Determination of vitamin E in microsamples of serum by liquid chromatography with electrochemical detection

In this procedure for determination of vitamin E by "high-performance" liquid chromatography with electrochemical detection, 25-microL serum specimens are deproteinized with ethanol. Vitamin E (alpha-tocopherol), its derivatives (beta- and gamma-tocopherols), and the internal standard (delta-tocopherol) are extracted into heptane and the extract is evaporated and the residue reconstituted with methanol before injection into the chromatograph. Within- and between-run CVs for an alpha-tocopherol concentration of 13.6 mg/L were 5.1% (n = 28) and 6.0% (n = 5), respectively. The standard curve is linear to 100 mg/L; the minimum concentration detectable is 0.1 mg/L. Analytical recovery ranged from 99.8% to 104.8%. In 36 specimens collected from apparently healthy subjects who were not taking vitamin supplements, alpha-tocopherol as determined by this method ranged from 4.3 to 9.7 mg/L, from 1.8 to 3.9 mg/L for beta- and gamma-tocopherols. Results by this method (y) and an HPLC-ultraviolet method (x) correlate reasonably (r = 0.81): y = 0.88x - 0.55 mg/L (n = 45). This procedure is adaptable to automated analysis, and the small sample requirement facilitates its applicability to neonates.