User Guide

For an introduction to the application and use of Certified Reference Materials in absorption spectrophotometry


This Reference Material can be used to qualify the absorbance scale and absorbance linearity, in the ultraviolet and visible regions of the spectrum (from 235 nm to 430nm) of spectrophotometers with spectral bandwidths of 2 nm or less. It is accepted for this purpose by most Pharmacopoeias and Standardisation Bodies, including:

European Pharmacopoeia
Deutsches Arzneibuch (German Pharmacopoeia)
United States Pharmacopeia
American Society for Testing and Materials
Therapeutic Goods Administration (Australia)
British Pharmacopoeia

Description and Discussion

Potassium dichromate in 0.001 M perchloric acid, permanently sealed by heat fusion into 10 mm UV-quality quartz cells. Solutions are prepared from solid potassium dichromate, NIST SRM 935a.

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 0.001 M 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

Typical spectra


Within the concentration range 0 - 240 mg/l, if the absorbance scale of the spectrophotometer is linear, the measured absorbances of a series of potassium dichromate concentrations will be a linear function of concentration. 12 solutions are available covering this concentration range in 20 mg/l steps.


When prepared at a 600 mg/l concentration, a potassium dichromate solution in 0.001 M perchloric acid can be certified at 430 nm for absorbance value.

Typical absorbance values at the certified wavelengths for the different concentrations are:


  Nominal Absorbance Values at Certified Wavelengths
Concentration 235 nm 257 nm 313 nm 350 nm 430 nm
20 mg/l  0.246 0.286 0.096 0.214  
40 mg/l  0.493 0.574 0.193 0.428  
60 mg/l  0.743 0.865 0.290 0.643  
80 mg/l  0.994 1.157 0.387 0.858  
100 mg/l  1.247 1.452 0.484 1.074  
120 mg/l  1.501 1.749 0.582 1.29  
140 mg/l  1.758 2.050 0.679 1.506  
160 mg/l  2.016 2.351 0.777 1.723  
180 mg/l  2.275 2.655  0.875 1.94  
200 mg/l  2.536 2.960  0.974 2.157  
220mg/l  2.790 3.256  1.071 2.373  
240 mg/l  3.043 3.552  1.168 2.589  
600 mg/l         0.954

Note: The above values are for guidance only, as measured values will be spectral bandwidth dependent. The Calibration Certificate accompanying each Starna Potassium Dichromate Reference gives actual values measured at a bandwidth of 1.0 nm, and only the certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths and bandwidth values. To meet pharmacopoeia instrumental resolution requirements, the instrument to be qualified should have a spectral bandwidth of 1.6 nm or less..


Catalogue Number

Catalogue Identity: RM-nn where nn indicates the concentration of the solution. For example, RM-02 is 20 mg/l, RM-04 is 40 mg/l, and so on up to RM-60, which is 600 mg/l. References can be ordered separately or in any combination simply by combining these numbers: for example RM-0204060810 would be a set comprising 20,40,60,80 and 100 mg/l references. For convenience, four sets covering different absorbance ranges are available. These are:

  Catalogue  Number

Potassium Dichromate Linearity Set, 0.09 to 1.5A
20, 40, 60, 80 & 100 mg/L & Blank Cell


As above, with additional 600mg/l reference for European Pharmacopoeia compliance


Potassium Dichromate Linearity Set, 1.5 to 3.5A
120, 140, 160, 180 & 220 & 240mg/l & Blank Cell 


Potassium Dichromate Linearity Set, 0.19 to 3.5A
40, 80, 120, 160, 200 & 240 mg/l & Blank Cell 



All individual references and sets are supplied with a perchloric acid blank cell.
Description: Starna Potassium Dichromate reference cells.