uv application

8/12/2019 UV Application

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Applications:1. Structural Analysis2. Identification of Drugs (Pharmacopoeial)

3. Limit Test

4. Quantitative Analysis (Assay)5. Study of Kinetics

6. Determination of pKaof Indicators

7. Determination of Complex Composition8. Determination of Molecular Weight of

Compound

9. As HPLC Detector


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10. Forensic Application11.Applications in Preformulation and

Formulation

Partition Coefficient

Solubility

Release of Drug from Formulation


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1. Structural Analysis: Chromophoric part is required for absorbance. Change in chromophoric part produces predictable change

in absorption property.

Eg.:

1.Detection of Conjugation:

It helps to show the relationship between different groupsparticularly with respect to the conjugation.

a) Between two or more carbon-carbon double (or triple)bonds

b) Between carbon-carbon and carbon-oxygen doublebonds

c) Between double bonds and an aromatic ring.


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2.Detection of Geometrical Isomers:

Trans isomers exhibit max at slightly

longer wavelength than the cis isomer For e.g.,

Of the two stilbenes the trans isomers

show max = 294nm while the cisisomer show max = 278 nm.


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3.Detection of Functional groups: That is possible to detect the

functional groups with the help of UV

Spectrum.

For e.g.,

Absence of absorption above 200nmsays that there is absence ofconjugation, carbonyl group and

benzene ring in the compound.


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2. Identification of Drugs: Some of the drugs which are official in

pharmacopoeia have specific max value atwhich they give higher value of absorbance.

So from that drug can be easily identified.

For e.g.,

1.PCM should have max =

249nm and

absorbance 0.44

2.Morphine sulphate should have max =

298nm.


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3. Limit Test:

It is one of the best methods fordetecting impurities in inorganiccompounds.

The band due to impurities are veryintense.

For e.g.,

Impurity having amount 0.05% has an value of 2000so impurity can beidentified in a transparent major

component.


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4. Quantitative Analysis: The method can easily detect the quantity with the

sensitivity of g/ml.

By applying the mathematical equation theconcentration can be detected from theabsorbance value.

For e.g.,

A = abc

Where, A = Absorbance

a = Specific absoptivity

b = Pathlength

c = Concentration


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5. Study of Kinetics: It can be used to study the kinetics of

reaction.

In it, the change in concentration either of a

reactant or product with time is measured.The method is based upon the fact that the

one of the reactants or products exhibiting

suitable absorption in the UV region is notoverlapped by other species.

It can be applicable to such rate which must

be relatively slow.


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6. Determination of pKaof Indicators:Acid-Base indicators are weakly acidic or

basic compounds.

To the reference of pH equation, the pKa canbe calculated if the ratio of [HA]/[A-] isknown at particular pH.

The ratio can be determinedspectrophotometrically from the graphwhich is plotted between absorbance and

wavelength at different pH value.


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7. Determination of Complex

Composition:

Transition metal complexes are measured by

U.V. Visible absorption spectroscopy as theyform colored complexes.

For e.g.,

1.Fe+2forms violet color with salicylic acid.2.Ni+2forms green color with dimethyl

glyoxime.


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8. Determination of Molecular Weightof Compound:It is limited to special compounds like

C=O, R-NH2, etc.E.g.,

If

of chromophore is50,000

andconcentration of solution of solution ofsulpha drug is 5g/ml. Find out molecularweight of drug. Absorbance = 0.4


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We require concentration in moles/litre.

5g/ml = 5 10-6 103gm/L = 5 10-3gm/L Molarity = 5 10-3moles/L. M= mol. wt.

M

A = bc A = 0.4, b = 1, c = 5 10-3, = 50000

M

.. 0.4 = 50000 1 5 10-3

M

.. M = 50000 0.005

0.4

.. M = 625


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9. As HPLC Detector:HPLC gives most efficient separation. In modern analysis, HPLC is combined with

detectorsHPLC and U.V. visible is commonly used in

combination for specific drug subs.

E.g. :- Cotrimoxazole

1. Sulfamethoxazole max= 257nm

2. Trimethoprime max= 267nm


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10. Forensic Applications: UV/Vis molecular absorption is routinely used in the

analysis of narcotics and for drug testing.

One interesting forensic application is the determinationof blood alcohol using the Breathalyzer test.

In this test a 52.5-ml breath sample is bubbled through anacidified solution of K2Cr2O7.

Any ethanol present in the breath sample is oxidized by thedichromate, producing acetic acid and Cr3+ as products.

The concentration of ethanol in the breath sample isdetermined from the decrease in absorbance at 440 nmwhere the dichromate ion absorbs.

A blood alcohol content of 0.10%, which is the legal limit inmost states, corresponds to 0.025mg of ethanol in the

breath sample.


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11. Applications of UV/Vis. In

Preformulation and Formulation: U.V./Visible spectrophotometry is a standard

method for determining the physico-chemicalproperties of drug molecules prior toformulation and for measuring their release fromformulation.

The type of properties which can be usually

determined by the UV method are listed here:Partition Coefficient

Solubility

Release of a Drug from a Formulation.


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Partition Coefficient:The partition coefficient of a drug betweenwater and an organic solvent may bedetermined by shaking the organic solvent

and the water layer together and determiningthe amount of drug in either the aqueous ororganic layer by UV spectrophotometry.

If buffers of different pH values are used, thevariation of partition coefficient with pH maybe determined and this provides anothermeans of determining the pKa value of a

drug.


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SolubilityThe solubility of a drug in, for instance,water may be simple determined by shaking

the excess of the drug in water or bufferuntil equilibrium is reached and then usingUV spectrophotometry to determine the

concentration of the drug that has gone intosolution.


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Another method for determining solubility, where

an ionisable group is present in the drug, is todissolve varying concentrations of the salt of thedrug in water and then excess acid to a solution ofthe salt of an acidic drug or excess base to a

solution of the salt of the basic drug, thusconverting the drugs into their un-ionised forms.

When the solubility of the un-ionised drug in

water is exceeded, a cloudy solution will result andUV spectrophotometry can be used to determineits degree of turbidity by light scattering, whichcan be measured at almost any wavelength, e.g.

250nm.


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Release of a drug from a

formulation: UV spectrophotometry is used routinely to monitor in

vitro release of active ingredients from formulations.

For simple formulations the drug is simply monitoredat its max.

In the example shown in figure, the rate release ofpseudoephedrine from a controlled release

formulation was monitored. The release of the drug was followed by monitoring its

release into distilled water using a UVspectrophotometer set at 206nm.


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In the example given in figure, the particle size of theethylcellulose used in the formulation affected the rateof release.


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If UV-absorbing excipients were present insuch a formulation, the UV wavelength usedfor monitoring release would need to beselected carefully or HPLC coupled to UV

detection might be used.For such studies, the sampling of the

dissolution medium may be fully automated

so that the medium is filtered and pumpedthrough the UV spectrophotometer at settime intervals in order to take a reading.

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