Determination of trace lead, cadmium and mercury by on-line column enrichment followed by RP-HPLC as metal-tetra-(4-bromophenyl)-porphyrin chelates

This paper reports the utilization of tetra-(4-bromophenyl)-porphyrin (T4BPP) as a chelating reagent using Waters Xterra™ RP18 column for the on-line column enrichment and the separation of trace lead, cadmium and mercury ions by reversed-phase high-performance liquid chromatography (RP-HPLC) with photodiode array detector. When the Hg–T4BPP, Pb–T4BPP and Cd–T4BPP chelates were injected into the injector and sent to the enrichment column with 0.05 mol l−1 of pH 10.0 pyrrolidine–phosphoric acid buffer solution (containing 10% of tetrahydrofuran (THF)) as mobile phase. The chelates were retained on the top of the enrichment column. After the enrichment is finished, by switching the valve of six-ports switching valve, the retained metal–T4BPP chelates will be eluted by mobile phase in reverse direction and will travel towards analytical column. With THF (containing 0.05 mol l−1, pH 10.0 pyrrolidine–phosphoric acid buffer salt) and 0.05 mol l−1, pH 10.0 pyrrolidine–phosphoric acid buffer solution (containinging 10% THF) gradient elution as mobile phase, the chelates separation on the analytical column was satisfactory. The linearity ranges are 0.01–120 μg l−1 for each metal ion. The detection limits (S/N=3) of lead, cadmium and mercury are 1.0, 0.5 and 1.0 ng l−1, respectively. This method can be applied to the determination (μg l−1) level of lead, cadmium and mercury in drinking water with satisfactory results.