UV SPECTROSCOPY AND INSTRUMENTATION .INSTRUMENTAL METHODS OF ANALYSIS, B.PHARM 7TH SEM. AND FOR BSC,MSC CHEMISTRY. This is Geeta prasad kashyap (Asst. Professor), SVITS, Bilaspur (C.G) 495001

1. Presented by : Mr. G.P Kashyap ( Asst. Prof )
Siddhi Vinayaka Inst. of Technology & Sciences (Bilaspur,
C.G)

2.  The instrumentation techniques are a very important
and fascinating part of Chemical Analysis of different
substances like food materials, Drugs, body fluids, Air,
Environment factors, engine oils.
 Instrumentation techniques are performed to obtain
information's regarding the chemical compositions of
specific substance.

3.  ANALYTICAL TECHNIQUES: Techniques is a
fundamental scientific phenomenon that has proved for
providing information on the composition of sample.
 INSTRUMENTAL METHODS: Analysis of
composition of substances is example of instrumental
method.
 METHODS: is a specific application of a technique to
solve an analytical problem.
 PROCEDURE & PROTOCOL: A procedure is the
written instructions for carrying out a method.

4. On the basis of principle area:
1. SPECTROSCOPIC TECHNIQUES:
• UV & Visible spectrophotometery
• Infrared spectrophotometery
• Atomic spectrometery (Emission & Absorption)
• NMR
• ESR
• Raman spectroscopy
• Fluorescence spectroscopy

5. 2. Electrochemical Techniques:
• Potentiometry
• Voltametry
• Electrogravimetric techniques

6. 3.Chromatographic Techniques:
• Gas chromatography
•HPLC
•Ion Exchange chromatography
•HPTLC
•TLC
•Paper chromatography

7. 4. Hyphenated Techniques:
• GC-MS( gas chromatography-mass
spectroscopy)
•ICP-MS(inductively coupled plasma-mass
spectroscopy)
•GC-IR
•MS-MS

8.  Ultraviolet (UV)-visible spectroscopy is a type
of absorption spectroscopy in which UV-
visible light is absorbed by the molecule.
 Absorption of the UV-visible radiations
results in the excitation of the electrons from
lower to higher energy levels.

10. Light source:
❖It must be stable.
❖It must be have sufficient radiant energy over the
wavelength region where absorption is to be measured.
❖It should must be sufficient intensity for the transmit
energy.
❖The wavelength range of visible light lies b/w 4000 Ǻ
to 7500 Ǻ

11.  TUNGSTEN LAMP: It’s a lamp made up of tungsten
wire which is used in electric bulb.
 Used rarely now because of when the wavelength range
less then 350 nm then its problem of intensity
fluctuations.


12. HYDROGEN LAMP:
• Broad spectrum(3500Ǻ-1200Ǻ) , widely stable.
•Pair of electrodes is enclosed in glass tube filled with
hydrogen gas.

13. Deuterium discharge Lamp
➢A deuterium arc lamp (or simply deuterium lamp) is a low-
pressure gas discharge light source often used in spectroscopy.
when a continuous spectrum in the ultraviolet region is needed.
➢3-5 Times more intensity as compare to Hydrogen lamp/
more stable.

14. Xenon discharge Lamp
✓ The xenon arc lamp is also a popularlight sourcefor use in colour
measuringinstruments.
✓The xenon lamp contains two electrodesenclosedin a glass bulb
filledwith xenon gas.
✓High voltageis appliedto the electrodes (Tungsten), which
momentarilyreleasessparks to create light flash.

15.  A lamp that consists of vaporized mercury to generate
light by using an electric arc is known as a mercury
vapor lamp
 They are energy efficient (35 to 65 lumens/watts)
 The output is clear white light
 It provides with high intensity, its radiation line are not
broad its becomes very sharp.
 Not suitable for continuous spectral,

18.  Wavelength selectors limit the radiation
absorbed by a sample to a certain wavelength
or a narrow band of wavelengths.
 There are several types of wavelength
selectors. Here we will consider
 filters,
 grating monochromators,
 and prism monochromators.

19. Filters
Filters are wavelength selectors that allow
narrow bandwidths of radiation to pass
through. They can be divided into four main
categories:
➢ absorption filters
➢ cut-off filters
➢ interference filters
➢ and interference wedges.

20. Absorption filters
❑Absorption filters absorb most polychromatic radiation and
transmit only a specific band of wavelengths.
❑They are inexpensive and can be as simple as colored
glasses or plastics.
❑Only about 10-20% of the incident radiation is transmitted
through an absorption filter.

21. Cut-off filters
✓With cut-off filters, the transmission of
radiation is nearly 100%.
✓ However, this is only achieved for a specific
band of wavelengths and transmission rapidly
decreases to zero over the remainder of the
spectrum.
Spectrum of a specific cut-off filter

22.  Interference filters are sometimes called Fabry-
Perot filters and are dependent upon the concept
of wave interference.
 An interference filter is composed of a
transparent dielectric sandwiched between two
semitransparent metallic films and then two
glass plates to protect the filter.
 The thickness of the dielectric and the reflectivity
of the metallic films are carefully selected
because these factors control the transmitted
wavelengths. The transmitted radiation will have
a very narrow bandwidth.

24.  Grating monochromators are located within
compartments of some AAS instruments and
are responsible for producing narrow bands
of radiation. There are five components
found in most grating monochromators:
 an entrance slit
 a collimating lens or mirror
 a reflection grating
 a focusing element
 and an exit slit.

25. The change in the angle of reflection varies with
wavelength. In other words, polychromatic radiation will be
separated into its components because each wavelength of
radiation will be reflected by the grating at a different angle.
One of the major advantages of gratings is the uniform way
they disperse radiation linearly along the focal plane. The
figures below illustrate the linear dispersion in a grating
system
Uniform Linear Dispersion of Gratings

26. A reflection grating consists of a hard, polished, optically
flat surface containing many parallel and closely spaced
grooves that is covered with metal to increase
reflectivity. The groove density can be a low as 10 to as
high as 6000 grooves/mm. Typically, a grating for the
ultraviolet and visible region has approximately 300 to
2,000 grooves/mm while a grating for the infrared
region has approximately 10 to 200 grooves/mm.
Close-up view of grooves in a grating

28. ❑ Prisms refract light at the surface of two interfaces
creating angular dispersion, and can be used to
disperse ultraviolet, visible, and infrared radiation.
❑ An advantage of using prisms is their wide
spectrums that can be obtained despite their low
dispersion. However, prisms use a non-linear
dispersion method. This makes it difficult for
focusing a desired wavelength through the exit slit.
The wavelength and dispersion have an inverse
relationship, where shorter wavelengths cause
increased dispersion.

30.  Cuvettes
 The containers for the sample and reference
solution must be transparent to the radiation
which will pass through them.
 Quartz or fused silica cuvettes are required for
spectroscopy in the UV region.
 These cells are also transparent in the visible
region.
 Silicate glasses can be used for the manufacture
of cuvettes for use between 350 and 2000 nm.

31.  The photomultiplier tube
 is a commonly used detector in UV-Vis
spectroscopy. It consists of a photoemissive
cathode (a cathode which emits electrons when
struck by photons of radiation),
several dynodes (which emit several electrons for
each electron striking them) and an anode.
 A photon of radiation entering
 the tube strikes the cathode, causing the
emission of several electrons. These electrons are
accelerated towards the first dynode (which is
90V more positive than the cathode).

32. •The electrons strike the first dynode, causing the emission
of several electrons for each incident electron.
•These electrons are then accelerated towards the second
dynode, to produce more electrons which are accelerated
towards dynode three and so on.
• Eventually, the electrons are collected at the anode.
•By this time, each original photon has produced 106 -
107 electrons. The resulting current is amplified and
measured.
•Photomultipliers are very sensitive to UV and visible
radiation.
•They have fast response times. Intense light damages
photomultipliers; they are limited to measuring low power
radiation.

35.  Phototubes are photodetectors that feature
high sensitivity, superior temperature
stability, wide dynamic range, large
photosensitive area, and low-voltage
operation.
 They are widely utilized in applications such
as chemical and medical analysis and laser
measurement.

36. A phototube (or photoelectric cell), invented by Julius
Elster and Hans Geitel in 1893, is a photoemissive
detector based on a small glass tube containing
electrodes where the external photoelectric
effect (or photoemissive effect) is utilized.
Such tubes are often evacuated or sometimes filled with a
gas under low pressure.
Phototubes operate according to the photoelectric effect:
Incoming photons strike a photocathode, knocking electrons out
of its surface, which are attracted to an anode. Thus current is
dependent on the frequency and intensity of incoming photons.
Unlike photomultiplier tubes, no amplification takes place, so
the current through the device is typically of the order of a
few microamperes.

37. A caesium-antimony cathode gives a device that is very
sensitive in the violet to ultra-violet region with sensitivity
falling off to blindness to red light.
Caesium on oxidised silver gives a cathode that is most
sensitive to infra-red to red light, falling off towards blue,
where the sensitivity is low but not zero.

39.  Nowadays, phototubes are largely replaced
with solid-state devices like photodiodes,
where the internal photoelectric effect is
used.
 For some applications, however, phototubes
can still have substantial advantages:

40. substantial advantages:
•They can have a lower dark current, leading to a lower noise
equivalent power.
•They can be made with a large photosensitive area while still
having a high detection bandwidth.
•The high dynamic range and high stability of phototubes can
be advantageous for precise measurements, e.g.
in spectrometers.
•Particularly for UV applications, the high stability (comparing
with semiconductor devices, for example)