Analyses of vitamin C in biological samples with an emphasis on recent chromatographic techniques

AA analyses are rife with problems - but primarily stability of the sample AA and specificity are the most prevalent shortcomings of the assays reviewed. Should one desire to quantify AA alone with no consideration for DHAA or DKG, chromatographic separations such as those described by Nahrwold (1981) with reductants added to samples and standards using UV detection, or Iwata et al. (1985) with fluorescence or Tsao and Salimi (1982) with EC detection would probably be appropriate depending upon the equipment available. The initial preparation of sample must be tested to ensure that no spontaneous oxidation of AA occurs during the sample preparation. The main advantage of these chromatographic assays is simply that one is measuring AA directly. On the other hand, manual assays such as that proposed by Zannoni et al. (1974) or Samyn (1983) have apparently demonstrated sufficient specificity and sensitivity to be used as well. When other vitamin C compounds need to be quantified, chromatographic assays should be considered but the selection is largely dependant on the sample size (and thus sensitivity required), the possible interfering compounds, and the detector available. Ideally HPLC should ensure the specificity by resolving the compounds of interest from artifacts. However, the optical characteristics of DHAA and DKG which are quite different from that of AA and detection limitations have fostered a number of complicated manipulations to quantify the former.