CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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chemical species. Since a particular peak height is proportional to concentration of the
species, one can use the technique for both quantitative and qualitative evaluation of a
chemical species [2.1-2.3]. UV-Vis absorption spectra were collected using Biomate model
UV-visible spectrophotometer with a range of 200-1100nm and resolution of 1nm.
As mentioned earlier the technique exploits the excitation of a chemical species using light.
Obviously a particular molecule absorbs in a range of wavelength around absorption
maxima. Not only intrinsic but also extrinsic factors govern peak position and broadening for
e.g. solvent properties.
The system consists of a calibrated source where incident light of a particular
wavelength is known. Now if a chemical species absorbs around λ max , then intensity of
transmitted light at that wavelength decreases. Decrease in intensity of transmitted light is a
function of concentration and path length (length of passage through the sample).Below
given equation gives relationship between the absorbance and different factors
I
Alog 10
I
0
cl
(2.1)
In above equation A is the absorbance, I0
is incident intensity I is transmitted intensity for a
particular wavelength and l is path length, is molar absorptivity constant and c is
concentration of that species. We assume that decrease in intensity arises from absorption of
light by sample and not scattering. Scattering is especially large in cases where solubility of
sample is poor. Additionally concentration of samples are expected to be kept low as at
higher concentration factors like intermolecular interactions and changes in refractive index
affect measurement. The scan over entire UV-Vis region gives rise to absorption spectra
which forms the basis of this technique.