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ATTENUATED TOTAL REFLECTANCE SPECTROSCOPY

PRESENTED BY: SAMIKSHA SAWANT

M.PHARM(IP), 1st SEM GUIDED BY :

DR.SUPRIYA MAHAJAN

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INFRARED SAMPLING METHODS

Transmission

Internal Reflection

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WHY ATR?

ATR generally allows little or no sample preparation, which greatly speeds sample analysis.

It allows very thin sampling pathlength and depth of penetration of the IR beam into the sample.

Useful for samples that are too thick to be analysed bt transmission and those that strongly absorb radiation

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1 2

3 4

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WHAT IS ATR?

An evanescent wave is a penetrating electromagnetic field whose intensity quickly decays as it moves away from its source. An evanescent beams interacts with the sample, sample absorbs energy.Thus there is reduction in the intensity of the reflected wave reaching the detector.

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MATERIALS ATR SPECTRAL

RANGE (cm-1)

REFRACTIVE INDEX

DEPTH OF PENETRATION

(microns)

Germanium

5500-675 4 0.66

Silicon 8900-1500 &

360-120

3.4 0.85

AMTIR 11,000- 725

2.5 1.77

ZnSe 15000-650 2.4 2.01

Diamond 25000-100 2.4 2.01

MATERIALS USED FOR MAKING ATR CYRSTAL

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FACTORS AFFECTING THE SPECTRUM

Refractive indices of the ATR crystal and the

sampleAngle of incidence of the IR beamCritical angleDepth of penetrationWavelength of the IR beamEffective pathlengthNumber of reflectionsQuality of the sample contact with ATR crystalATR crystal characteristic

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1) REFRACTIVE INDEX OF CYRSTAL AND SAMPLE

The refractive indices of the crystal and sample are important considerations in the ATR sampling technique by virtue of the following equation,

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2) THE CRITICAL ANGLE

Total internal reflection critical angle - when the angle of refraction (r)

becomes equal to 90 degrees and Snell's law reduces to:

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3) THE DEPTH OF PENETRATION (DP) OF THE IR BEAM INTO THE SAMPLE

Further useful consideration for ATR analysis is the depth ofpenetration (dp) of the IR beam into the sample.The depth of penetration is given by:

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4) EFFECTIVE PATH LENGTH:

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5) QUALITY OF SAMPLE CONTACT WITH THE ATR CRYSTAL:

Intimate contact of the sample be made onto the surface of the ATR crystal.

For rigid, irregular shaped or porous samples, high pressure sufficient to deform the sample will increase the extent of sample contact and thereby increase sample absorbance.

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SAMPLING

Analysing liquids

Analysing solids

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APPLICATIONSIdentification of functional groups and drug substances

Used in identification of paints, varnishes

Useful for substances that are difficult to handle by conventional sampling technique- rubber, cured resins etc.

Used in forensic and biomedical fields

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CASE STUDY: Identification and Characterization of Toxicity of Contaminants in Pet Food Leading to an

Outbreak of Renal Toxicity in Cats and Dogs

HPLC and MS, which revealed

presence of melamine and cyanuric acid

Infrared spectroscopy on

individual crystals from cat

kidneys confirmed that

they were melamine-

cyanuric acid cocrystals.

Pathological evaluation of cats and dogs that had died

from the acute renal failure indicated the presence of crystals in

kidney tubules. 

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These spectra were obtained using an infrared microscope equipped with a 20× ATR objective. The

germanium ATR crystal has a contact area of approximately 100 μm. The reference compound was

prepared by cocrystallization from solutions of melamine and cyanuric acid

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CONCLUSION

ATR is a powerful IR sampling technique that provides excellent quality data in conjunction with the best possible reproducibility

It has revolutionized IR solid and liquid sampling through faster sampling

Minimizes user to user variations

Has versatality and is non destructive technique for variety of materials- soft solid materials, liquids, powders, gels, pastes, polymers etc.

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REFERENCEShttp://toxsci.oxfordjournals.org/content/

106/1/251.fullhttp://old.vscht.cz/anl/vibspec/FTIR%20Reflection

%20Techniques.pdfhttp://www.utsc.utoronto.ca/~traceslab/

ATR_FTIR.pdfhttp://www.piketech.com/files/pdfs/ATRAN611.pdf Handbook of analytical instruments, R S Khandiur,

170-173Instrumental Methods of Analysis, Willard, Merritt,

Dean and Settle, seventh edition, 311-315Analytical Chemistry Handbook, John A. Dean, 6.16-6.20Instrumental Methods of Analysis, Dr. Supriya S.

Mahajan, 63-70

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THANKYOU!