ASSAY OF ASCORBIC PHOSPHATES AND INVITRO AVAILABILITY ASSAY OF ASCORBIC MONOPHOSPHATES AND POLYPHOSPHATES

A method was devised to assay ascorbic phosphate esters in biological materials by potassium bromoxide hydrolysis followed by determination of the liberated ascorbic acid. For the differential measurement of ascorbic acid and ascorbic phosphate, a spectrophotometric method was employed to screen out the interfering substances based on studies of absorbance curves of 2,4‐dinitrophenyl hydrazine derivatives. A variety of vertebrate tissues were examined for phosphatase activity on ascorbic phosphate esters. The results suggest that pigeon kidney, rat liver and several tissues of fishes readily hydrolyse ascorbic monophosphate but not ascorbic polyphosphate. Hydrolysis of ascorbic monophosphate is completed by both phosphatases of intestine, kidney and liver acting at neutral pH and phosphatase of stomach acting at acid pH. Thus, ascorbic monophosphate has the potential to be a source of available vitamin C in vivo, and this explains its antiscorbutic activity in scurvy‐prone animals. Copyright © 1990 John Wiley & Sons, Ltd