Evaluation of a colorimetric method for vitamin A estimation.

A simple colorimetric procedure for plasma vitamin A is evaluated, which does not require sophisticated or expensive equipment. Vitamin A values obtained with 30 human plasma samples and 11 liver samples obtained from lactating rabbits, using a colorimetric procedure based on Carr-Price reaction with ferric chloride and acetyl chloride were compared with those obtained with spectrophotometric and spectrofluorimetric micro methods. With widely varying plasma samples, the values showed a high degree correlation and good agreement. The intraassay variation was 3% which is in the acceptable range. The plasma samples could be analysed within 4 weeks and the reagents, were found to be stable, unlike some batches of trifluoro acetic acid (TFA).