In this video we are
going to discuss about the ultraviolet
visible spectroscopy also known as UV
vis spectroscopy.
when the ultraviolet or visible light in the electromagnetic
spectrum
passes through a sample or gets
reflected from a sample its intensity
decreases the measurement of this
attenuated intensity is called the
ultraviolet and visible absorption
spectroscopy this type of spectroscopy is
useful for performing quantitative
measurements. qualitative measurements
however cannot be effectively done with
the help of UV visible spectroscopy the
basic principle of this absorption
spectroscopy is the beer Lambert's law
The concentration of analyte or sample
in a solution is determined by measuring
absorbance of EMR at different
wavelengths. UV visible spectroscopy
helps in characterizing the absorption
and transmission of different materials
like pigments coatings windows and
filters. The light source used is
generally a deuterium discharge lamp
for measurements in the ultraviolet
region and tunsten halogen lamp for
measurement in the visible region
depending on the type of instruments the
dispersing materials or dispersing body
used to isolate the wavelength of light
will be an absorption filter
interference filter a prism monochromator
or diffraction grating.
When measurement is done utmost care should be
taken to reject any stray light falling
on the detector assembly this stray
light can affect the measurement values
and induce errors in readings
the detectors used for measuring the
intensity of radiation can be a
photodiode, a phototube or a
photomultiplier tube also known as a PMT
the available UV visible absorption
spectrometers employ one of the
following design strategies. A single
light beam and sample holder is present
with the facility for selecting a fixed
wavelength for a range of EMR. A fixed
wavelength or scanning type spectrometer
the dual light beam and sample holders a
spectrometer with an array detector. here
the measurement of absorption for
different wavelengths is performed
simultaneously
the first instrument that
we will be studying is a photometer the
basic principle of operation of
photometer is the Beer Lambert's law a
photometer
or a colorimeter is employed to perform
quantitative analysis of a given analyte.
the sample is normally in the liquid
state the sample is placed in a test
tube, a cuvette which is kept in the
sample holder of the instrument
measurement using photometer
requires a standard reference sample
concentration for the standard reference
must be known the readings for the
standard are noted down as displayed
by the photometer then the unknown sample
i.e. the sample under test is placed
in the sample holder and the readings
for the same are noted down.
using the
readings of reference and those of the
sample under test the concentration of a
test sample is given as the test sample
concentration equals the concentration
of reference sample into a ratio of the
sample reading and reference sample
reading
in the next video
we will be talking about the single
beam photometer