Liquid Chromatography with Pulsed Amperometric Detection for Speciation of Mercury

Liquid chromatography with pulsed amperometric detection (PAD) at an Au electrode was successfully applied for speciation of mercury: inorganic mercury, methylmercury and ethylmercury. The optimized conditions for triple‐step potential waveforms utilized in PAD were: E1 1800 mV, t1 50 ms; E2 300 mV, t2 3850 ms; E3 750 mV, t3 100 ms; mercury oxidation was monitored at E3. With the eluent of HClO4 (0.10 M) + KCl (1.0 mM) + CH3CN (1.0%) at a flow rate 0.80 mL/min, three mercury species were fully separated in 6 min on a glass column (3 mm × 10 cm) packed with Chemcosorb C18 (5 μm). However, the first peak (inorganic mercury) was commonly overlapped by the solvent front. The relative standard deviations (n = 6) for methylmercury (15 ppb) and ethylmercury (30 ppb) were 4.2% and 2.8%, respectively. The linear range tested was 2 – 500 ppb (r = 0.9998) for methylmercury, and was 4 – 1000 ppb (r = 1.000) for ethylmercury. The detection limits (S/N = 3) were 1.2 ppb and 1.8 ppb for methylmercury and ethylmercury, respectively. The results of determination of the mercury‐containing species thimerosat in three commercial contact‐lens solutions agreed satisfactorily with the expected values.