For the determination of vitamin C a precipitation step, which removes high molecular substances is performed first. After centrifugation the supernatant is injected into the HPLC system. The isocratic separation via HPLC at 30°C uses a ``reversed phase'' column. One run lasts 12 minutes. The chromatograms are recorded by a UV-detector. The quantification is performed by the delivered plasma calibrator; the concentration is calculated via integration of the peak areas, resp. peak heights. Sample Types: lithium heparinate plasma. Time: 10 minutes ? Vitamin C is a strong reducing agent. The oxidation of vitamin C leads to dehydroascorbic acid via a radicalic intermediate, in vivo. The three forms constitute a reversible redox-system. The most important function of ascorbic acid is the catalization in the biosynthesis of collagen. It is important for the de novo synthesis of bone, cartilage and teeth and wound healing. Vitamin C is needed for the synthesis of noradrenalin. Vitamin C plays an important role as antioxidant. It protects other molecules and cell structures from free radicals and reactive oxygen species. Ascorbic acid promotes the resorption of iron in the intestine and reduces the production of nitrosamines which might be carcinogenic.