High-performance liquid chromatographic determination of selenocysteine with the fluorescent reagent, N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid

The method described is based on derivatization of selenocysteine with N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonic acid and responds linearly to selenocysteine spiked into plasma. Recovery is insensitive to inter-individual variation or use of serum versus plasma, but is decreased by hemolysis. The derivative is stable for at least three days. The total imprecision of determinations in plasma was 0.8–2.1% (coefficient of variation) over the range of 6–30 μM selenocysteine, with a detection limit of 0.4 μM (3 × S.D.). There was no significant interference from plasma thiols. This appears to be the first report of the selective reaction of free selenocysteine with a fluorescent reagent. This simple method works well in plasma and serum and may be adaptable to other types of samples.