Instrumentation of IR spectroscopy

1. INSTRUMENTATION OF IR SPECTROSCOPY
Presented by
Randeep Patro
M.Pharm(Pharmacology)
SCHOOL OF PHARMACEUTICAL SCIENCES
SIKSHA ‘O’ ANUSANDHAN (DEEMED TO BE UNIVERSITY) , BHUBANESWAR

2. a)Dipersive [ 1]
• Many moving parts causing
mechanical slippage.
• Stray light causes superior
reading.
• Slow scan speed
• Only narrow frequency of
radiation falls at a time.
• Sample is subjected to thermal
effect
b)Nondispersive [ 3]
• Used in the sample containging
carbon monoxide like gases.
• Very rarely used now a days
• Chopper providing low response
to noise ratio .

3. c) FTIR [4]
He-Ne laser is used to control the
velocity of the moving mirror.
Advantages
• stray light does not affect the detector
• A much larger beam used at all the times:
data collectio is easier.
• Rapid scan enables to monitor undergoing
changes in the sample
• Emission of IR by the sample will not
be detected.
• Only the mirror moves during an exp.
• Sample is not subjected for thermal
effect .

5. SOURCE OF RADIATION
It must have the fallowing ideal properties
• Intense enough for detection
• Steady source
• Extended over the desired wavelengths
a) Nernst Glower[2]
Diameter 1-3mm and length 2-5cm
Temp of 1000 to 1800◦ C
Emits max. radiation of 7100 cm-1
Disadvantage :
• The intensity of radiation remains steady and const over longer period of time
• It emits IR over wide wavelength range
• It has frequent mechanical failure
• Its energy is concentrated in the visible and near IR region of spectrum

6. b) Globular Source[2]
Diameter 5mm and length 5cm
Heated upto 1300 to 1700◦ C
Emits max. radiation of 5200 cm-1
Advantage :
• It is self starting
• Its temp coefficient is positive .it can be controlled with a variable
transformer
• It works at wavelengths longer than 0.15 µ
c) Incandescent Wire Source[3]
Lower intensity but longlife than nernst & Globular
Heated upto 1100k
No cooling require and maintenance free
Advantage :
• It fails in Far IR region because it is glass enclsoed and has a low
emission spectra

7. d) Mercury Arc Source[2]
In the far IR region (wave number <200 cm-1 )
it loses its effectiveness so a high pressure
mercury lamp are used
e) Tungsten Filament Lamp[3]
Convenient source for near IR region i.e 0.8-2.5µm
f) Nicrome Wire [2]
Heated Of surface temp 800-900◦C
Nicrome wire lamp Tungsten Filament Lamp

8. Monochromators
It achieve the desired frequency from radiation source
monochromators are used.
Two Types :
a) Prism [1]
Metal halide Prisms and NaCl Prisms are used
Two types :
single pass double pass

9. b) Grating[2]
240 lines per nm and
120 lines per nm
Sampling techniques :
1) Solid Sampling – solids run in solution, solid films, mull technique , pressed pallet
2) Liquid Sampling
3) Gas Samping – Gas absorption cells
Sample cell[3]

10. DETECTORS
a)Bolometer [1]
Response time = 4msec
Resistance increases = 0.4% per every ◦C
b)Thermocouples[1]
Response time = 60msec
To increase sensitivity Thermophyles
are used

11. c) Thermistors[1]
Fused mixture of metal oxides
Resistance changes = 5% per ◦C
d)Golay Cell[1]
Response time = 10-2 sec

12. e)Photocoductivity Cell[2]
Response time = 0.5msec
Limited to near IR region
f) Semiconductor Detector[2]
Insulator to Conductor time = 1msec
g)Pyroelectric Detector[2]
Electrostatic change with change in temp.of flake
Pyroelectric flake is cut from a single crystal
Ex ; Triglyceride sulphide

13. REFERENCES
1) Instrumental methods of chemical analysis , fifth revised and
enlarged edition by Gurdeep R. Chatwal, Sham K. Anand,
published by Himalaya Publishing House, Page no = 2.41-2.51
2) A text book of pharmaceutical analysis, Vol-2, by G.Vidya Sagar,
published by Kalyani Publishers, Page no = 313-325
3) Principles of instrumental analysis, Sixth edition, by Dougals A
Skoog, E James Holler, Stanley R. Crouch,published by Thomson
Higher Education, Page no = 438-452
4) Spectrometric identification of organic compounds, Seventh
Edition, by Robert M. Silverstein, Francis X. Webster, David J.
Kiemle, published by John Wiley and Sons ,Page no = 78-80