Ultra-performance liquid chromatography of amino acids for the quality assessment of pearl powder.

Abstract

Pearls have been widely used as a traditional medicine, in cosmetics, and as a health food supplement in China since ancient times. However, the identification and quality assessment of pearl powder have been challenging tasks because of the similar morphological features and chemical composition of its common adulterants, especially conch powders. In this study, ultra-performance liquid chromatography was combined with pre-column derivatization to rapidly quantify 14 amino acids in pearl powder and its analogues. Based upon the quantification results, a quality criterion of a total amino acid content of not less than 1.10% was proposed for pearl powder. Principal component analysis indicated that leucine and phenylalanine were the amino acids characteristic for distinguishing between pearls and nacres. The area ratio of leucine to phenylalanine was demonstrated to be an effective diagnostic marker to discriminate freshwater cultured pearls, natural seawater pearls, and nacres. The proposed method, involving both the qualitative and quantitative aspects, was subsequently applied to quality assessment of pearl powders purchased commercially in various parts of China; eight out of 18 batches were deemed authentic and unadulterated. In the future, this analytical process should play a significant role in standardizing and providing quality control to the pearl powder market.