| Objective: Vitamin C is a hydrophilic vitamin with higher concentration in plasma than other vitamins; however, its unstable chemical properties and strong polarity limit the accurate measurement of plasma concentration. The objective of the present study was to establish a quick, stable and accurate method for vitamin C measurement of large plasma samples. And to determine the plasma vitamin C concentrations of healthy subjects using the established method, to provide evidence of daily dietary intakes of vitamin C. And also, was to evaluate the bioequivalence of several vitamin C preparations by using this method.Methods: Precipitated the plasma proteins with metaphosphoric acid and extracted the vitamin C from plasma, then determined the vitamin C concentration by HPLC-UV with ODS as the solid phase. Using above method, the plasma concentrations (morning in the fasting state) of 128 male students with uncontrolled nutrition, as well as those of 14 students among them after 200 mg daily oral dose of vitamin C of 13 days (morning vitamin C prior to breakfast) were determined. Single oral doses of compound paracetamol and vitamin C in two preparations were given to 18 healthy volunteers. And their plasma concentrations of vitamin C were also evaluated.Results: Vitamin C was kept stable up to 12 hours in separated plasma after metaphosphoric acid treatment. The peak of vitamin C was separated well from the peaks of impurities on chromatography. It was found that vitamin C levels of the students with normal nutrition were (4.7 ± 2.7)μg·mL-1, which clustered near the lower limit of the normal range. After the multiple-dose of 200 mg daily, the steady-state plasma levels were significantly increased to (12.4 ± 1.9)μg·mL-1 (P<0.01), almost twice of the primary levels. The pharmacokinetic parameters of vitamin C for the test preparation (Compound tablets with 200 mg vitamin C) and... |
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