[Current status of analytical methods for measuring provitamin A]

The difficulties inherent to provitamin A determination and the present state of development of the analytical methodologies are appraised. The procedures, the advantages and disadvantages and the possible sources of error of the methods involved are discussed. Open-column methods are still the most viable option in developing countries but the efficiency and reproducibility of the chromatographic separation depend largely on the analysts skill and experience. Although HPLC chromatograms are highly reproducible, the problem is to transform the peak areas to provitamin A concentrations because of the instability, varying purity and unavailability of provitamin standards. Internal standardization with the stable Sudan appears to be a promising solution. Separation of cis-isomers requires rechromatography in open-column systems. For HPLC, this problem still remains to be solved. Confirmation of the identity of the provitamins and prevention of degradation during the analysis are also dealt with. Notwithstanding the obstacles involved, reliable data can be obtained with adequate application of the analytical techniques and proper interpretation of the results.