2. SPECTRPHOTOMETRY
• A method in which the absorption or transmission
properties of a material is quantitatively measured as a
function of wavelength.
• The basic principle behind this method is that : “Each
compound absorbs or transmits light over a certain range
of wavelength”.
• A spectrophotometer is an instrument that measures the
amount of photons absorbed by a sample after it is passed
through its solution.
• With the spectrophotometer , the amount of a known
chemical substance can be determined by measuring the
absorbance.
3.
4. • Spectrophotometer can be classified into two different types :
• SINGLE BEAM SPECTRMETER :
• To measure the intensity of the incident light the sample must
be removed so that the reference can be placed each time.
This type of spectrometer is usually less expensive and less
complicated.
5. • DOUBLE BEAM SPECTOMETER
• In this type, before it reaches the sample, the light source is
split into two separate beams. From these one passes
through the sample and second one is used for reference.
This gives an advantage because the reference reading and
sample reading can take place at the same time.
6. Based on the wavelength of light used it can be classified into :
1) VISIBLE SPECTROMETER
• Uses visible range (400 – 700nm) of electromagnetic
radiation spectrum.
• Visible spectrophotometers vary in accuracy. Plastic and
glass cuvettes can be used for visible light spectroscopy.
2) UV SPECTOMETER
• Uses light over the UV range (180 - 400 nm).
• UV spectroscopy is used for fluids, and even solids.
Cuvettes, only made of quartz, are used for placing the
samples.
3) IR SPECTROPHOTOMETER
• Uses light over infra red range (700 -15000) of
electromagnetic radiation spectra.
7. DEVICE AND MECHANISM
• The spectrophotometer, in general, consists of two devices.
They are the following :
• 1. SPECTROMETER :
• A device that produce, typically disperse and measure the
light.
• 2. PHOTOMETER :
• Indicates the photoelectric detector that measures the light.
8. • The spectrometer consists of the following parts :
• 1. Light source: it produce a desired range of
wavelength of light.
• 2. Collimator: transmits a straight beam of light.
• 3. Monochromator: split the light into its
component wavelength.
• 4. Wavelength selector: transmits only the desired
wavelength.
9. • The photometer detects the light
absorbed by the sample as the light
from the slit is passed through the
solution. And then it sends signal to
the galvanometer or digital display.
11. 1) Light Source
• to provide a sufficient of light which is suitable for
marking a measurement.
• Tungsten Lamp
• Hydrogen Lamp
• Xenon Lamp
12. I) Tungsten Lamp
• It is the most common light source used in spectrophotometer
wavelength
• range of about 330 to 900 nm
• It has long life about 1200h.
13. II) Hydrogen / Deuterium Lamps
• For the ultraviolet region, hydrogen or deuterium lamps
are frequently used.
• their range is approximately 200 to 450 nm.
• Deuterium lamps are generally more stable and has long
life about 500h.This lamp generates continuous or
discontinuous spectral.
14. III) Xenon flash lamps
• Xenon flash lamps have several advantages as the
• following :
• 1)Their range between ( 190nm - 1000 nm)
• 2) Emit both UV and visible wavelengths
• 3) Long life
• 4) Do not heat up the instrument
• 5) Reduce warm up time
15. 2) Dispersion devices
• Dispersion devices
• Dispersion devices causes a different wavelength of light to
be dispersion at different angles.
• Types of Dispersion devices used are
A. Prism
B. Filters
A. Prism
• Prism is used to isolate different wavelength
• Prism may be made of glass or quartz.
16. B. Filters
• Filters separate different parts of the electromagnetic
spectrum by absorbing or reflecting certain wavelengths and
transmitting other wavelengths.
• Absorption filters are glass substrates containing absorbing
species that absorb certain wavelength. A typical example is
a cut on color filter, which blocks short wavelength light, and
transmits longer wavelength.
17. 3) Focusing devices
• Combinations of lenses, slits, and mirrors. Variable slits also
permit adjustments in the total radiant energy reaching the
detector.
18. 4) Absorption cells(Cuvettes)
• A cuvette is a kind of cell (usually a small square tube)
sealed at one end, made of Plastic, glass or optical grade
quartz and designed to hold samples for spectroscopic
experiments.
19. 5) Detectors
• Any photosensitive device can be used as a detector of
radiant energy .The photocell and phototube are the
simplest photodetectors, producing current proportional
to the intensity of the light striking them.
20. 6) Display devices
• The data from a detector are displayed by a readout device,
such as an analog meter, a light beam reflected on a scale,
or a digital display , Or liquid crystal display(LCD) .The
output can also be transmitted to a computer.
21. Uses of spectrometer
1) Measure the concentration of the solution:
• A spectrophotometer optically determines the absorbance or
transmission of characteristic wavelengths of radiant energy (light)
by a chemical species in solution. Each molecule absorbs light at
certain wavelengths in a unique spectral pattern because of the
number and arrangement of its characteristic functional groups,
such as double bonds between carbon atoms.
2) Identify organic compounds by determining the absorption
maximum:
• Spectrophotometers are used to identify organic compounds by
determining the absorption maxima (which for most compounds
and groups of compounds have very distinct fingerprints (that's
what the absorption curves and peaks are called).
22. 3) Used for color determination within the
spectral range
• If one is working in the range of 380 to 700
nm, the spectrophotometers can also be used
for color determination within this spectral
range.
