Quantification of Arginine in Dietary Supplement Tablets and Capsules by Silica Gel High-performance Thin-layer Chromatography with Visible Mode Densitometry

A quantitative method using silica gel HPTLC plates, automated band-wise sample application, detection with ninhydrin chromogenic reagent solution, and automated visible mode densitometry has been developed for determination of L-arginine hydrochloride in nutrition supplements containing a variety of other active and inactive ingredients. Accuracy was validated by analysis of spiked blank and standard addition samples and precision by performing replicate analyses on a single day and on different days. Recoveries from spiked blank and standard addition samples were 98.8% and 98.5%, respectively. Repeatability for two samples, each of which was analyzed six times on a single plate, was 1.92% and 0.674% relative standard deviation (RSD). The intermediate precision was 1.72% RSD for a sample analyzed in duplicate once per plate on four different days over a seven-day period. A survey was made of arginine content compared with label values for four commercial supplement products, using the new method. The method was shown to be suitable for routine analysis of nutritional supplements in a manufacturing quality-control or regulatory agency laboratory.