Samples are placed in cells for measurements. The figure above shows the ten available shapes of sample cells. Generally, the square cell with an optical path length of 10 mm is used. However, in cases where absorption is low, a cell with a longer optical path length is used, whereas when absorption is high, a cell with a shorter optical path length is used. The following describes the relationship between absorption strength (absorbance) and optical path length. This formula can be used to determine the appropriate optical path length.
Absorbance A = E•C•L
E: Absorption coefficient
C: Concentration of sample
L: Optical path length
A square cell with a stopper is generally used to measure volatile liquid samples, and a micro-cell is used to measure a sample with a small volume. Sample cells are made of the three materials given below. The wavelength range in which measurement is possible is fixed for each material as indicated:
Fused silica (S cells): 190 to 2500 nm
Glass (G cells): 320 to 2500 nm
Fused silica (IR cells): 220 to 3200 nm
|Square cell||Optical path length 10 mm||1|
|Optical path length 20 mm||6|
|Optical path length 50 mm||6|
|Optical path length 100 mm||6|
|Square cell with stopper||Optical path length 10 mm||2|
|Semi-micro cell||Optical path length 10 mm||3|
|Semi-micro black cell||Optical path length 10 mm||3'|
|Micro black cell||Optical path length 10 mm||8|
|Super-micro black cell||Optical path length 10 mm||7|
|Optical path length 5 mm||7'|
|Cylindrical cell||Optical path length 10 mm||
|Optical path length 20 mm|
|Optical path length 50 mm|
|Optical path length 100 mm|
|Short path cell||Optical path length 1 mm||
|Optical path length 2 mm|
|Optical path length 5 mm|
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