Fast and Selective Assay of l-Ascorbic Acid in Rose Hips by RP-HPLC Coupled with Electrochemical and/or Spectrophotometric Detection

Abstract

A simple, fast, and selective method for the assay of l-ascorbic acid in rose hips was developed using RP-HPLC. Ascorbic acid was extracted with 2% metaphosphoric acid and sample clean-up was optimized with C18 disposal extraction cartridges. Use of 0.5% metaphosphoric acid as the mobile phase completely suppressed the dissociation of ascorbic acid. Sufficient retention was achieved so that the addition of ion-pairing agents was not necessary. The column effluent was monitored by spectrophotometric (242 nm) and electrochemical detectors (550 mV vs Ag/AgCl); the electrochemical detector was found to be both more selective and more sensitive. By coup-ling the two detectors in series, a true two channel detection with on-line validation was achieved.

Reproducible results (r.s.d. 1-4%) were obtained from assays of several commercially available products, as well as from fresh rose hips, and revealed considerable differences in ascorbic acid content, ranging from 0.03 to 1.3%.