Degradation of dehydroascorbic acid in parenteral nutrition mixtures

The degradation of ascorbic acid (AA) stored in parenteral nutrition (PN) r egimens is initially by oxidation, catalysed by trace elements, in particul ar copper. After prolonged storage the concentration of AA remains relative ly constant, with little variation, due to the lack of available oxygen. Th e initial degradation product is dehydroascorbic acid (DHAA). This is gener ated in an anaerobic environment, and is hypothesised to degrade by hydroly sis. It is the purpose of this investigation to ascertain the effect of tem perature and trace elements on the anaerobic degradation of DHAA, and to id entify the kinetics of the reaction. A stability-indicating reversed-phase HPLC assay was used. The column contained C,, reverse-phase packing (Luna), mean diameter 5 mum. The column dimensions were 15 cm long with an interna l diameter of 0.4 cm. The mobile phase consisted of methanol: phosphate buf fer (pH 7.8: 0.067 mol dm(-3)) at a ratio of 40: 60 (v/v) and also included Cetrimide (mixed alkyltrimethylammonium bromide) (0.05 mol dm(-3)) as an i on pair reagent. The flow rate was 0.7 ml min(-1) and detection was by ultr a-violet light absorption at 278 nm. This assay was used to monitor the deg radation rate of DHAA in PN mixtures with and without trace elements over a range of temperatures (5-35 degreesC). Results indicated a first order rea ction that was temperature-dependent but trace elements independent. (C) 20 01 Elsevier Science B.V. All rights reserved.