The use of nicotinic acid solvated in dilute hydrochloric acid is a well documented method for the validation of the absorbance scale and linearity of a spectrophotometer in the Far UV region. When prepared in 0.1M hydrochloric acid, nicotinic acid gives a spectral scan containing characteristic peaks at approx. 210nm and 260nm. Within the concentration range 5-25 mg/l, if the absorbance scale of a narrow SBW (2 nm) spectrophotometer is linear, the apparent absorbances of a series of concentrations will be a linear function of concentration, at a specified SBW.

The filled cells are tested and certified against the calculated values. A certificate is provided with each set of cells which has the certified absorbance values for each cell and the confidence limit. The certificate supplied is suitable for use with inspecting agencies when used in the context of a standard operating procedure for the quality control that is established in your laboratory. Each set is supplied with a sealed blank cell that was used for the certified measurment.

Measure the absorbance of the nicotinic acid cells at the two certified wavelengths. These wavelengths are: 213 and 261nm. The absorbance scale is verified by assuring that the absorbance readings on your instrument are within your instruments tolerance to the readings on the certificate supplied with the reference set. To evaluate linearity, plot a graph of concentration against absorbance for each of the four wavelengths.

Compare the absorbance values from your instrument with the expected values on the certificate supplied with the reference set. If the readings are within the expected range for your instrument then your absorbance scale is correct. If not, consult your service techincian and have the instrument evaluated

Each time that the analysis is repeated you can compare the new results with the previous results to check for any deviation. If your instrument needs service because of a change in absorbance scale accuracy, the historical data will greatly assist the service technician.