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Naked-Eye Chemical Colorimetry for the Rapid Determination of Copper(Ⅱ), Cadmium(Ⅱ) and Lead(Ⅱ) in Chinese Crude Drugs

Limei L, Yan L, Yi C, Xi P, Bohou X, Zhimin Z, Yamei L, Ping W and Duanfang L

A naked-eye chemical colorimetry method was developed for the rapid determination of Cu2+, Cd2+ and Pb2+ ions in Chinese crude drugs. Determinations of Cu2+, Cd2+ and Pb2+ were performed using copper reagentï¼Ã‚ˆDDTC, diethyl dithiocarbamateï¼Ã‚‰, cadion (P-nitrophenyl diazonium amino azobenzene) and xylenol orange, respectively, as colorimetric reagents. At pH 6, an orange-red or purple-red complex compound was obtained with the reaction between Pb2+ and xylenol orange; the reaction was linear with the concentration of Pb2+ in the range of 0.2~10.0 mg.L-1, and the detection limit was 0.2 mg.L-1. At pH 10, an orange-red complex compound was obtained with the reaction between Cd2+ and cadion; the reaction was linear with the concentration of Cd2+ in the range of 0.1 ~ 5.0 mg.L-1, and the detection limit was 0.1 mg.L-1. At pH 10, a brown-yellow complex compound was obtained with the reaction between Cu2+ and DDTC; the reaction was linear with the concentration of Cu2+ in the range of 0.5 ~ 10.0 mg.L-1, and the detection limit was 0.5 mg.L-1. The detection limits of Cu2+ and Pb2+ meet the Chinese Pharmacopoeia limit standards for copper and lead levels in Chinese crude drugs, but the detection limit of Cd2+ did not meet the standard, indicating that there is a certain gap compared with the Chinese Pharmacopoeia guideline. In addition, the method was successfully applied to detect trace amounts of Pb2+, Cd2+, and Cu2+ ions in eight types of Chinese crude drugs (a total of 80 batches) with satisfactory results. The tested drugs were Paeoniae radix alba, Glycyrrhizae radix et Rhizoma, Astragalus membranaceus, Salviae miltiorrhizae radix et rhizom, Panacis quinque folii radix, Crataegi fructus and Lonicerae japonicae flos. The results were compared with those using the traditional atomic absorption spectroscopy (AAS) method and showed good agreement.