Rapid extraction of arsenic species from traditional Chinese herbal by dual-frequency ultrasound-assisted enzymatic digestion prior to spectral analysis

Abstract

Considering the huge difference of biological toxicity, it is extremely significant to recognize the exact content of arsenic species in actual samples. In this paper, a novel pretreatment technique for the efficient extraction of arsenic species from herbal samples is developed by dual-frequency ultrasound-assisted enzymatic digestion (DUED). The preservation of arsenic original form, reduction of the actual analysis time, environmental friendliness and free-interference in subsequent detection make this method over the traditional method such as wet digestion, ashing and some solvent extraction technologies. The combination of DUED and atomic fluorescence spectrometry realize the speciation analysis of arsenic in traditional Chinese medicine. The optimizations of experimental parameters have been achieved, and the potential mechanism is discussed. The experimental data showed that cellulase is suitable for the digestion of herbal matrix than α-amylase and papain. Ultrasound can significantly increase the rate of enzymatic hydrolysis of biological molecules, especially under dual-frequency ultrasound irradiation. The highest relative extraction efficiency can be obtained by combining 40 kHz ultrasonic bath (UB) with 20 kHz ultrasonic probe (UP). Two certified reference materials [CRMs, GBW(E)090066 and GBW(E)090067] and four practical herbs were used to evaluate the accuracy and practicability of the method. Inorganic arsenic, including trivalent arsenic and pentavalent arsenic, was the main species in the four herbal samples.

Keywords: Arsenic species; Cellulase; Dual-frequency ultrasound-assisted enzymatic digestion; Herbal matrix; Liquid chromatography-atomic fluorescence spectrometry.