[Colorimetric determination of plasma vitamin C: comparison between 2,4-dinitrophenylhydrazine and phosphotungstic acid methods (author's transl)].

The evaluation of a recently published colorimetric method for plasma ascorbic acid determination, using phosphotungstic acid (PTA), was performed by comparison with the largely employed 2,4-dinitrophenylhydrazine (DNPH) procedure. The method has been evaluated according to International Federation of Clinical Chemistry (I.F.C.C.) recommendations. In particular, calibration procedures have been performed and precision, accuracy, linearity, specificity and sensitivity have been studied in biological samples. Linear regression analysis indicates that the two methods do not correlate completely. The PTA method shows a better recovery. The PTA method shares with the DNPH procedure a poor precision at low concentrations of vitamin C in plasma such as to make results less reliable at the clinically significative levels.