بسم الله الرحمن الرحيم

الرحمن الله بسمالرحيم

Marine Analytical Chemistry

MC 361

(Chem 312)

Contents

• Introduction to Spectroscopy• Concept of Spectroscopy• Infrared Absorption• Ultraviolet Molecular Absorption Spectroscopy• Colorimetry (Spectrophotometry)• Emission Spectrography (Flame Photometery)• Total Organic Carbon (TOC)

Chapter 11-Introduction to Spectroscopy

• The Interaction between energy and matter:• In case of visible light

White light White light

Colorless solution

White light Blue + red

Purple solution

H2O K2MnO4

• In general

Radiant energy

Sample

Absoption

Interaction

Energy+MatterDetector

Wavelength range

-ray x-ray visible IRUV radio micro

Increase in energy

Decrease in wavelength

Decrease in frequancy

What is Radiant Energy?

• Wave?? Or Small Particles??

• Properties: Wave like character

• λ = wavelength γ = frequency

• Energy E = hγ

• h=Planck constant (6.6256 x 10-27 erg/sec)

• γ= C/λ C= speed of light

• E = h C/λ

What is Matter?

Matter: Atoms or Molecules

Gases (alone)

Liquid (agglomerates)

Solid (crystal or random)

Motion of Molecules

Rotational

Vibrational

Translational

• Both chemical structures and the arrangement of the molecules affect the way in which any given material interacts with energy.

How does radiant energy interact with matter?

• A given molecule can absorb only radiation of a certain definite frequency.

• Red, blue and yellow light not just a single wavelength or frequency.

• Given molecule can exist only in certain well-defined energy state.

BlueWhite light

Blue glass absorbered and yellow

Blackred or yellow

Blue glass absorbered and yellow

Molecule or atom in ground energy state

Molecule or atom in higher energy state

E = h

• Energy levels are not continuous.• Quantized? The energy difference

between two defined energy levels is fixed.

• The molecules or atoms of same chemical species absorb same frequency.

• The molecules or atoms of different chemical species absorb different frequency

• The uniqueness of the frequencies at which a given molecular species absorbs is the basis of absorption spectroscopy.

The Absorption of Energy by Atoms

The Franck-Hertz Experiment

Electron gunCollision chamber

HgDetector

E1

E0

E2

E3

E=4.9 ev (6-1.1)Excited Hg

Collision of Bodies

Elastic collisionNo exchange of energy between bodies

Inelastic collisionExchange of energy between bodies

The Absorption of Energy by Molecules

E0

E1

Absorb radiant energy

TransitionBasis of

Absorption spectroscopyIR, AA,UV, X-ray

E0

E1

Emission of radiant energy

EmissionBasis of

Emission spectroscopy

Emission spectroscopyMolecular flurescenceFlame photometer

Molecular Motion

Rotation Vibration Transition

MoleculeRotates

RotationalEnergy

MagneticMoment

RotationalEnergyStates

TransitionE= (very small) Radio,Micro

Unexploited due to experimental difficulties

Vibration of Molecules

VibraionalEnergy

bond MagneticMoment

VibrationalEnergyStates

TransitionE = IRVibrational

+Rotational

IR spectroscopy shape and structure of molecules (function groups)

Absorption Caused by Electronic Transistors in Molecules

Molecular orbitals Ground state

Excited state

UV and Vis.electron E =(very narrow frequancy band)

• The vibrational and rotational energies of the molecules are added to the electronic energies.

• The difference in vibrational or rotational energy leads to the absorption of energy over wide frequency range.

The Effect of the Absorption of Energy

Electromagnetic spectrum Long wavelength IRRotational and Vibrational

Functional groupsOrganic molecules

Nondestructive.UV and Visible

Electronic excitationUnsaturated organic

Aromatic ,olefins, X,NNondestructive.

X-rayRemove e from inner shelle of outer shell fill up inner

shell ------ X-rayDimensions of crystals

Elemental analysis.Very short wavelength

Penetrate the nucleiof atom.

Change to different element Basis of nuclear science.

The Emission of Radiant Energy by Atoms and Molecules

Atom (AO)

Radiant Energy

Ground state

Exited states

10-6 sec

hEmite photon

Energy

Ground state

Exited states

+

Each atom

own energy levels

different hdifferent emission lines

emission spectrum of the elementEmission spectroscopy

In the case of molecules

• Not all molecules fluorescence, and very few phosphorescence.

• Fluorescence intensity is very high.• Can detect very small conc. of certain compound

Molecules (MO)

Ground state

Exited states

10-6 sec

hEmite photon

Energy

Ground state

Exited states

+

(fluorescence)

(phosphorescence)

Methods of Excitation of Atoms

• 1-Electronic Discharge• Putting the sample in an

electric discharge between two electrodes.

• The sample breaks down into excited atoms

• All different atoms emit their emission spectrum.

ElectrodesElectrical discharge

Sample

2-Flame Excitation

Molecule

Flame

Thermal energy

Breaks downAtoms

ExcitedEmite Chracteristic spectra

• This is the basis of flame photometry.• Flame energy is lower than that of an electrical

discharge• Fewer transitions are possible-Fewer spectrum

lines.

3-Excitation by Radiation• Sample absorb uv and

reemit fluorescence.• This the bases of Molecular

Fluorescence (RF).

• Phosphorescence:• If the e changes its direction

of spin before returning to the G.S. emission will be difficult (forbidden).

• The radiation takes place over a long period of time.

Sample

Detector

UV Unabsorbed radiation

Fluorescent radiationfrom sample

Absorption LawsI0 I1

I0 : intensity of a beam of radiation that falls on solution

I1 : intensity of a beam of radiation emerging from solution

T : Trancmittance - Fraction of light transmitted by solution

TI1

I0=

I0 = 100 I1= 50 I2=25

50%absorbed

50%absorbed

logarithmic relationship

A1

T= log10

I0

I1

T= log10-

A = log10I1

I0

= log10-

A : absorbance

1-Lambert׳s Law

• A = a b• A = absorbance• a = absorptivity of the liquid• b = optical path length

• a b = log I0/I1

• I1 = I0 10 -ab

• I0 = I1 10 ab

• Relationship between absorbance and optical path length

2- Beer΄s Law

• A = a c• c = concentration of

solution.• a c = log I0/I1

• I1 = I0 10 -ac

• I0 = I1 10 ac

• Relationship between the absorbance and the concentration of the solution

I0= 100 I1= 50

b

0.1g/100ml

I0= 100 I1= 25

b

0.2g/100ml

3-Beer-Lambert Law

• A = a b c • I0 = I1 10 abc

• Linear relationship between A and c if b is constant and the radiation wavelength constant.

• By measuring I1/I0 we can measure A, and we can calculate c.

• Valid for low conc. But deviations are common at higher concentrations.

4-Deviation from Beer׳s Law

• 1-Impurities.• 2-Chemical equilibrium.• 3-Optical slit.• 4-Dimerization.• 5- Interaction with solvent• Calibration curve will

eliminate all the deviations.

Abs

orba

nce

Concentration0 1

1

2 3 4

Calibration Curves• Series of solutions with

known concentration.

• When a, b, I0 are constant

• c ά –logI1

• Base line disturbed by an interfering compounds.

• Can solve this problem :• 1-Mathmatically• 2-Double beam

instrument (reference cell)

Ab

sorb

an

ce

Concentration0 2

1.0

4 6 8

0.25

0.5

0.75

2-Standard Addition Method• This method used if:• 1-No suitable calibration

curve.• 2-Time delay.• 3-No sufficient information

on the solvent in the sample.

• 4-Very low concentration.• Known conc. are added to

the sampleA

bso

rba

nce

Concentration0 2

1.0

4 6 8

0.25

0.5

0.75

Chapter 2Concepts of Spectroscopy

Spectroscopy

Emission AbsorptionIt is important to know1- The wavelength at which the sample emits or absorbs radiation.2- The intensity of radiation or the degree of absorption.

The basic design of all instruments:1- Source of radiation (absorption) or excitation (emission).2- Monochromatic (selecting the wavelength).3- Sample holder.4- Detector (measure the intensity of radiation).

Spectroscopy instruments

Single-Beam Optics Double beam Optics

• 1- single beam optics:

a- Radiation Source• 1-Emite radiation of wavelength in the

range to be studied (x-ray, infrared, ultraviolet).

• 2-The Intensity in all range should be high.

• 3-The intensity should not vary significantly at different wavelengths.

• 4-The intensity should not fluctuate over long time intervals.

b-Monochromator• Function: disperse the

radiation according to the wavelength.

• 1-Prism Monochromators:• The prism bends longer-

wavelengths (red end) radiation less than it does shorter-wavelength radiation (blue end)?.

• The refractive index of prism is greater for short-wavelength light than it is for long-wavelength light.

2-Grating Monochromator: • More popular than prism.• A series of parallel lines cut

into a plane surface.• From 15000-30000 groves per

square inch.• The more lines per square

inch, the shorter λ of radiation that the grating can disperse and the greater the dispersing power.

• Separation of light occurs because light of different λ is dispersed at different angles.

3-Resolution of a Monochromator• The ability to disperse radiation is called

resolving power (dispersive power).

• The resolving power of a prism increase with the thickness of the prism.

• The resolving power of a prism increase when the material used is improved.

• The resolving power of a grating increase with increase the line groves.

c-Slits• Used to select the light beam after it

has been dispersed by the monochromator.

• The entrance slit selects a beam of light from the source.

• The exit slit allow radiation from the monochromator to proceed to the sample and detector.

• Only a selected λ range is permitted through the slit.

• Other radiation is blocked and prevented from passing further.

• The slits are kept as narrow as possible to ensure optimum resolution.

d-Detector• Measure the intensity of the radiation that

falls on it.• Radiation energy is turned into electrical

energy.• The amount of energy produced usually

low and must be amplified.• Amplifying the signal from the detector

increase its sensitivity.• If the signal is amplified too much, it

becomes erratic and unsteady (noisy).

e- Uses for Single-Beam Optics• Single-beam optics are used for all

spectroscopic emission methods.• The method allows the emission intensity and

wavelength to be measured accurately and rapidly.

• In spectroscopic absorption studies the intensity before and after passing the sample must be measured.

• Any variation in the intensity lead to analytical error. (that is why double beam developed)

2-The Double-Beam System.• Used for spectroscopic

absorption studies.• One very important

difference from single beam:

• The radiation from the source is split into two beams with equal intensity (reference beam and sample beam).

• Any variation in the intensity of source I0 simultaneously decreases I1 but does not change the ratio I1/I0.

Chapter 3Infrared Absorption.

• The wavelength (λ) of infrared (ir) radiation falls in the range 750 nm- 4500 nm.

• The frequency () range:

2.2x1014-7.5x1015 cps.

• Infrared radiation has less energy than visible radiation but more than radio waves.

A-Requirements for Infrared Absorption

• 1-Correct Wavelength of Radiation:• Molecules absorb radiation when some part of

the molecule (atom, or group) vibrates at the same frequency as the incident radiant energy.

• After absorbing radiation, the molecule vibrate at an increased rate.

• Atoms can vibrate in several ways.• The rate of vibration is quantized and can take

place only at well defined frequencies that are characteristic of the atom.

C

H

O

H

2-Electric Dipole• For a molecule to be able to

absorb ir, it must have a changeable electric dipole.

• The dipole must change as a result of the vibrational transition resulting from ir absorption.

• If the rate of change of the dipole during vibration is fast, the absorption of radiation is intense (and vice versa).

C

H

O

H

Electric dipole: a slight positive and a slight negative electric charge on the atoms

B-Movements of Molecules:

• The total radiant energy absorbed by molecules = (the molecule's vibrational energy + the molecule's rotational energy)

• Rotational energy levels are very small compared to vibrational energy levels.

1- Vibrational Movement

C

H

H

H

H

Vibrating spring

M1 M2

= Kf

M1

M1

M2

M2 =

+

: frequency of vibration• K : constant.• f : binding strength of the spring : reduced mass.

• Modes of vibration of C and H in methane molecule including:

• a-symmetrical stretching.• b- asymmetrical stretching.• c- scissoring.• d- rocking.• e- wagging.• f- twisting.

• Each of the modes vibration absorb radiation at different wavelength.

C

H

H

a-symmetricalstreching

b-asymmetricalstreching

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

c-scisoring d-rocking

e-wagging f-twisting

2- Rotational Movement• At the same time that the parts of a

molecule vibrate toward each other, the molecule as a whole may rotate (spin).

• The energy involved in spinning a molecule is very small compared to the energy required to cause it to vibrate.

C-Equipment (double beam system)• 1- Radiation Source:

a-Nernest Glowers

b-Globars

(zirconium oxide, cerium oxide, thorium oxide)

(silicone carbide)

heated electrically

1000-1800 CIR

Both sources fulfill important requirements:1-steady intensity. 2-intensity constant over long periods of time.3-wide wavelength range.But the intensity of the radiation from them is not the same at all frequencies.

2- Monochromators• Select desired frequency from source, and

eliminate the radiation at other frequencies.• a- Prism Monochromator: • Material must be:• 1- Transparent to IR radiation (not glass, not

quartz).• 2-Smooth (prevent random scattering).• 3-High quality crystal.• 4-Dry all time (use heater to keep dry).• 5-The machine must be in air condition room.• Material used can be single large crystal metal

salt : NaCl, (KBr,CsBr), or CaF2.

B-Grating Monochromators:• Recently it is more popular in IR

spectroscopy.

• Material : Aluminum.

• Advantages of grating:

• 1- Stable in the atmosphere and are not attacked by moisture.

• 2- Can be used over considerable wavelength range.

3- Slit Systems:• Allow small section of radiation beam to

pass through exit slit to the detector.

• 4- Detectors:a-Bolometers

Thin metal conductor irwarm electrical resistance

change

Degree of change = amount of radiation

b-Thermocouples:Metal A

Metal B

weilded junctionweilded junctionHot Cold

kept at constant tempratureExposed to the ir radiation

Potential differance genrateddependes on temperature differance

between the junctions

• C- Thermistors:• Made of fused mixture of metal oxide.• As their temperature increase, their resistance

decrease (as bolometers).

5- sample Cell:• IR spectrum can be used for the characterization

of solid, liquid, or gas samples.• The material used to contain the sample must

always be transparent to ir radiation.

• a- solid samples:

• Mixing ground solid sample with powdered KBr.• Press the mixture under very high pressure

(small disk 1cm diameter and 1-2 mm thickness)• (called KBr pellet method).

b-Cells for Liquid Samples• The easiest samples to handle are liquid

samples.• Cells made of rectangular of NaCl, or KBr.• All cells must be protected from water

because they are water soluble.• Organic liquid samples should be dried.

• c-Gas samples:• The gas sample cell is similar to liquid

samples (NaCl, or KBr), but longer than liquid samples (about 10 cm long).

D- Analytical Applications:• 1- Qualitative Analysis:• Function groups in organic compounds

(methyl, aldehyde, ketone, alcohol, atc.).• Information about the geometry of

molecule.• 2-Quantitive Analysis:• By using a solution with known

concentration, we could measure the concentration of unknown sample using Beer's law.

3- Analysis Carried Out by IR Spectroscopy:• 1-Detection of paraffins, aromatic, olefins,

acetylenes, alcohols, ketones, carboxylic acids, phenols, esters, ethers, amines, sulfur compounds, and haldies.

• 2-Distinguish one polymer from another.

• 3-Identify atmospheric pollutants.

• 4-Examine the old painting and artifacts.

• 5-Determine the make and year of the car.

• 6-Determine the impurities in raw material.

Absorption IR Spectrum

Methyl Ethanoate ir spectrum

Chapter 4Ultraviolet Molecular Absorption Spectroscopy

• Wavelength range : 200 – 400 nm.• Visible light act in the same way as uv light

(consider as a part of the uv range).

200 - 400 nm

Function Analytical field Analytical Application

Atomic uv

Absorption of uv Atomic Absorption Quantitative analysis

Emission of uv Flame photometry Quantitative analysis: Alkali metals, alkaline metal earths

Molecular uv

Absorption of uv uv absorption Qualitative and quantitative for aromatics

Emission of uv Molecular fluorescence

Detection of small quantities of aromatics

Emission of uv Molecular phosphorescence

Limited application

1-Electronic Excitation

G.S. G.S.

Ex.S.

Electronic

excitation

E = h= (E1 - E0)(uv range)

E1

E0

• Three types of electrons are involved in organic molecules

Saturated Unsaturated Non-bonding

Symbol n

Example Paraffinic compounds

(C-H)

Conjugated double bond

(Aromatics)

Organic compounds

contain O, S, Cl.

Absorbance of uv Can‘t absorb uv (need higher

energy)

Absorb uv Absorb uv

2-The Shape of UV Absorption Curves.

Electronic transition

Molecular vibration

Molecular rotation

Time 10-15 sec (fsec.)

10-12 sec 10-10 sec

Energy UV

High energy>

IRLow energy>

MicroVery low energy

• The electronic excitation line is split into many sublevels by vibrational energy.

• Each sublevel is split by rotational energy.• The gross effect is to produce an absorption

band rather than an absorption line.

UV Spectrum of DNA

1- General Optical System• a- Single beam system:• Single beam problems:• 1-Measure the total light absorbed, rather

than the percentage absorbed. • 2-Light may be lost by reflecting surfaces.• 3-Light may be absorbed by solvent used.• 4-The source intensity may vary with

changes in line voltage.• 5-The sensitivity of the detector varies

significantly with the wavelength.

B- Double-beam System:• All the previous problems can be largely

overcome by using the double-beam system.

• The source radiation is split into two beams of equal intensity.

• One beam to the reference cell and the other to the sample cell.

• The difference in intensity of the two beams should be a direct measure of the absorption of sample.

2- Components of the Equipment:• a- Radiation source:• 1- Tungsten lamp: heated electrically to

white heat, stable, common, easy to use, but the intensity at short wavelengths is small.

• 2- Hydrogen lamp: hydrogen gas in high pressure with electrical discharge.H2 molecules excited and emit uv radiation.

• 3- Deuterium lamp: D2 is used instead H2. Emission intensity is increased three times.

• 4- Mercury discharge lamp: Hg vapor in the discharge lamp is under high pressure.

• 5- Xenon lamp: Like H2 lamps. They provide very high radiation intensity.

• B- Monochromators:• Prism and grating are used in uv spectroscopy.• 1- Glass: has the highest resolving power, but it

is not transparent to radiation between 350-200 nm.

• 2-Fused silica: more transparent to short wavelengths, but very expensive.

• 3-Quartz: used extensively in uv spectrophotometers.

C- Detectors:• 1- Photocell:• Consists of a metal

surface (cathode) that is sensitive to light.

• When light falls upon it, the surface gives off electrons, which attracted and collected by an anode.

• Current created measure the intensity of light.

2-Photomultiplier:• Work in a similar way like

photocell.• Electrons attracted to +ve

dynode, that cause several electrons to emit.

• This process repeated several times until a shower of electrons arrive at a collector.

• A single photon may generate many electrons and give a high signal.

3- Sample cell:• The cells used in uv absorption must be:

• a- Transparent to uv radiation.

• b- Chemically inert.

• Quartz or fused silica are most common material used.

C-Analytical Applications• 1- Qualitative analysis:

• Nonbonding electrons and electrons absorbed over similar wavelength range.

• This makes it difficult to identify the presence of any particular group (function groups).

• UV is very useful in detecting aromatic compounds and conjugated olefins.

2- Quantitative Analysis:

• Powerful tool for quantitative determination of compounds that absorb uv (nonbonding electrons and conjugated bond compounds).

• Using Beer's law and calibration curve can calculate the concentration of unknown sample that absorb uv.

• The technique is quite sensitive as low as 1 ppm.

3- Applications:• Determination of:• 1-Polynuclear compounds.• 2-Natural products.• 3-Dye-stuff.• 4-Vitamines.• 5-Impuirties in organic samples.• In the field of agriculture can determine:• 1-Pesticides on plants.• 2-Polluted rivers, and in fish and animals.

• In the medical field can be used for the analysis of:

• 1-Enzymes, vitamins, hormones, steroids, alkaloids, and barbiturates.

• 2-Diagnosis of diabetes, kidney damage.

• In pharmacy: purity of drugs.

• Measure the kinetics of chemical reactions

• In HPLC as detector.

Chapter 5Spectrophotometry

• Measure how much light is absorbed by sample solution (light intensity).

• There are single-beam and double-beam spectrometers.

• Electronic transition (excitation) of electrons in the last orbital (absorb light in the visible range 400-850 nm).

A-Spectrophotometeric equipment • 1- Source:

• Tungsten lamp: heated electrically to white heat (400 – 850 nm).

• The signal must be constant over a long periods of time.

• The signal intensity is not exactly equal at different wavelengths (double beam system solve this problem).

• 2-Monochromator:

• a- Light filter:

• Allows light of the required wavelength to pass, but absorbs light of other wavelengths.

• Several filters can be used for different analysis.

• b- Glass prism:

• Easier than filters as any required wavelength may be chosen.

• 3- sample cell:• For visible part of the spectrum cells are from

glass.• Quartz cells used if the studies involving both uv

and visible regions.• 4- Detectors:• Most common are photomultipliers or photocell.• Convert the radiant energy to electrical energy.

• Double-beam instrumentation gives more accurate absorption spectra and more accurate quantitative measurements.

2- Analytical applications:• Spectrophotometry is very widely used

method of quantitative analysis.

• Whenever the sample is color we can use spectrophotometry.

• If the sample is colorless we can color it using special reagent (ex. NO2

-, PO4-3,..).

• This technique is sensitive and accurate but time consuming.

• Requirements for this process:

• 1- Selective reagent react only with a specific ion.

• 2- Must undergo color change.

• 3- Intensity of the color should be related to the concentration of the ions in the sample.

Chapter 6Emission Spectrography

• Emission spectrography: is the study of the radiation emitted by a sample when it is introduced into an electrical discharge.

• Since each element emits a different spectrum, it is possible to determine what element are present in the sample.

• Most important technique for elemental qualitative analysis for: all metallic elements, metalloids (liq. or solid), halides, and inert gases.

• Quantitative analysis: concentration levels as low as 1 ppm.

A-Origin of SpectraExcited state

Electrical

dischargeG.S. G.S.Lower energy orbital

Higher energy orbital

Emitphoton

Bases Emissionspectrography

• Using thermal energy: Flame photometry.• Using spectral energy: Atomic fluorescence.• Electrical discharge: Produces more energy and

therefore causes brighter spectra than the other forms.

B-Equipment:

Slits

• The sample introduced to electrical discharge, where it is excited.

• Excited sample emits radiation, which is detected and measured by the detector.

1- Electrical sourceDC arc (spark) AC arc (spark)

Voltage 50-300 v 10-50 v (low)

Intensity High temperature intense radiation

Low intensity than DC but more reproducible.

Application Qualitative analysis of trace

components when high sensitivity is

required

Useful for quantitative

analysis.

2-Sample Holder• a- Solid Sample:• Solid sample reducing to powder, then

loading the powder to carbon sample holder which act as one electrode used in the discharge.

• Animal tissue and plant materials change to ash then mix with carbon or alumina to avoid sudden emission.

• Metallic samples (alloys or pure metals) can use as it is after clean and shape it to be one electrode.

• b- Liquid samples:

• Liquid samples may be analyzed directly by the following method:

• 1-Cup container.

• 2-Rotating disk.

• Both methods gives steady rate into the electrical discharge.

• Organic solutions tend to ignite in the discharge and cause erratic emission.

3-Monochromator:• The function of the monochromator is to

separate the various lines of a sample's emission spectrum.

• a-Prism monochromators:• Quartz or fused silica suitable for

transparent to uv radiation.• Polarization: the act of separating a light

beam into two beams vibrating at right angles to each other.

• Quartz prisms split light into two beams of light that are polarized perpendicularly to each other.

• Beam splitting causes the loss of half the lights intensity, making both qualitative and quantitative analysis difficult.

• This problem can overcome by using two half prisms. The first splits the light into two beams; the second recombines them.

b- Grating monochromators:

• It gives better resolution than prisms.

• Concave gratings can be used to conserve energy.

• A given wavelength that falls on the concave grating to focus at a given point.

• This relationship helps us to locate the correct position for placing either photographic film detector or a series of photomultipliers.

4-Slits:• Two parallel metal strips.• Slits might be 1 cm high and 0.1 mm wide,

the width can be varied for resolution requirements.

• Entrance slits: keep out stray light and permit only the light from the sample to enter the optical path.

• Exit slits: placed after the monochromator block out all but the desired wavelength range from reaching the detector.

5- Detectors:• a- Photographic plates: or films used for all qualitative

analysis.• For quantitative analysis the intensity of one emission

line from each element is measured, which correlated with the concentration of the related element in the sample.

• b- The photomultiplier:

• The photomultiplier is used only for quantitative work.

• The immediate response and ease of interpretation make it the most desirable detector.

C-Analytical Applications• Emission spectrograph used for elemental

qualitative and quantitative analysis. But gives very little direct information on the molecular form.

• The sample is destroyed by the electrical discharge.

1-Qualitative Analysis• a-Raies Ultima:

• When the metal excited, it emits complex spectrum that consists of many lines, some strong, some weak.

• By dilution of the sample, the weaker lines disappear. Further dilution less strong lines disappear until only a few are visible.

• The lines that are left called raies ultima or RU lines (three lines should be detected).

b- Metals• Most elements can be detected at low

concentrations with a high degree of confidence?? Because the emission spectra for most elements in the periodic table are intense, moreover the background interference is greatly reduced.

• Unknown sample is taken together with the spectrum of iron. By comparison with the iron spectra, the elements in the sample can be identified.

2-Quantitative analysis:• It carried out by measuring the intensity of one

emission line of the spectrum of each element to be determined.

• The choice of the line depend on the concentration of the element.

• For small concentrations of the element, an intense line must be used. With a larger concentration, a weaker line would be measured.

• New machines contain more than photomultiplier detectors can measure up to 60 element simultaneously.

• Calibration curves must be prepared for each element to be determined.

Specific Applications• Metallurgy: the presence of iron and steel of

many elements like Ni, Cr, Si, Mg, Mo, Cu, Al, As, Sn, Co, V, Pb, and P can be determined by emission spectrography.

• Alloys: the percentage of different metals can determined by emission spectrography.

• Oil industry: the amount of different metals in the oil which the degree of purity of oil.

• Soil samples, animal tissue samples, and plant roots have been analyzed for many elements.

Chapter 7Examples of Absorption and

Emission Instruments.• A-Emission Instruments:

• 1-Flame photometry (atoms):• Flame photometry is an atomic emission method for the

routine detection of metal salts, principally Na, K, Li, Ca, and Ba.

• The low temperature of the natural gas and air flame, compared to other excitation methods such as arcs, sparks, and rare gas plasmas, limit the method to easily ionized metals.

• Since the temperature isn't high enough to excite transition metals, the method is selective toward detection of alkali and alkali earth metals.

• Quantitative analysis of these species is performed by measuring the flame emission of solutions containing the metal salts.

• Solutions are aspirated into the flame.

• The hot flame evaporates the solvent, atomizes the metal, and excites a valence electron to an upper state.

• Light is emitted at characteristic wavelengths for each metal as the electron returns to the ground state.

• Optical filters are used to select the emission wavelength monitored for the analyte species.

• Comparison of emission intensities of unknowns to the standard solutions, allows quantitative analysis of the analyte metal in the sample solution.

• Advantages:

• Flame photometry is a simple, relatively inexpensive method used for clinical, biological, and environmental analysis.

• Disadvantages:• The low temperatures of this method lead to

certain disadvantages:• 1- Most of them related to interference and the

stability of the flame and aspiration conditions.• 2- Fuel and oxidant flow rates and purity of fuel.• 3- Aspiration rates, solution viscosity of samples.• It is therefore very important to measure the

emission of the standard and unknown solutions under conditions that are as nearly identical as possible.

• 2- Spectrofluorimetry (Molecules):

• Measurement of fluorescence - a form of light emitted by a substance after irradiation at other wavelengths.

• Origin of Photoluminescence

• Absorption of visible or UV radiation raises molecule to an excited state.

• Electron absorbs quantum of energy and jumps to a higher energy orbital.

• When electron drops back to the ground state, excitation energy can be liberated by:

• 1- QUENCHING (or RADIATIONLESS TRANSFER)- Most commonEnergy temporarily increases vibrational and rotational energy of bonds in the molecule - ultimately dissipated as heat in surrounding solvent.

• 2- RE-EMISSION OF RADIATION,- Less commonGives rise to... FLUORESCENCE and/or PHOSPHORESCENCE(two forms of PHOTOLUMINESCENCE)

• Stokes' Law Of Fluorescence:

• ENERGY JUMP UP(from ground to excited electronic state) is larger than ENERGY JUMP DOWN(for the reverse transition).

• The wavelength of light absorbed for excitation will be shorter than the wavelength emitted during de-excitation. (Stokes' law)

Fluorescence vs Phosphorescence

• FLUORESCENCE: if it occurs, is within nanoseconds (10-9 sec) of the excitation.

• PHOSPHORESCENCE : is caused by electron becoming transferred into a triplet state. (Electrons of the same spin in the one orbital). It is much slower (vary from milliseconds to weeks) (and rarer) process.

Instrumentation : The Spectrofluorimeter

A Fluorescent Species Has Three Spectra

• Not every absorption peak gives rise to fluorescence.

• However peaks in a fluorescence excitation spectrum usually correspond closely in wavelength to absorption peaks.

• Fluorescence emission spectrum has maximum at higher wavelength than excitation spectrum (Stokes' law).

• Emission spectrum is usually simpler - usually only a single broad peak.

• Fluorescence is not measured relative to a blank.

• Quantitative Spectrofluorimetry

• Linear response, Fluorescence vs Mass of Analyte, only at LOW CONCENTRATIONS.

• Advantages and Disadvantages of Spectrofluorimetric Assay

• Major advantage is high sensitivity.(better than spectrophotometer).

• A potential advantage is improved selectivity.

• Requirement to set two wavelengths in spectrofluorimetry (excitation and emission) hence unlikely that an impurity is being co-measured - it would have to absorb and emit at the same two wavelengths.

• Disadvantages :a very exacting technique, requiring careful attention to experimental detail, including purity of reagents.

• What Compounds Fluoresce?

• 1- Most fluorescent species are compounds that absorb UV light.

• 2- An aromatic ring is the most common structural requirement.

• 3-Additional requirement for fluorescence is that quenching must not occur while the molecule is in the excited state.

• 4- In aromatic molecules, electron withdrawing groups tend to produce quenching. eg -NO2, or -COOH substituents on the aromatic ring tend to decrease the chances of fluorescence.

• 5- Electron rich groups inhibit quenching. eg -NH2 or -OH are likely to enhance the fluorescence.

• Product has 4 electron donor groups. Highly fluorescent at 530 nm (360 nm excitation).

B- Absorption InstrumentsTotal Organic Carbon (TOC)

• There are two types of TOC measurement methods, one is the differential method (TC-IC = OC) and the other is the direct method (NPOC).

• In differential method both TC (Total Carbon) and IC (Inorganic Carbon) determined separately .

• This method is suitable for samples in which IC is less than TOC, or at least of similar size.

• In the direct method : first IC is removed from a sample by purging the acidified sample with a purified gas, and then TOC may be determined by means of TC (TC = TOC).

• This method is also called as NPOC .

• The direct method is suitable for surface water, ground water and drinking water (negligible amount of POC in these samples).

Scheme for TOC machine.

TC measurement:• TC is measured by injecting of tens micro

liter, of the sample into a heated combustion tube packed with an oxidation catalyst. The water is vaporized and TC, is converted to carbon dioxide (CO2).

• The carbon dioxide is carried with the carrier gas stream from the combustion tube to a NDIR ( non-dispersive infrared gas analyzer) and concentration of carbon dioxide is measured.

IC measurement:• IC is measured by injecting a portion of the sample into an

IC reaction chamber filled with phosphoric acid solution.

• All IC is converted to carbon dioxide and concentration of carbon dioxide is measured with a NDIR.

• TOC may be obtained as the difference of TC and IC.

Organic MatterCnHm

Heat

Cat.O2CO2H2O (gas)

Condenced H2O

Cool To

NDIR

+

• In the direct method the sample from which IC was removed previously, injected into the combustion tube and TOC (NPOC) is measured directly.

Organic Matter H+

TC = TOC + ICIC change to CO2

Purge+ (TC = TOC)

O2

CO2H2O (gas)

Cool To

NDIR

+

Condenced H2O

Total Nitrogen Analyzer• Total nitrogen analyzer based on catalytic

thermal decomposition. Chemiluminescence method.

• First, nitrogen (N) compound is oxidized at high temperature (600 to 900°C) by the catalytic thermal decomposition method to generate nitrogen monoxide (NO).

CatalystN.compound NO

O2Heat

• Next, this nitrogen monoxide (NO) is reacted with ozone (O*) to form NO2*.

• Nitrogen dioxide (NO2*) excited in metastable state then generates chemiluminescence when it becomes stable nitrogen dioxide (NO2).

• Intensity of this chemiluminescence is proportional to the nitrogen concentration.

NO + O* NO2* NO2+ h

TOC solid module • IC (solid) subjected to:

• 1 ml H3PO4 then introduce to oven at 200 C only.

• For detection of TOC in solid samples.• TOC measurement method is the differential method (TC-IC = OC).• Both TC (Total Carbon) and IC (Inorganic Carbon) determined separately.•TC (solid) introduce directly to oven at 700 C