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UV-VIS-NIR Spectroscopy
According to Beer-Lambert's law, the Absorbance(A) of a solution at a particular wavelength is given by A=∈bc, where c is the concentration of the compound, b is the path length of the cell and ∈ is the molar extinction coefficient. ∈ is characteristic of a particular compound at a given wavelength. This principle is used for quantitative measurements.
The block diagram of the double beam, double monochromatic ratio recording spectrophotometer instrument available at SAIF is shown below.
The spectrometer is well suited for taking UV-VIS-NIR spectra of samples in both dissolved(solution) form and in the solid state. The instrument can also be used to study single crystals, thin films and powder samples. The diffuse reflectance accessory is available for solid samples.
The UV cutoff(i.e.,the wavelength at which the solvent absorbance in a 1cm path length cell is equal to 1AU, using water in the reference cell) is given in Table I. The relationship between absorbance(A) and percent transmission(%T) is given in Table II.
Table.1 UV Cut off for Common Solvents
Solvent |
UV Cutoff(nm) |
Acetonitrile |
190 |
Water |
190 |
Hexane |
195 |
Cyclohexane |
200 |
Isopropyl Alcohol |
205 |
Methanol |
205 |
Ethyl Alcohol |
210 |
n-Propyl Alcohol |
210 |
Trifluoroacetic Acid |
210 |
Tetrahydrofuran |
212 |
n-Butyl Alcohol |
215 |
1,4-Dioxane |
215 |
Ethyl Ether |
215 |
Iso-Octane |
215 |
Isobutyl Alcohol |
220 |
Ethylene Dichloride |
228 |
Dichloromethane |
233 |
Chloroform |
245 |
N,N-Dimethylformamide |
268 |
Dimethyl Sulfoxide |
268 |
Toluene |
284 |
Chlorobenzene |
287 |
o-Xylene |
288 |
o-Dichlorobenzene |
295 |
Acetone |
330 |
Table II: Equivalent Absorbance(A) for a given percent transmittance value(%T)
%T |
A |
100 |
0 |
10 |
1.0 |
1.0 |
2.0 |
0.1 |
3.0 |
0.01 |
4.0 |
0.001 |
5.0 |
0.0001 |
6.0 |
0.00001 |
7.0 |
0.000001 |
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