2. A spectrophotometer is an instrument for
measuring the transmittance or absorbance of a
sample as a function of the wavelength of
electromagnetic radiation.
3. The key components of spectrophotometer are-
Light Source
Wavelength selectors
Sample Cuvet
Detectors
Display Unit
4. • It must be stable
• It must be of sufficient intensity for the transmitted
energy to be detected at the end of the optional path.
•It must be supply continuous radiation over the entire
wavelength region in which it is used.
5. • Use in the region
350-2000nm.
• These measure most
effectively in the
visible region 320-
1100nm.
• Instruments that only
use tungsten lamp as a
light source will only
measure in the visible
region.
6. • Consist of two
electrode contain in
hydrogen filled
silica envelop.
•Gives continuous
spectrum in region
180-380nm.
• Above 380nm
emission is not
continuous.
7. • Measure in UV
region 190-370nm.
• Operate at high
temperature. Normal
glass housing can not
used for casing.
Instead, a fused
quartz, UV glass, or
magnesium fluoride is
used.
• Lamp life is
approximately
1000hrs.
8. • Use in region 200-
800nm.
• Life time is
approximately 500-
1500hrs.
•It consist of fused
quartz or other heat
resistant glass arc
tube, with a tungsten
metal electrode at
each end.
9. • Wavelength range
is 200-600nm.
• It is a gas discharge
lamp that uses an
electric arc through
vaporized mercury to
produce light.
• Mercury lamps are
more energy efficient
with luminous
efficacies of 35-65
lumens/watt.
11. • It permit certain bands of wavelength (bandwidth
of ~50nm)to pass through.
• The simplest kind of filter is absorption filters, the
most common of this type of filters is colored glass
filters.
DISADVANTAGE-
They are not very good wavelength selectors
because they allow the passage of broad
bandwidth and they absorb a significant fraction
of the desired radiation.
12.
13. The monochromator is used to disperse the
radiation according to the wavelength. The
essential elements of a monochromator are an
entrence slit, a dispersing element and an exit
slit.
The entrence slit sharply defines the
incoming beam of hetrochromatic radiation.
The dispersing element disperses the
hetrochromatic radiation into its component
wavelengths. The position of despersion device
is always adjust by rotating motor.
14. The exit slit allows the nominal wavelength
together with a band of wavelengths together with
a band of wavelengths on either side.
The dispersing element may be Prism of
Grating.
15. • Dispersion by prism depends on refraction of light
which is wavelength dependent.
• violet color with higher energy (shorter wavelength)
are diffracted or bent least.
•As a result, the polychromatic light is dispersed into
its individual color.
16.
17. • Polychromatic radiation from the entrance slit is
collimated (made into beam of parallel rays) by a
concave mirrors.
• These rays fall on a reflection grating, whereupon
different wavelengths are reflected at different angles.
• The orientation of the reflection grating directs only
one narrow band wavelengths to the exit slit of the
monochromator.
• Rotation of grating allows different wavelengths to
pass through the exit slit.
19. • For Visible and UV
spectroscopy, a liquid
sample is usually
contained in a cell
called a cuvette.
• Glass is suitable for
visible but not for UV
spectroscopy because
it absorbs UV
radiation. Quartz can
be used in UV as well
as in visible
spectroscopy.
20. • The detectors are devices that convert
radiant energy into electrical signal.
• A Detector should be sensitive, and has a
fast response over a considerable range of
wavelengths.
• In addition, the electrical signal produced
by the detector must be directly proportional
to the transmitted intensity (linear
response).
21. • It is also known as photo
voltai cell.
• It constitutes-
1- A steel support
plate.
2- Layer of metallic
selenium, which is few
hundredths of a millimeter in
thickness.
3- A thin transparent
electrically conductive layer,
applied by cathodic sputtering.
22. • Photo diodes
operates on
principle of p-n
junction diode.
• Its responsivity
is 250-500mA W-1
across the visible
spectrum.
23. • It is a very sensitive device in which electrons
emitted from the photosensitive cathode strike a
second surface called dynode which is positive
with respect to the original cathode.
• Electrons are thus accelerated and can knock out
more than one electrons from the dynode.
• If the above process is repeated several times, so
more than 106 electrons are finally collected for
each photon striking the first cathode.
25. • Single beam instruments are less expansive.
• High energy throughput due to non-splitting of source
beam results in high sensitivity of detection.
26. • Little or no lamp warm up time is required. This not
only improves throughput of results but also conserves
lamp life.
• Modern improvements in optics permit high level of
automation and offer the same or even better level of
detection.
27. Absorbance & Transmittance displayPower indicator light
Sample
holder
Wavelength
selector
Absorbance & Transmittance control
Power switch
Zero control
28. 1) Power on
2) Select wavelength
3) 0% Transmittance
adjustment(Calibration)
4) Blank (Reference cell) is
inserted into cell holder
5) 100% Transmittance
adjustment
6) Sample cell is placed in the
cell compartment
7) Readout absorbance
8) Power off
31. • Detection of impurities.
• Structure elucidation of organic compound.
•Quantitative analysis.
• Qualitative analysis.
• Dissociation constants of acids and bases.
• Chemical kinetics.
• Quantitative analysis of pharmaceutical substances.
• Molecular weight determination.
• As HPLC detector.
• Examination of polynuclear hydrocarbons.
32. www.molecularinfo.com/MTM/UV.pdf
Instrumental Methods of Chemical Analysis by Gurdeep
R. Chatwal and Sham K. Anand
Spectroscopy of Organic Compounds by P.S.KALSI
http://www.youtube.com/watch?v=pxC6F7bK8CU&feat
ure=player_detailpage
