A novel and indirect method for L-cysteine detection in traditional Chinese medicines by chemical vapor generation-atomic fluorescence spectrometry

Abstract

L-Cysteine (L-Cys) is one of the material bases for the sweet taste of traditional Chinese medicines (TCMs), as well as the material basis for the pharmacological activity of TCMs in the treatment of diseases. Therefore, the rapid and accurate determination of the concentration of L-Cys has a certain significance for the quality evaluation of TCMs. In this work, a simple method was developed for label-free and indirect detection of L-Cys by chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS) based on the phenomenon that L-Cys can inhibit the CVG of arsenic ion (As(III)). Therefore, the AFS signal is inversely proportional to the concentration of L-Cys. The effects of the concentration of hydrochloric acid (HCl) and potassium borohydride (KBH4) in the CVG process and the reaction time between L-Cys and As(III) have been investigated. Under the optimal experimental conditions, it shows a good linearity in the concentration range of 2–18 mM. The limit of detection (LOD) of the presented method is 2.8 μM, with a relative standard deviation (RSD) of 0.5%. The method has been successfully applied in the analysis of L-Cys in several animal TCMs with good recoveries.