Accuracy and linearity of spectrophotometers in clinical chemistry laboratories.

Solutions of cobalt nitrate sealed in vials were circulated to all clinical chemistry laboratories in the United Kingdom. Participants reported wavelengths of maximum absorbance together with the actual absorbances obtained. The results were compared with values obtained from the National Physical Laboratory. The results show a wide scatter, and several instruments were extensively repaired or replaced as a result of the survey. The most recently marketed machines had the best performance, and it is suggested that regular quality control and maintenance of the machines is vital. It is intended to set up a scheme for regular monitoring of spectrophotometer performance.