Instrumental methods of analysis. Instrumental methods of analysis. Photometry.Photometry.

Lecture 12Lecture 12

Associate prof . L.V. VronskaAssociate prof . L.V. VronskaAssociate prof . M.M. MykhalkivAssociate prof . M.M. Mykhalkiv

OutlineOutline1.1. Classification, advantages and lacks of physical-Classification, advantages and lacks of physical-

chemical methods of the analysis.chemical methods of the analysis.

2.2. Optical methods of the analysis. Classification.Optical methods of the analysis. Classification.

3.3. The fundamental law of absorption.The fundamental law of absorption.

4.4. Electronic spectrum.Electronic spectrum.

5.5. Photometric method of analysis: an essence, Photometric method of analysis: an essence, theoretical bases, usage in the pharmaceutical analysis.theoretical bases, usage in the pharmaceutical analysis.

6.6. Multiwave spectrophotometryMultiwave spectrophotometry ..

7.7. Differential spectrophotometry.Differential spectrophotometry.

8.8. The extraction-photometric analysis.The extraction-photometric analysis.

9.9. Photometric titration.Photometric titration.

1. Classification, advantages and lacks 1. Classification, advantages and lacks of physical-chemical methods (PCMA) of physical-chemical methods (PCMA)

of the analysis.of the analysis.

Physical and physical-chemical methods Physical and physical-chemical methods of the analysisof the analysis are based on dependence are based on dependence application between measured physical application between measured physical properties of substances and qualitative properties of substances and qualitative (quantitative) composition(quantitative) composition

PCMAPCMA are dividedare divided onon:: OpticalOptical methods are based on measurement of optical methods are based on measurement of optical

properties of substances.properties of substances. ChromatographicChromatographic methods are based on usage of ability of methods are based on usage of ability of

different substances to selective sorption.different substances to selective sorption. ElectrochemicalElectrochemical methods are based on measurement of methods are based on measurement of

electrochemical properties of substances.electrochemical properties of substances. RadiometricRadiometric methods are based on measurement of methods are based on measurement of

radioactive properties of substances.radioactive properties of substances. ThermalThermal methods are based on measurement of heat effectsmethods are based on measurement of heat effects

of substances.of substances. Mass spectrometricMass spectrometric methods are based on studying of the methods are based on studying of the

ionized fragments ("splinters") of substances.ionized fragments ("splinters") of substances. KineticKinetic methods are based on measurement of dependence methods are based on measurement of dependence

of speed of reaction from concentration of substanceof speed of reaction from concentration of substance

Advantage of PCMAAdvantage of PCMA High sensitivityHigh sensitivity - a low limit of detection (10 - a low limit of detection (10-9-9

g) and definitiong) and definition High selectivityHigh selectivity Rapid analysisRapid analysis methods methods Automation and computerization Automation and computerization is possibilityis possibility Analysis is Analysis is possibility on distancepossibility on distance Possibility of the Possibility of the analysis without destruction of analysis without destruction of

the samplethe sample Possibility of the Possibility of the local analysislocal analysis

Lacks of PCMALacks of PCMA Definition error is near Definition error is near ± ± 5 %5 % (on occasion to (on occasion to 20 20

%%), whereas - ), whereas - 0,01-0,005 % for gravimetry and 0,01-0,005 % for gravimetry and 0,1-0,05 % for titrimetry0,1-0,05 % for titrimetry

Reproducibility of resultsReproducibility of results in separate methods is in separate methods is worse, than in classical methods of the analysisworse, than in classical methods of the analysis

It is necessary of usage It is necessary of usage of standards and of standards and standard solutions, graduation of equipment standard solutions, graduation of equipment and plotting of calibration chartsand plotting of calibration charts

Complexity of used equipment, its high cost, Complexity of used equipment, its high cost, high cost of standard substanceshigh cost of standard substances

2. Optical methods of the analysis. 2. Optical methods of the analysis. Classification.Classification.

А) On investigated objectsА) On investigated objects The nuclear spectral analysisThe nuclear spectral analysis The molecular spectral analysisThe molecular spectral analysis

B) On the nature of interaction of electromagnetic B) On the nature of interaction of electromagnetic radiation with substanceradiation with substance

1.1. Absorption analysisAbsorption analysis Atomic-absorption analysisAtomic-absorption analysis Molecular-absorption analysisMolecular-absorption analysis Turbidimetric analysisTurbidimetric analysis

2. The emissive spectral analysis2. The emissive spectral analysis flame photometryflame photometry fluorescence analysisfluorescence analysis The spectral analysis with usage of effect of The spectral analysis with usage of effect of

combinational dispersion of lightcombinational dispersion of light

3. Other methods3. Other methods nephelometric methodnephelometric method refractometric analysis refractometric analysis polarimetric analysispolarimetric analysis interferometric analysisinterferometric analysis

C) On electromagnetic spectral range which use C) On electromagnetic spectral range which use in analysis:in analysis:

Spectroscopy (spectrophotometry) in UV and Spectroscopy (spectrophotometry) in UV and visible spectrumvisible spectrum

IR - SpectroscopyIR - Spectroscopy X-ray spectroscopyX-ray spectroscopy Microwave spectroscopyMicrowave spectroscopy

D) By the nature of energy jumpD) By the nature of energy jump Electronic spectrumElectronic spectrum Vibrational spectrumVibrational spectrum Rotational spectrumRotational spectrum

Spectrum (method)Spectrum (method) The characteristic of The characteristic of energy of energy of quantumquantum

Process Process

Radio-frequency Radio-frequency (NMR, EPR)(NMR, EPR)

MicrowaveMicrowave

The opticalThe opticalUVUVThe visibleThe visible

Infra-red (IR)Infra-red (IR)

X-rayX-ray

Gamma radiation Gamma radiation (nuclear-physical)(nuclear-physical)

101011-10-10-1 -1 metersmeters

1010-1-1-10-10-3-3 meters meters

200-400 nm200-400 nm400-750 nm400-750 nm

10-13000 cm10-13000 cm-1-1

1010-8-8-10-10-10-10 m m

1010-10-10-10-10-13 -13 mm

Change of electron spin Change of electron spin and nuclear spinand nuclear spin

Change of rotational Change of rotational conditionsconditions

Change of valence Change of valence electron conditionselectron conditions

Change of vibrational Change of vibrational conditionsconditions

Change of a condition Change of a condition of internal electronsof internal electrons

Nuclear reactionsNuclear reactions

3. The fundamental law of 3. The fundamental law of absorption.absorption.

sample

radi

atio

n so

urce

Reflection of light

Dispersion of light

luminescence

Light absorption

First law of light absorptionFirst law of light absorption Each thin layer of constant thickness of a Each thin layer of constant thickness of a

homogeneous environment absorbs an identical homogeneous environment absorbs an identical part of incident radiationpart of incident radiation

or:or: The part of the light which is absorbed by a The part of the light which is absorbed by a

homogeneous environment, is directly homogeneous environment, is directly proportional to a thickness of an absorbing proportional to a thickness of an absorbing layer:layer:

lkI

I1

Second law of light absorptionSecond law of light absorption

The part of the absorbed radiation is The part of the absorbed radiation is proportional to number of absorbing proportional to number of absorbing particles in volume of a solution, that is particles in volume of a solution, that is concentrationconcentration

CkI

I2

Bouguer-Lambert-Beer lawBouguer-Lambert-Beer law

Reduction of intensity of light which has Reduction of intensity of light which has passed through a layer of light-absorbing passed through a layer of light-absorbing substance is proportional concentration of substance is proportional concentration of this substance and a thickness of a layerthis substance and a thickness of a layer

klCo eII

Quantitative characteristics of Quantitative characteristics of absorptionabsorption

1. Transmittance - the ratio of the radiant power passing through a sample to that from the radiation’s source (T).

oI

IT

or

(I0) (I)

Diagram of Beer–Lambert absorption of a beam of light as it travels through a cuvette of width ℓ.

Optical density Optical density АА (Absorbance) (Absorbance)

AI

Ilg

I

IlgTlg o

o

An alternative method for expressing the attenuation of electromagnetic radiation is absorbance, A, which is defined as

or

Bouguer-Lambert-Beer lawBouguer-Lambert-Beer lawSo:So: The absorbanceThe absorbance of a solution is proportional to of a solution is proportional to

concentration of light-absorbing substance and a concentration of light-absorbing substance and a thickness of a layerthickness of a layer

OrOr The relationship between a sample’s absorbance

and the concentration of the absorbing species

lCA where: A – optical density (absorbance), ε – the molar absorptivity, C – concentration (molarity)

Additivity of optical densitiesAdditivity of optical densities Beer’s law can be extended to samples containing

several absorbing components provided that there are no interactions between the components. Individual absorbances, Ai, are additive. For a two-component mixture of X and Y, the total absorbance, Atot, is

k321 A...AAAA A = l(1С1 + 2С2 + …kСk)

SoSo

permeate (the molar absorptivity)

Iron (ІІІ) rhodanate 103

Complex Ti with H2O2 103

Complex Ti with chromotrope acid

105

Complex Cu with ammonia 5 102

Complex Cu with dithizon 5 104

Complex Al with aluminon 1,7 104

Complex Al with 2-stilbazole

3,5 104

Physical Limitations to Beer’s Physical Limitations to Beer’s LawLaw

NOTNOT monochromaticity of light: monochromaticity of light:

A = A = llС.С.

NOTNOT parallelism of light. parallelism of light. Temperature.Temperature. NOTNOT identical value of refraction of solutions. identical value of refraction of solutions. NOTNOT proportionality of a photocurrent and intensity of proportionality of a photocurrent and intensity of

a lighta light

Chemical Limitations to Beer’s Chemical Limitations to Beer’s LawLaw

Dilution of solution Dilution of solution (than more of reagent (than more of reagent excess, it is less deviation from the law);excess, it is less deviation from the law);

рН of mediumрН of medium: state of metal ion: state of metal ion

stability of complex ionsstability of complex ions competitivecompetitive reactionsreactions (for ligand) (for ligand) competitivecompetitive reactionsreactions (complexing agent) (complexing agent) polymerization and dissociationpolymerization and dissociation reactionsreactions ox-red reactionsox-red reactions

4. Electronic spectrum4. Electronic spectrum absorbance spectrum - a

graph of a sample’s absorbance of electromagnetic radiation versus wavelength (or frequency or wavenumber).

emission spectrum is a graph of emission intensity versus wavelength (or frequency or wavenumber).

5. Photometric method of analysis: an essence, 5. Photometric method of analysis: an essence, theoretical bases, usage in the pharmaceutical theoretical bases, usage in the pharmaceutical

analysisanalysis Molecular–absorption methodMolecular–absorption method is based on measurement of absorption by is based on measurement of absorption by

molecules (or ions) substances of electromagnetic radiation of an optical molecules (or ions) substances of electromagnetic radiation of an optical range:range:

ColorimetryColorimetry in which visible light was absorbed by a sample. The in which visible light was absorbed by a sample. The concentration of analyte was determined visually by comparing the concentration of analyte was determined visually by comparing the sample’s color to that of a set of standards using Nessler tubes (as sample’s color to that of a set of standards using Nessler tubes (as described at the beginning of this chapter), or by using an instrument called described at the beginning of this chapter), or by using an instrument called a colorimeter.a colorimeter.

PhotocolorimetryPhotocolorimetry - in which polychromatic light was absorbed by a - in which polychromatic light was absorbed by a samplesample

SpectrophotometrySpectrophotometry - in which monochromatic light was absorbed by a - in which monochromatic light was absorbed by a samplesample

UV - Spectrum (100-200 to 380-400 nanometers)UV - Spectrum (100-200 to 380-400 nanometers) Visible spectrum (380-400 to 780-800 nanometers)Visible spectrum (380-400 to 780-800 nanometers)

Block diagram for a double-beam in-timescanning spectrophotometer with photo of a

typical instrument.

Choice of optimum conditions of Choice of optimum conditions of spectrophotometry:spectrophotometry:

Choice absorption filters Choice absorption filters (in photometry)(in photometry) Choice of absorbanceChoice of absorbance

ААoptimaloptimal= 0.435= 0.435(less error) (less error)

А = 0.6 – 0.7А = 0.6 – 0.7 !!!! Not probably to measure absorbance!!!! Not probably to measure absorbance

2 < А < 0.032 < А < 0.03

Choice of thickness of a layerChoice of thickness of a layer - - not more 5 сmnot more 5 сm

А = А = l l C C

Way of transformation of a defined component in Way of transformation of a defined component in photometricphotometric compound compound

Choice of optimal wavelenghtChoice of optimal wavelenght ( (mmахах))

Sensitivity of photometric definitionSensitivity of photometric definition

А = А = l Cl C

CCminmin = А= Аminmin / / l l АА = 0.01 = 0.01 ll = 1 = 1 ccмм = 1000= 1000

thenthen ССminmin = 10 = 10-5-5 molmol//LL

Accuracy of photometric definitionAccuracy of photometric definition depends from:depends from:

Specific features of photometric reaction or Specific features of photometric reaction or photometric compoundsphotometric compounds

Characteristics of the used device (usually makes Characteristics of the used device (usually makes 1 - 2 %1 - 2 % relative) relative)

Methods of quantitative analysis:Methods of quantitative analysis:

1. A method of calibration1. A method of calibration chartchart

!!!!!! The method can be applied, if:The method can be applied, if: Structure of standard and investigated Structure of standard and investigated

solutions are similarsolutions are similar The interval of concentration on calibration The interval of concentration on calibration

chart should cover of defined concentrationchart should cover of defined concentration

2. Comparison method (a method on one standard)2. Comparison method (a method on one standard)

!! !! The method can be used if:The method can be used if: Dependence structure - property is strictly rectilinear and passes Dependence structure - property is strictly rectilinear and passes

through the beginning of co-ordinatesthrough the beginning of co-ordinates Concentration of standard and investigated solutions values of Concentration of standard and investigated solutions values of

analytical signals as much as possible similar and minimum analytical signals as much as possible similar and minimum differentdifferent

Structure of standard and investigated solutions are as much as Structure of standard and investigated solutions are as much as possible similarpossible similar

st

stхх A

СAС

х

dards

х

dards

A

A

С

C tantan

3. Method of molar or specific (concentration on 3. Method of molar or specific (concentration on % w/w) absorptivity% w/w) absorptivity

!! !! The method can be used if:The method can be used if: Strict linearity of dependence structure - an Strict linearity of dependence structure - an

analytical signal is observedanalytical signal is observed The analytical device maintains requirements of The analytical device maintains requirements of

metrological checkingmetrological checking

х

х

AC

E

AC х

х

4. Method of additives4. Method of additives

!!! The method can be applied, if:!!! The method can be applied, if: It is necessary to consider stirring It is necessary to consider stirring

influence of extraneous components of influence of extraneous components of sample on analytical signal of defined sample on analytical signal of defined substancesubstance

stх

х

stх

х

СС

С

A

A

хstх

хstх AA

AСС

Usage of UV – spectroscopy and Usage of UV – spectroscopy and spectrophotometry in visible spectrum:spectrophotometry in visible spectrum:

Identification and establishment of identity Identification and establishment of identity of drugsof drugs

Quantitative definition of substance contain Quantitative definition of substance contain Cleanliness check Cleanliness check The express control of the forged drugs The express control of the forged drugs Research of new substances structureResearch of new substances structure

66. . Multiwave spectrophotometryMultiwave spectrophotometry The absorbanceThe absorbance of any system containing of any system containing

limited number of painted limited number of painted components which components which chemically one don’t react with anotherchemically one don’t react with another, , is is equal sum of absorbance of mix componentsequal sum of absorbance of mix components at the same wavelength:at the same wavelength:

nAAAA ...21

Each Each ““partialpartial”” absorbanceabsorbance is equalis equal

lCA iii

1. Analysis of two componential mix, when 1. Analysis of two componential mix, when light absorption curves both substance light absorption curves both substance bridge along all spectrum, but on it is bridge along all spectrum, but on it is partite maximums of absorptionpartite maximums of absorption

If we consider Beer’s LawIf we consider Beer’s Law

lClCA

lClCA

2211

2211

222

111

22

111

212

21

AAA

AAA

Molar absorptivity of first componentMolar absorptivity of first component

lcA 111 11

lc

A

1

11

1

1

Molar absorptivity of another componentMolar absorptivity of another component

lcA 222 11

lc

A

2

22 1

1

The obtained results is substituted into The obtained results is substituted into system of the equations and solve it. Its system of the equations and solve it. Its decision can be presented next formulas :decision can be presented next formulas :

;1221

1221

2121

221

AAC

.1221

2112

2121

112

AAC

Optimal conditions for two-wave Optimal conditions for two-wave spectrophotometryspectrophotometry

Percentage error Percentage error С/СС/С must be the least, must be the least, value of absorbances must be in the range of value of absorbances must be in the range of 0,3-1, and ratio 0,3-1, and ratio

must be maximalmust be maximal

2221 1221 /_/ and

Modern spectrophotometerModern spectrophotometer for UV and visiblefor UV and visible spectrumspectrum

2. 2. Analysis of two componential mix, Analysis of two componential mix, when light absorption curves both when light absorption curves both substance bridge, but on it is spectral substance bridge, but on it is spectral range, where absorption one of substance range, where absorption one of substance may neglectmay neglect

In this case concentration of first In this case concentration of first substance is calculated on substance is calculated on measured absorbance measured absorbance АА at at wavelength wavelength 11::

)./(1111 lAC

Concentration of second substance in mix is Concentration of second substance in mix is calculatedcalculated through concentrationthrough concentration С С11

l

lCAC

lClCA

2

2

222

2

1212

2211 ;

3. 3. Analysis of two componential mix, when Analysis of two componential mix, when it is separate maximums of light it is separate maximums of light absorption for each substance in absorption for each substance in spectral rangespectral range

l

AC

1

1

11

at wavelength 1

at wavelength 2 l

AC

22

22

77. . Differential spectrophotometryDifferential spectrophotometry

Differential spectrophotometry is used for:Differential spectrophotometry is used for:

Increases of precision of analyses precision of analyses at definition of considerable quantities of substance;

For elimination of extraneous influence of another components and an exception of reagent absorption.

Normal spectrophotometry Differential spectrophotometry

Essence of differential Essence of differential spectrophotometry:spectrophotometry:

Absorbances of investigated and standard Absorbances of investigated and standard solution are measuredsolution are measured on ratio to solvent on ratio to solvent investigated component with concentration investigated component with concentration СС00 (it is low fidelity equal concentration of (it is low fidelity equal concentration of

investigated solution) investigated solution) instead of ratio to pure instead of ratio to pure solventsolvent (its absorbance is equal practical (its absorbance is equal practical zero)zero)

Main characteristic of absorption in Main characteristic of absorption in differential spectrophotometrydifferential spectrophotometry

Ratio of light intensities Ratio of light intensities

is named is named conditional conditional transmittancetransmittance

comparisonI

I x

compar

хrelativeх І

ІТ _

Relative (conditional) Relative (conditional) transmittancetransmittance

compar

хrelativeх Т

ТТ _

AT lg

compor

х

оcompar

ох

comparison

хrelativeх Т

Т

ІT

ІТ

І

ІТ

_

Measured experimentally absobance is Measured experimentally absobance is difference of absorbances of investigated difference of absorbances of investigated solution and comparison solution.solution and comparison solution.

comparхrelativeх

comparхrelativeх

АlСА

ААА

_

_ ,

lCCАlСА xcomparхrelativeх )( 0_

Quantitative analysisQuantitative analysis:: A method of calibrationA method of calibration chartchart Calculated methodCalculated method (modified (modified comparison comparison

methodmethod))

conparcomparsrelats

relatхх

compards

comparх

relatст

relatx

СССА

АС

СС

СС

А

A

)(

,

tantan_

_

tan_

_

Advantage of Advantage of differential differential spectrophotometryspectrophotometry

Considerable range expansion of defined Considerable range expansion of defined contents (high concentration);contents (high concentration);

Relative error is equal 0,05-2 %, that much more Relative error is equal 0,05-2 %, that much more low, than in photometry.low, than in photometry.

88. . The extraction-photometric The extraction-photometric analysisanalysis (EPMA)(EPMA)

it isit is hybridhybrid method of analysismethod of analysis, , in whichin which combinecombine extractionextraction ( (asas methodmethod excretion, excretion, separation and concentratingseparation and concentrating) ) andand spectrophotometryspectrophotometry

EPMA is usedEPMA is used, , whenwhen::

analyze analyze complex mixcomplex mix define define substancesubstance, which is , which is slightly solubleslightly soluble in in

waterwater, but , but freely solublefreely soluble in select organic solventin select organic solvent define define substancesubstance, which is , which is very small quantity into very small quantity into

investigated objectinvestigated object define define impurities in presence main componentsimpurities in presence main components immediately definition investigated component is immediately definition investigated component is

impossible (impossible (light absorption curves both substance light absorption curves both substance bridge along all spectrumbridge along all spectrum))

define define colourless substancecolourless substance (use coloured extraction (use coloured extraction reagent)reagent)

ChoiceChoice of photometric reactionof photometric reaction inin EPMAEPMA::

Photometric reaction of formationPhotometric reaction of formation colouredcoloured metal complexesmetal complexes::

PbPb2+2+ + 2 + 2HH22DzDz = = PbPb((HDzHDz))22 + 2+ 2HH++

extractionextraction inin CHClCHCl33

oror CClCCl44

maxmax= 520 nm= 520 nm (= 7(= 7101044))

Photometric reaction of ionic associate Photometric reaction of ionic associate formationformation

[[SbClSbCl66]]-- + + RR++ = = RR++[[SbClSbCl66]]--

extractionextraction in in toluenetoluene oror benzenebenzene

RR – – acidic or basic dyeacidic or basic dye maxmax= 660 = 660 nmnm (= 5(= 5101044))

Extraction has Extraction has extraction efficiency equalextraction efficiency equal R=99,9%R=99,9% is necessary for usage of is necessary for usage of extraction-photometric method of analysis extraction-photometric method of analysis thatthat

It receive It receive by choiceby choice:: Solvent-extracting agentSolvent-extracting agent Extraction reagentExtraction reagent Photometric reactionPhotometric reaction Chemical factors of extraction (рН, ionic Chemical factors of extraction (рН, ionic

strength, solution composition)strength, solution composition)

Advantages ofAdvantages of Е ЕPPМА:МА: High sensitivityHigh sensitivity, because of:, because of:

- high molar - high molar absorptivity of extracted complexes of extracted complexes

- concentrating of solution by extraction method- concentrating of solution by extraction method High selectivityHigh selectivity (pre-award separation, (pre-award separation,

excretion of defined component from mix)excretion of defined component from mix) Rapid analysisRapid analysis (in comparison with classical (in comparison with classical

method of precipitation) method of precipitation) Relative simplicity of instrumentation Relative simplicity of instrumentation

((separatory funnel, spectrophotometer), spectrophotometer)

Usage of ЕPМА in analysis of Usage of ЕPМА in analysis of pharmaceutical drugs:pharmaceutical drugs:

define majority of metal ions define majority of metal ions (complexing (complexing agent)agent)

define majority of substance, which is define majority of substance, which is insoluble in waterinsoluble in water (Trimethoprimum in (Trimethoprimum in composition of Biseptolum)composition of Biseptolum)

define impurities in drugs define impurities in drugs (salicylic acid in (salicylic acid in Aspirinum)Aspirinum)

define biological-active substance in drugs define biological-active substance in drugs (from (from medicinal herbs)medicinal herbs) (heart glycosides, (heart glycosides, alkaloids, flavanoids, components of essence)alkaloids, flavanoids, components of essence)

9. Photometric titration9. Photometric titration

Photometric titration is titration method in Photometric titration is titration method in which end point of titration (e.p.t) is which end point of titration (e.p.t) is determined by photometry or determined by photometry or spectrophotometry method.spectrophotometry method.

Method isMethod is based on determination e.p.t based on determination e.p.t on on jump of solution absorbance jump of solution absorbance in equivalence in equivalence point.point.

Condition of titrimetric reaction usage Condition of titrimetric reaction usage in in spectrophotometry is linear spectrophotometry is linear relation between absorbance and relation between absorbance and concentrationconcentration

А = А = l C l C

Reactions which is used in spectrophptometric Reactions which is used in spectrophptometric titrationtitration::

Acid-baseAcid-base

ComplexingComplexing

RedoxRedox

Calculation of titrant volumeCalculation of titrant volume::

On titration curveOn titration curve

On system of the equationsOn system of the equations::

..11.. pepe VbaA

..22.. pepe VbaA

21

12.. bb

aaV pe

Curves of specrtofotometric titrationCurves of specrtofotometric titration can can be the be the different formdifferent form. Their character depends . Their character depends on what components of reaction absorb at the on what components of reaction absorb at the chosen wavelength.chosen wavelength.

А + В А + В АВ АВChange of solution absorbance is defined by Change of solution absorbance is defined by

value of molarvalue of molar absorptivityabsorptivity

ABAB

PhotometricPhotometric titrationtitration curvecurve ofof solution solution FeFe2+2+ by standard solution of by standard solution of KK22CrCr22OO77

V (K2Cr2O7)

A

e.p.

PhotometricPhotometric titrationtitration curvecurve ofof solution solution KMnOKMnO44 by standard solution ofby standard solution of FeFe2+2+

V (Fe2+)

A

e.p.

The spectrophotometric titration can be applied The spectrophotometric titration can be applied whenwhen

TitrantTitrant or or defined substancedefined substance or or product of product of reactionreaction absorb lightabsorb light. .

If titrant or defined substance or product of If titrant or defined substance or product of reaction reaction don’t absorb lightdon’t absorb light so we so we use indicatorsuse indicators – substances, which don’t absorb light, but form – substances, which don’t absorb light, but form compound with defined substance (АInd), titrant compound with defined substance (АInd), titrant (ВInd) or a reaction product (АВInd) which (ВInd) or a reaction product (АВInd) which absorb lightabsorb light

As during titration occur As during titration occur solution dilution solution dilution in in cell (cuvette), than for taking into account of cell (cuvette), than for taking into account of solution volume increase is necessary to plot solution volume increase is necessary to plot of photometricof photometric titrationtitration curve on coordinate curve on coordinate ААcorrectedcorrected – С – С

0

.0

V

VVАA titrant

measuredcorrected

Advantages of specrophotometricAdvantages of specrophotometric titrationtitration::

The higher selectivity and possibility definition The higher selectivity and possibility definition of several components of sample;of several components of sample;

Possibility of Possibility of titration of the paintedtitration of the painted solutions; solutions; The higher sensitivityThe higher sensitivity in comparison with in comparison with

classical method of analysisclassical method of analysis Possibility of Possibility of usage of reactions which don’t usage of reactions which don’t

come to an end in e.p.come to an end in e.p. or reactions which have or reactions which have small equilibrium constantsmall equilibrium constant

The higher accuracyThe higher accuracy

Thanks for your attention!Thanks for your attention!