Comparison of liquid chromatographic method to AOAC microbiological method for determination of L-tryptophan in tablets and capsules.
A reversed-phase liquid chromatographic (LC) method coupled with precolumn derivatization of L-tryptophan with phenylisothiocyanate was compared to the AOAC microbiological method for determining L-tryptophan in tablets and capsules. For the microbiological method, the concentrations of L-tryptophan were 4-8% lower in autoclaved test samples (hot method) than in test samples that were not autoclaved (cold method). When L-tryptophan values obtained by the LC method were compared to those obtained by the cold microbiological method, no significant differences were observed (P > 0.05). The mean relative standard deviations were 2.9% for the LC method and 1.6% for the cold microbiological method. The mean recoveries of standard L-tryptophan added before analysis were 99% for the LC method and 101% for the cold microbiological method. These results demonstrate that both methods are reliable for determining free L-tryptophan contained in tablets and capsules. However, the LC method has the advantages of using a smaller test portion and having a shorter analysis time.
Kim
H S
HS
U.S. Food and Drug Administration, Division of Nutrition, Washington, DC 20204.
Angyal
G
G
D002214:Capsules; D002626:Chemistry, Pharmaceutical; D002853:Chromatography, Liquid; D008828:Microbiological Techniques; D013607:Tablets; D014364:Tryptophan / Q000032:analysis*
D002214:Capsules; D013607:Tablets; D014364:Tryptophan