Frequently Asked Questions

Spectrophotometry

Question

How can I use Potassium Dichromate to verify the performance of my spectrophotometer?

Answer

 

 

The use of Potassium Dichromate solvated in dilute Perchloric acid is an established and well recognised method for the validation of the absorbance scale and linearity of a spectrophotometer in the UV region.

 


When prepared in 0.001M Perchloric acid, potassium dichromate gives a spectral scan containing characteristic peaks at 257 nm and 350 nm, and troughs at 235 nm and 313 nm. Within the concen­tration range 20-100 mg/l, if the absorbance scale of a narrow SBW (< 2 nm) spectro­photometer is linear, the apparent absorbance of a series of concentrations will be a linear function of concentration.

 

 

Reference kits that are used for testing the UV region of a Spectrophotometer, are supplied with a calibration certificate that indicates the absorbance of the peaks and the troughs. These values are for a specific bandwidth, typically 2nm, and are therefore valid only 

for spectrophotometers operating at that bandwidth. 

values that are obtained from an instrument with a bandwidth >2nm would be different to those indicated at 2nm.

 Thus,


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