion.

NOTE: Do not touch the AgCl pellet above the cone as itmay cause damage to the pellet.

Rinse the outside of the electrode body and the entire sleevewith distilled water. Allow to air dry.

39

Reassemble

1. Moisten the O-ring on the electrode body with a drop of fillingsolution. Insert screw-thread end of the electrode body into thetapered, ground end of sleeve.

2. Push body into sleeve with a gentle twisting motion until bottomsurface of inner cone is flush with the tapered end of the sleeve.

3. Place the spring on the electrode body and screw on the cap.Refill with filling solution. The electrode is now ready for use.

40

TROUBLESHOOTING

Troubleshooting Checklist

Symptom Possible Causes

Defective meterDefective electrode Electrodes not plugged in properly Reference electrode junction is dry

(Orions 96-29 & 90-02)Reference electrode chamber not filled

(Orions 96-29 & 90-02)Air bubble on electrodeElectrodes not in solution

Defective meterMeter or stirrer improperly groundedAir bubble on electrodeWrong reference electrodeISA not used

Samples and standards at different temperatures

Sensing element dirty or etchedIncorrect reference filling solution

Off-scale orOver-rangereading

Noisy or unstablereadings (readingscontinuously orrapidly changing)

Drift (Readingslowly changingin one direction)

41

Solution

Check meter with shorting strap (See meter instruction manual)Refer to Troubleshooting GuideUnplug electrodes and reseat Hold reference electrode and push cap to expel a few drops of

filling solution Be sure reference electrode chamber is filled.

See Electrode PreparationRemove air bubble on electrode by gently tapping it.

Put electrodes in solution

Check meter with shorting strap (See meter instruction manual)Check meter and stirrer for grounding See Using the Electrode Remove air bubble on electrode by gently tapping it.Use appropriate reference electrode. See Required EquipmentDo not use calomel or Ag/AgCl (frit-or fiber-type)

reference electrode Use recommended ISA

Allow solutions to come to room temperature before measurement

Polish sensing element (see Electrode Maintenance)Use recommended filling solution. See Required Solutions

42

Troubleshooting Checklist (cont.)

Symptom Possible Causes

Electrodes not properly conditionedStandards contaminated or

incorrectly madeISA not usedStandard used as ISAElectrode exposed to interferences

Incorrect scaling of semilog paper Incorrect signIncorrect standardsWrong units usedComplexing agents in sample

Low slope orNo slope

“Wrong Answer”(But calibrationcurve is OK)

43

Solution

Prepare fresh standards Use recommended ISAUse ISA! Refer to Troubleshooting Guide

Plot millivolts on the linear axis. On the log axis, be sure concentration numbers within each decade are increasing with increasing concentration

Be sure to note sign of millivolt value correctlyPrepare fresh standardsApply correct conversion factor: 10-3 M = 63.5 ppm as Cu2+

Use known addition or titration techniques, or a decomplexing procedure

For additional information on blank correction with your A-Series meter, see your meter operations manual

44

Troubleshooting Guide

The most important principle in troubleshooting is to isolate thecomponents of the system and check each in turn. The componentsof the system are: 1) Meter 2) Electrodes 3) Standard 4) Sampleand 5) Technique.

See also GLP Measuring Hints section.

Meter

The meter is the easiest component to eliminate as a possible causeof error. Orion meters are provided with an instrument checkoutprocedure in the instruction manual and a shorting cap forconvenience in troubleshooting. Consult the manual for completeinstructions and verify that the instrument operates as indicated andis stable in all steps.

Electrodes

1. Rinse electrode(s) thoroughly with distilled water.

2. Determine electrode slope. See Check Electrode Operation.

3. If electrode fails this procedure, prepare electrode(s) as directedin Electrode Preparation. Clean electrode(s) as described inElectrode Maintenance.

4. Repeat step 2, Checking Electrode Operation.

5a.For the 94-29 Cupric Half-Cell Electrode:If the electrodes still do not perform as described, determinewhether the cupric or reference electrode is at fault. To do this,substitute a known working electrode for the electrode inquestion and repeat the slope check.

5b.For the 96-29 ionplus® Series Cupric Electrode:If the electrode still does not perform as described replace the electrode.

6. If the stability and slope check out properly, but measurementproblems persist, the sample may contain interferences orcomplexing agents, or the technique may be in error. SeeStandard, Sample, and Technique sections.

45

7. Before replacing a “faulty” electrode, or if another electrode isnot available for test purposes, review the instruction manualand be sure to:

- Clean the electrode thoroughly- Prepare the electrode properly- Use proper filling solution, ISA, and standards- Measure correctly- Review Troubleshooting Checklist

Standard

The quality of results depends greatly upon the quality of thestandards. ALWAYS prepare fresh standards when problems arise –it could save hours of frustrating troubleshooting! Error may resultfrom contamination of prepared standards, quality distilled water, ora numerical error in calculating the concentrations.

The best method for preparation of standards is by serial dilution.This means that an initial standard is diluted, using volumetricglassware, to prepare a second standard solution. The second issimilarly diluted to prepare a third standard, and so on, until thedesired range of standards has been prepared.

Sample

If the electrodes work properly in standards but not in sample, lookfor possible interferences, complexing agents, or substances thatcould affect response or physically damage the sensing electrode orthe reference electrode. If possible, determine the composition ofthe samples and check for problems. See Sample Requirements,Interferences, and pH Effects.

Technique

Check the method of analysis for compatibility with your sample.Direct measurement may not always be the method of choice. If alarge amount of complexing agents is present, or if the sample hasa high ionic strength, known addition may be best. If working at lowlevels, be sure to follow the low-level measurement technique. Also,be sure that the expected concentration of the ion of interest iswithin the electrode’s limits of detection. If problems persist, reviewoperational procedures and instruction manuals to be sure thatproper technique has been followed. Read Measuring Hints,Analytical Procedures, and Electrode Characteristics.

46

After troubleshooting all components of your measurement system,contact The Technical EdgeSM for Orion products. Within theUnited States call 1.800.225.1480, outside the United States call978.232.6000 or fax 978.232.6031. In Europe, the Middle East andAfrica, contact your local authorized dealer. For the most currentcontact information, visit www.thermo.com.

47

ELECTRODE CHARACTERISTICS

Electrode Response

The electrode potential plotted against cupric concentration onsemi-logarithmic paper results in a straight line until concentrationreaches 10-5 M, with a slope of about (+) 25 to 30 mV per decade(see Figure 5). The electrode exhibits good time response (99%response to one minute or less) for concentrations above 10-5 M.Below this value response times vary from 2 to 5 minutes.

Figure 5Typical Electrode Response to Step Changes in Cu(NO3)2

Limits of Detection

In neutral solutions, cupric ion concentrations can be measureddown to 10-8 M (6 x 10-4 ppm). Extreme care must be taken inmaking determinations below 10-5 M (0.6 ppm) to avoid samplecontamination or adsorption of cupric ion on container walls.

Reproducibility

Reproducibility is limited by factors such as temperaturefluctuations, drift and noise. Because the electrode exhibitslogarithmic results, the precision is independent of concentration.With calibration every hour, direct electrode measurementsreproducible to ± 4% can be obtained.

Electrode potential (mV)

+225

+125

+100

+75

0 1.0 1.5 2.0 2.5 3.00.5

time (minutes)

10-3 to 10-2 M Cu(NO3)2

10-3 to 10-4 M Cu(NO3)2

10-3 to 10-7 M Cu(NO3)2

10-3 to 10-6 M Cu(NO3)2

10-3 to 10-5 M Cu(NO3)2+150

+200

+250

+175

48

Temperature Effects

Since the electrode potentials are affected by changes intemperature, samples and standard solutions should be within ± 1 °C (± 2 °F) of each other. At the 10-3 M level, a 1 °C differencein temperature results in a 4% error. The absolute potential of thereference electrode changes slowly with temperature because of thesolubility equilibria on which the electrode depends. The slope ofthe electrode also varies with temperature, as indicated by the “S”in the Nernst equation, see Theory of Operation. Theoretical valuesof the slope at different temperatures are given in Table 8. Iftemperature changes occur, meter and electrodes should be recalibrated.

The electrode can be used at temperatures from 0° to 100 °C,provided that temperature equilibrium has occurred. For use attemperatures substantially different from room temperature,calibration standards should be at the same temperature assamples. The electrode should be used only intermittently attemperatures above 80 °C.

Table 8Theoretical Values of Electrode Slope vs. Temperature

°C Slope (Cu2+)

0 27.110 28.120 29.125 29.630 30.140 31.150 32.1

If sample temperatures vary, use of the 96-29 ionplus® SeriesCupric Electrode is recommended. The Optimum Results™ D FillingSolution, provided with this electrode, will minimize junctionpotentials and provide optimum temperature and time response.

49

Interferences

Mercury and silver ion poison the cupric electrode sensing elementand must be absent from the sample solution. Exposure to either ofthese species at levels greater than 10-7 M will require polishing ofthe electrode surface. Ferric ion affects the sensing element only ifthe ferric ion level is greater than one tenth of cupric ion level (ferricion can be eliminated from the sample simply by adding sodiumfluoride and adjust to pH 4 - 6).

If the electrode is exposed to high levels of interfering ions, it may become unstable and sluggish in response. When thishappens, restore normal performance by polishing (see Electrode Maintenance).

In some cases chloride and bromide ion interfere with electrodeoperation. Interference is dependent on the level of chloride orbromide ion relative to the level of cupric ion in the sample andoccurs only if the concentrations (in moles per liter) are outside the limits:

(Cu2+)(Cl-)2 > 1.6 x 10-6

(Cu2+)(Br-)2 > 1.3 x 10-12

Figure 6 shows the regions above the lines in which cupric ion and chloride or bromide ion levels are high enough to causeelectrode malfunction.

Figure 6Interference From Chloride And Bromide Ion

10-6 10-5 10-4 10-3

Cu++ (M)10-2 10-1 1 10

Cl-

or B

r- (M

)

10-1

1

10-2

10-3

10-4

Cl- interference

Br- interference

50

pH Effects

The formation of insoluble Cu(OH)2 limits the pH range over whichcupric ion measurements can be made. Figure 7 shows the effectsof OH- in solutions of various cupric ion concentrations. Theshaded region indicates the pH range in which the hydroxide ionconcentration is high enough to cause precipitation of Cu(OH)2,reducing the level of free cupric ion in the sample. As the figureindicates, the greater the cupric ion concentration, the lower the pHin which cupric hydroxide precipitates. Adjusting sample andstandard pH below 6 avoids hydroxide precipitation.

Complexation

Cupric forms complexes with a wide variety of species includingacetate, ammonia and organic amines, citrate, amino acids, andEDTA. The extent of complexation depends on the concentration ofcupric and complexing agent, and pH. Since the electrode onlyresponds to free cupric ions, complexation reduces the measuredconcentration. In a large excess (50 to 100 times) of a complexingagent, total cupric concentration can be measured by known addition.

Soluble cupric salts are precipitated by sulfide, phosphate,hydroxide, and other ions. The formation of a precipitate dependson the level of cupric ion, the level of the precipitating ion in thesample solution, and the solution pH.

51

Figure 7Precipitation of Cupric Ion by Hydroxide Ion

Theory of Operation

The cupric electrode includes a cupric sensing element bonded into anepoxy body. When the sensing element is in contact with a solutioncontaining cupric ions an electrode potential develops across thesensing element. This potential, which depends on the level of freecupric ion in solution, is measured against a constant referencepotential with a pH/mV meter or specific ion meter. The measuredpotential, corresponding to the level of cupric ion in solution, isdescribed by the Nernst equation:

10-2 M Cu++

10-3 M Cu++

10-4 M Cu++

pH

0 1 2 3 4 5 6 7 8

+40

+50

+60

+70

+80

+90

+100

+110

+120

+130

electrode potential (mV)

Cu(OH)2

precipitation

52

E = E0 + S log (A)

where:

E = measured electrode potential E0 = reference potential (a constant)A = level of cupric ion in solution S = electrode slope (about 28 mV per decade for cupric)

S = 2.3 R T

nF where: R & F are constantsT = temperature degrees Kn = ionic charge (+2)

The ionic level, A, is the activity or “effective concentration”. Thecupric ion activity is related to free-ion concentration, Cf, by theactivity coefficient, y:

A = y*Cf

The copper electrode measures copper activity in the same way as apH electrode measures hydrogen ion activity. This can be useful inthe study of biological effects and in understanding copperspeciation. To measure copper ion activity, copper standards areassigned activity values, and no ISE or pH adjustments are made tothe samples. Estimated copper activities for the cupric nitratestandard are given below. For other cupric solutions, the presenceof other species will affect the ion activity.

Table 9Concentration and activity values of cupric nitrate standardizing solutions at 25 °C.

concentration (M) activity (M)

10-1 3.2 x 10-2

5 x 10-2 9.6 x 10-3

10-2 5.5 x 10-3

5 x 10-3 1.4 x 10-3

10-3 7.9 x 10-4

10-4 9.2 x 10-5

10-5 10-5

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Ionic activity coefficients are variable and largely depend on totalionic strength. The ionic strength of a solution is determined by allof the ions present. It is calculated by multiplying the concentrationof each individual ion by the square of its charge, adding all thesevalues up, and then dividing by two.

Ionic strength is defined as:

I = 1/2 ∑(CiZi2)

where:

Ci = concentration of ion i Zi = charge of ion iS = symbolizes the sum of all the types of ions

in solution.

If the background ionic strength is high and constant relative to thesensed-ion concentration, the activity coefficient is constant andactivity is directly proportional to concentration. Ionic strengthadjustor (ISA) is added to all standards and samples so that thebackground ionic strength is high and constant relative to variableconcentrations of cupric. For cupric, the recommended ISA isNaNO3. Other solutions can be used as long as they do not containions that would interfere with the electrode’s response to cupric. Ifsamples have a high ionic strength (above 0.1 M), standards shouldbe prepared with a composition similar to the samples.

Reference electrode conditions must also be considered. Liquid-junction potentials arise any time two solutions of differentcomposition are brought into contact. The potential results from theinterdiffusion of ions in the two solutions. Since ions diffuse atdifferent rates, electrode charge will be carried unequally across the solution boundary resulting in a potential difference between the two solutions. In making electrode measurements, it isimportant that this potential be the same in the standardizingsolution as in the sample solution; otherwise, the change in liquid-junction potential will appear as an error in the measured electrode potential.

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Optimum Results™ filling solutions are specifically designed to meetall reference electrode conditions. The filling solution isequitransferent. Therefore, the speed with which the positive andnegative ions in the filling solution diffuse into the sample is asnearly equal as possible. If the rate at which positive and negativecharge is carried into the sample solution is equal, then minimumjunction potential can result.

55

WARRANTY

For the most current warranty information, visit www.thermo.com.

The Thermo Electron Corporation, Orion products warranty coversfailures due to manufacturer’s workmanship or material defectsfrom the date of purchase by the user. User should return thewarranty card and retain proof of purchase. Warranty is void ifproduct has been abused, misused, or repairs attempted byunauthorized persons.

Warranties herein are for product sold/installed by Thermo or itsauthorized dealers.

Any product sold by a U.S. or Canadian distributor must bereturned to Thermo for any warranty work. Please contact ourTechnical Service department for further information. A ReturnAuthorization Number must be obtained from The Technical EDGESM

for Orion Products before returning any product for in-warrantyrepair or replacement.

In the event of failure within the warranty period, Thermo will at thecompany’s option, repair or replace product not conforming to thiswarranty. There may be additional charges, including freight, forwarranty service performed in some countries. For service, callThermo or its authorized dealer outside the United States andCanada. Thermo reserves the right to ask for proof of purchase,such as the original invoice or packing slip.

Field Service is available on Orion BOD AutoEZ™, EZ Flash® GCAccessory and TEA Analyzer®. Contact our Field Service departmentfor details on quotations, service and other field service-relatedactivities.

The following products are warranted to be free from defects inmaterial and workmanship in the period listed below from the dateof purchase from the user or from the date of shipment fromThermo, whichever is earlier, provided use is in accordance with theoperating limitations and maintenance procedures in the instructionmanual and when not having been subjected to accident, alteration,misuse, abuse or breakage of electrodes:

Thirty-six months from date of purchase by the user (or forty-twomonths from date of shipment from Thermo)

• Waterproof Meters (Orion 630, 635, 830A, 835A, 260A, 261S,265A, 266S, 130A, 131S, 135A and 136S), Conductivity Meters(Orion 105Aplus, 115Aplus, 125Aplus, 145Aplus, 150Aplus and162A), PerpHect® pH/ISE Meters (Orion 310, 320, 330, 350,370) pH/ISE Meters (Orion 210Aplus, 230Aplus, 250Aplus,290Aplus, 410Aplus, 420Aplus, 520Aplus, 525Aplus, 710Aplus,

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720Aplus and 920Aplus), pHuture MMS™ Meters (Orion 535Aand 555A), pH/Conductivity Meter (Orion 550A), DissolvedOxygen Meters (Orion 805Aplus, 810Aplus, 850Aplus and862A).

Twenty-four months from date of purchase by the user (or thirty-six months from date of shipment from Thermo)

• Orion ROSS Ultra® Electrodes, Orion AQUAfast® IVColorimeters, Orion AQUAfast® IV Turbidimeter, Orion 925Flash Titrator™, Series 100 DuraProbe™ Conductivity Cells andSeries 800 Dissolved Oxygen Probes.

Twelve months from date of purchase by the user (or eighteenmonths from date of shipment from Thermo)

• Laboratory pH Meters, (Orion 301, 611 and 940), SensorLink®,pHuture™ pH Meters (Orion 610 and 620), Sage® Pumps,Cahn® Balances, 930 Ionalyzer®, 950 ROSS™ FAST QC™

Titrator, 960 Titrator PLUS®, Karl Fischer Titrators,Autosamplers, Liquid Handling Devices, Liquid HandlingAutomation Workstations (Orion AS2000, AS2500 andAS4000), Pumps (Orion SP201, SP201-HR, SP201-S,Peristaltic and Rinse), pHuture® Conversion Box, WineMaster®, 607 Switchbox, rf link™, AQUAfast® II Colorimeters,Vacuum Degasser and Flowmeter.

• Orion EZ Flash® GC Accessory, Orion TEA Analyzer® 610 and510 excluding consumable items carry twelve months warrantyonly.

• Orion Ion Selective Electrodes, ionplus® Electrodes, ROSS™

Electrodes, Sure-Flow® Electrodes, PerpHecT® Electrodes,AquaPro Professional Electrodes, No Cal™ pH electrodes,Standard Line pH Electrodes, Tris pH Electrodes, KNIpHE®

electrode, ORP Triode™ (Orion 9180BN), pHuture™ pH Probes(Orion 616500) and pHuture MMS™ Quatrode™ and Triode™

(Orion 616600 and 617900), Orion 97-08 DO Probe, Series 100Conventional Conductivity Cells, temperature probes andcompensators (except those products noted).

• Orion 93 and 97 ionplus Series sensing modules are warrantedto give six months of operation if placed in service before thedate indicated on the package, except 93-07 and 97-07 Nitratemodules are warranted to give ninety days of operation ifplaced in service before the date indicated on the package.

Six months from date of purchase by the user (or twelve months

57

from date of shipment from Thermo)

• Orion Flash Titration™ Probe (Orion 092518), pHuture™

Electrode (Orion 615700), pHuture MMS™ Pentrode™ (Orion617500), Quatrode™ (Orion 617800) and Triode™ (Orion615800), Low Maintenance Triode™ (Orion 9107BN), ORP LowMaintenance Triode™ (Orion 9179BN), and PerpHecT® LowMaintenance Triode™ (Orion 9207BN), Waterproof Triode™

(Orion 9107WP, 9107WL, 9109WL and 9109WP), QuiKcheK®

Meters and Micro Electrodes.

Three months from date of purchase by the user (or six monthsfrom date of shipment from Thermo)

• Economy Line Electrodes, Orion 91-05, 91-06, 91-15, 91-16,91-25, 91-26, 91-35, 91-36, 92-06. Warranty also includesfailure for any reason (excluding breakage), except abuse,provided the electrode is not used in solutions containing silver,sulfide, perchlorate, or hydrofluoric acid; or in solutions morethan one (1) Molar in strong acid or base at temperaturesabove 50 °C.

“Out-of-Box” Warranty - Should any of the following products failto work when first used, contact Thermo immediately forreplacement.

• Orion Solutions, Standards, Reagents, Cables, Ferrules, Tubing,Line adapters, Printers, Software, Cases, Stands, ProbeMembranes, AQUAfast® Test Strips, EZ Flash® columns, LiquidHandling Probes, Adapter Plates and Racks and generalaccessories.

For products in the catalog not listed in this warranty statement,please visit our website at: www.thermo.com.

THE WARRANTIES DESCRIBED ABOVE ARE EXCLUSIVE AND INLIEU OF ALL OTHER WARRANTIES WHETHER STATUTORY,EXPRESS OR IMPLIED INCLUDING, BUT NOT LIMITED TO, ANYIMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE AND ALL WARRANTIES ARISING FROMTHE COURSE OF DEALING OR USAGE OF TRADE. THE BUYER’SSOLE AND EXCLUSIVE REMEDY IS FOR REPAIR ORREPLACEMENT OF THE NON-CONFORMING PRODUCT OR PARTTHEREOF, OR REFUND OF THE PURCHASE PRICE, BUT IN NOEVENT SHALL THERMO (ITS CONTRACTORS AND SUPPLIERS OFANY TIER) BE LIABLE TO THE BUYER OR ANY PERSON FOR ANYSPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGESWHETHER THE CLAIMS ARE BASED IN CONTRACT, IN TORT

58

(INCLUDING NEGLIGENCE), OR OTHERWISE WITH RESPECT TOOR ARISING OUT OF THE PRODUCT FURNISHED HEREUNDER.

REPRESENTATION AND WARRANTIES MADE BY ANY PERSON,INCLUDING ITS AUTHORIZED DEALERS, REPRESENTATIVES ANDEMPLOYEES OF THERMO WHICH ALTER OR ARE IN ADDITION TOTHE TERMS OF THIS WARRANTY SHALL NOT BE BINDING UPONTHERMO UNLESS IN WRITING AND SIGNED BY ONE OF ITSOFFICERS.

59

ORDERING INFORMATION

Orion Description

9429BN Cupric Solid-State Epoxy Electrode, BNC Connector

942900 Cupric Solid-State Epoxy Electrode, U.S. Std. Connector

9429SC Cupric Solid-State Epoxy Electrode, Screw Cap Connector. Requires separate cable

9629BN ionplus® Series Cupric Solid-State Epoxy Electrode, BNC Connector

962900 ionplus Series Cupric Solid State Epoxy Electrode, U.S. Std. Connector

900200 Double-Junction Sure-Flow® Reference Electrode

900002 Double-Junction, Inner Chamber Filling Solution, 5 x 60 mL bottles

900003 Double-Junction, Outer Chamber Filling Solution, 5 x 60 mL bottles

900063 Optimum Results™ D Reference Filling Solution (for 96-29 Combination Cupric Electrode), 5 x 60 mL bottles

940011 ISA, 5 M NaNO3, 475 mL

948201 Polishing Strips, pk of twenty-four 6” strips

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SPECIFICATIONS

Concentration Range:10-8 to 0.1 M (6.4 x 10-4 to 6354 ppm)

pH Range:2 to 12 pH units

Temperature Range:0 °C to 80 °C continuous use80 °C to 100 °C intermittent use

Electrode Resistance:Less than 1 megohm

Reproducibility:± 4%

Size:Electrode Length: 110 mm (excluding cap)Diameter: For 94-29 12 mm

For 96-29 13 mmCap Diameter: 16 mmCable Length: 1 M

NOTE

61

NOTE

62

Environmental InstrumentsWater Analysis

North America 166 Cummings CenterBeverly, MA 01915 USATel: 978-232-6000Dom. Fax: 978-232-6015Int’l. Fax: 978-232-6031

Europe12-16 Sedgeway Business ParkWitchford, CambridgeshireEngland, CB6 2HYTel: 44-1353-666111Fax: 44-1353-666001

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Customer Support Toll Free: 800-225-1480 www.thermo.com Dom. e-mail: [email protected]’l. e-mail: [email protected]

For updated contact information, visit www.thermo.com

Analyze • Detect • Measure • Control™

227633-001 Rev. D

Orion Cupric Electrode - University of Utahring/Instrumental...separate reference electrode is unnecessary, making it convenient to use with small sample volumes. The free-flowing

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