Determination of amino acids in the foods by reversed-phase high-performance liquid chromatography with a new precolumn derivative, butylthiocarbamyl amino acid, compared to the conventional phenylthiocarbamyl derivatives and ion-exchange chromatography.

A new derivatizing reagent, butylisothiocyanate (BITC), reacts quantitatively with the 22 standard amino acids and the amino acids in the acid hydrolysate of food and the protein standard, bovine serum albumin (BSA), at 40 degrees C for 30 min to yield butylthiocarbamyl (BTC) amino acids. The sensitivity of BTC-amino acid was similar to phenylthiocarbamyl (PTC) amino acid. The detection limit in both derivatives was about 3.9 pmol at 0.05 AUFS that showed a stable baseline for the quantitative determination. Analysis of the results obtained with BSA and food samples as BTC derivatives showed good agreement with those determined as PTC derivatives, ion-exchange chromatography and data presented in the literatures, except for a few amino acids. Especially the values compared to those of ion-exchange chromatography were very close, except for histidine. The advantage of the BITC reagent over the phenylisothiocyanate was that it had high volatility, so the excess reagent and by-products were removed in about 10 min, compared to about 1 h in the PITC reagent, with a common aspirator. In the BTC derivatives, cystine and cysteine were determined separately but in the PTC derivatives they were resolved into a single peak.