Determination of Heavy Metal Ions in Chinese Herbal Medicine by Microwave Digestion and RP-HPLC with UV-Vis Detection

Abstract.

A new method for the simultaneous determination of heavy metal ions in Chinese herbal medicine by microwave digestion and reversed-phase high-performance liquid chromatography (RP-HPLC) has been developed. The Chinese herbal medicine samples were digested by microwave digestion. Lead, cadmium, mercury, nickel, copper, zinc, and tin ions in the digested samples were pre-column derivatized with tetra-(4-chlorophenyl)-porphyrin (T₄-CPP) to form the colored chelates which were then enriched by solid phase extraction with C₁₈ cartridge and eluted from the cartridge with tetrahydrofuran (THF). The chelates were separated on a Waters Xterra ^™RP₁₈ column by gradient elution with methanol (containing 0.05 mol L⁻¹ pyrrolidine-acetic acid buffer salt, pH=10.0) and THF (containing 0.05 mol L⁻¹ pyrrolidine-acetic acid buffer salt, pH=10.0) as mobile phase at a flow rate of 0.5 mL min⁻¹ and detected with a photodiode array detector in the range of 350–600 nm. In the original samples the detection limits of lead, cadmium, mercury, nickel, copper, zinc and tin are 4 ng L⁻¹, 3 ng L⁻¹, 6 ng L⁻¹, 5 ng L⁻¹, 2 ng L⁻¹, 6 ng L⁻¹, and 4 ng L⁻¹, respectively. This method was applied to the determination of lead, cadmium, mercury, nickel, copper, zinc and tin in Chinese herbal medicine samples with good results.