FTIR ATR AND NIR

FTIR ,ATR AND NIR INSTRUMENTATION AND APPLICATIONs: 

FTIR ,ATR AND NIR INSTRUMENTATION AND APPLICATIONs PRESENTED BY MS.DIPALI S.PATEL M.PHARM SEM – 1(QA) ROLL NO: 3 GUIDED BY MR.DHARMENDRA A.BARIA M.PHARM (PHARMACEUTICAL CHEMISTRY) ASSISTANT PROFESSOR DHARMAJ DEGREE PHARMACY COLLEGE, DHARMAJ 1

Fourier Transform (FTIR) instrument: 

Fourier Transform (FTIR) instrument simple IR spectra is plot of wave no  %T and called as frequency domain spectra while FTIR is time domain spectra. Fourier transform is used to convert time domain spectra to frequency domain spectra. Then time is converted to wave no. Fourier transform mathematical model is operated by computer. Encodes the information in an interferogram using a Michelson interferometer 2

components: 

components Source Michelson Interferometer: Beam splitter Fixed mirror Moving mirror at constant velocity Sample Detector 3

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1 . Source :- Same as IR 2. Beam Splitter :- It is made of material which has 50%refractive index a) For far IR :- Mylar film sandwiched between halide plate of low refractive index solid used. b) For Middle IR :- Thin film of germanium or silicon deposited on CsI or CsBr or KCl or NaCl c) Near IR :- Thin film of ferric oxide deposited on calcium chloride. 3. Detector :- Pyroelectric detector or photon detector used. Thermal detector is not used because of low sensitivity 4. Modulator :- They are required to convert high frequency radiation to low frequency radiation because high frequency radiation is not detected by detector. 4

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5 Michaelson Interferometer : 10 14 Hz is too fast for the rapid changes in power to be directly measured as a function of time. Interferometer creates a replicate interference pattern at a frequency that is a factor of 10 10 times slower 10 4 -10 5 Hz can be measured electronically f = (2v m /c)n = 10 -10 n, v m = 1.5 cm/s

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Optical Diagram of Michelson Interferometer-Light Path Stationary Mirror moving mirror d mirror drive unmodulated incident beam beam splitter Modulated exit beam retardation T R T R sample Detector

FT-IR detectors: 

FT-IR detectors Pyroelectric transducers (PTs): Pyroelectric substances act as temperature-dependent capacitors Triglycine sulfate is sandwiched between two electrodes. One electrode is IR transparent The current across the electrodes is Temperature dependent PTs exhibit fast response times, which is why most FT instruments use them 7

Photo conducting transducers:: 

Photo conducting transducers: Thin film of a semi-conducting material IR radiation promotes non-conducting electrons to a higher energy conducting state. The voltage drop across the thin film is a measure the Power of the IR beam. PbS for near IR can be operated at RT Hg/Cd/Te can be used in the mid-IR and far IR, but must be cooled to 77 K Superior response characteristics Great for GC-IRs 8

Operation of FTIR Spectrometer: 

Operation of FTIR Spectrometer The overall path of the two light beams determines the degree of constructive or destructive interference upon reflection to the detector. The beam from the source is modulated by the interferometer, directed to the sample measured at the detector. When recombined at the beam splitter each beam has undergone one external reflection (R) and one transmission (T). The output beam from the interferometer depends on optical path differences (d ) After the data are detected and stored, it is necessary to perform a mathematical transform operation (a Fourier Transform) on the data set to convert it into a conventional spectrum. 9

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Interferometer He-Ne gas laser Fixed mirror Movable mirror Sample chamber Light source (ceramic) Detector (DLATGS) Beam splitter FT Optical System Diagram 10

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Monochromatic light from source strikes on a beam splitter B ,it splits beam in exactly two half. - One half is transmitted as beam C to fixed mirror (D) and reflected back to B. The other half is transmitted as beam E to movable mirror (F) and reflected back to B. Both of these beams are recombined. Constructive interference when distance between fixed mirror and movable mirror is equal from beam splitter ,the emergent beam is in in-phase with that from the stationary mirror and constructive interferes takes place with high intensity radiation reach to detector. Destructive interference  when moveable mirror moves away from the equidistant point by factor of λ / 4 , the distance is altered by λ /2 and reflected radiation is out of phase with that from the stationary mirror and destructive interferes takes place with low radiation intensity reach to detector. 11

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Destructive interference

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Constructive interference

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15 The signal at the detector as a function of path length difference for monochromatic light. In practice, the mirror in one arm is kept stationary and that in the second arm is moved slowly. As the moving mirror moves, the net signal falling on the detector is a cosine wave with the usual maxima and minima when plotted against the travel of the mirror. The frequency of the cosine signal is equal to where f is the frequency; v, the velocity of the moving mirror; and l, the wavelength of radiation. The frequency of modulation is therefore proportional to the velocity of the mirror.

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16 Real IR sources are polychromatic. Radiation of all wavelengths generated from the source travels down the arms of the interferometer. Each wavelength will generate a unique cosine wave; the signal at the detector is a result of the summation of all these cosine waves.

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The beam finally arrives at the detector and is measure by the detector. The detected interferogram can not be directly interpreted. It is decoded into sample spectra by ″ Fourier transform equation” - The computer can perform the Fourier transformation calculation and present an infrared spectrum, which plots transmittance vs wave number 17

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Fourier Transform of Single Mode 18

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Selectivity: Offers much more selectivity that UV-VIS spectroscopy Absorption peaks are narrow in comparison and the energies of the absorption bands are unique for sets of functional groups Thus qualitative information is readily obtained from IR spectra Correlation charts and compilations of IR spectra for unknown matching But IR spectra do not have the specificity that NMR spectra or electron impact mass spectra tend to exhibit 19

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Sensitivity: This is perhaps the major shortcoming of this technique when compared to fluorescence, or especially mass spectrometry However, Beer’s law type analysis are possible and fairly routine using FT-IR Detection limits are in the ppm range ( μ m) 20

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Advantage of FTIR instrumentation over dispersive IR : Inexpensive, reliable, fast Easy to maintain, sensitive Improved frequency resolution Improved frequency reproducibility (older dispersive instruments must be recalibrated for each session of use) Computer based (allowing storage of spectra and facilities for processing spectra) Easily adapted for remote use (such as diverting the beam to pass through an external cell and detector, as in GC - FT-IR) Internally Calibrated: These instruments employ a HeNe laser as an internal wavelength calibration standard. These instruments are self-calibrating and never need to be calibrated by the user. 21

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Ultrafast FTIR Spectrometer: 

Ultrafast FTIR Spectrometer A very rapid scan FTIR instrument has been built which allows time-resolved measurements of single transient events on the millisecond time-scale. The device is capable of recording more than 1000 complete scans per second at 4 cm -1. Uses a apinning disk mirror which varies the retardation time with extreme rapidity. 23

ATR (Attenuated Total Reflectance): 

ATR (Attenuated Total Reflectance) Attenuated total reflectance (ATR) is a sampling technique used in conjunction with infrared spectroscopy which enables samples to be examined directly in the solid,liquid or gas state without further preparation. 24

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25 Principle This technique is based upon the fact that reflected radiation slightly penetrates the surface from which it is reflected. Refractive index of the cell(ATR crystal) is greater than that of the sample medium and the angle is greater than the critical angle, the infrared light beam will suffer total internal reflectance at the interface. But the beam of Light travels short distance(less than 2 μ m) in to lower refracting index material(sample).This penetrating beam is called as an evanescent wave . If medium absorbs some of the light the reemerging beam will be attenuated, that is reduced in intensity ,so it is called as ATR. The interaction of evanescent wave with the sample essentially provide an IR spectrum of sample.

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28 Snell’s law for calculate angle of refraction n 1 sin α = n 2 sin β n 1 & n 2 = refractive index of 1 st and 2 nd medium b= angle at which the radiation reflected If n 2 is less than n 1 , an angle a exists for which b is 90º, that is, for which the radiation is completely reflected. That angle is the critical angle θ c . θ c can be calculated for below equation where b is 90º n 1 sin θ c = n 2 sin 90º Θc = sin -1 n 2 /n 1

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29 MATERIALS SPECTRAL RANGE (cm -1 ) REFRACTIVE INDEX PENETRATION DEPTH Germanium 5,500-675 4 0.66 Silicon 8,900-1,500 3.4 .85 AMTIR 11,000-725 2.5 1.77 Znse 15,000-650 2.4 2.01 Diamond 30,000-200 2.4 2.01 Commen ATR Materials used AMTIR is composed of Ge, Se and As

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Application :- Used identification of paints, varnish. Useful for substances that are difficult to handle in a convetional manner.eg.rubber and cured resins. Used in examining art work & artifacts. used in forensic science. It is used to monitor organic reactions 30

NIR(NEAR INFRARED SPECTROSCOPY): 

NIR (NEAR INFRARED SPECTROSCOPY) NIR is a spectroscopic method that uses the near-infrarad region of the electromagnetic spectrum (from about 800 nm to 2500 nm). Near-infrared spectroscopy is based on molecular overtone and combination vibrations. Such transitions are forbidden by the selection rules of quantum mechanics. As a result, the molar absorptivity in the near IR region is typically quite small. 31

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One advantage is that NIR can typically penetrate much farther into a sample than mid infrared radiation. Near-infrared spectroscopy is, therefore, not a particularly sensitive technique, but it can be very useful in probing bulk material with little or no sample preparation. The molecular overtone and combination bands seen in the near IR are typically very broad, leading to complex spectra; it can be difficult to assign specific features to specific chemical components. Multivariate (multiple wavelength) calibration techniques (eg. principal components analysis, partial least squares, or artificial neural networks ) are often employed to extract the desired chemical information. Careful development of a set of calibration samples and application of multivariate calibration techniques is essential for near-infrared analytical methods. 32

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Instrumentation Instrumentation for near-IR (NIR) spectroscopy is partially similar to instruments for the visible and mid-IR ranges. Source Quartz halogen light Light emiting diodes Dispersive element Prism Diffraction grating Interferometer(FT NIR) Detector Silicon based ccds In GaAS(in diode array instrument) 33

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Applications Medical uses Medical applications of NIRS center on the non-invasive measurement of the amount and oxygen content of hemoglobin , as well as the use of exogenous optical tracers in conjunction with flow kinetics. 2. Determination of particle size in USP grade Aspirin. 3. Determination of blend uniformity. 4. Determination of active ingredients in multicomponent dosage forms 5. Determination of Polyforms . 6. Moisture determinations 34

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35 REFERENCES: James Robinson, ‘Undergraduate Instrumental analysis, Marcel Dekker Publication, Page no: 255,274. Skoog, Holler & Niemann ,“Application of U.V Spectroscopy”, Principles of Instrumental Analysis, Fifth Edition , Saunders Brace College Publisher, Page no:392,393,422. Devid G. Watson, ‘Pharmaceutical analysis’, Chuechill Livingstone,Page no:112 to 116. http://www.wcaslab.com/TECH/tbftir.htm http://www.ides.com/articles/testing/2008/FTIR_Analysis.as http://en.wikipedia.org/wiki/Fourier_transform_infrared_spectroscopy#Bac...

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36 THANK YOU