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An inductively coupled plasma mass spectrometer (ICP-MS) equipped with a dynamic reaction cell (DRC) was used for the determination of Ca and P in foodstuffs. In this study, two different reaction gases, CH4 and O2, were introduced successively through the different channels to alleviate different interferences in the same analysis run. The effect of the operating conditions of the DRC system was studied to get the best signal-to-noise ratio for each element. The interfering 40Ar+ at m/ z 40 was reduced in intensity by up to five orders of magnitude by using 1.0 mL min(-1) CH4 as reaction cell gas in the DRC. On the other hand, by using O2 as the reaction gas, 31P+ was converted to 31P16O+ that could be detected at m/z 47 where there was less interference. The limits of detection for Ca and P were 0.2 ng mL(-1) and 0.3 ng mL(-1), respectively. This method was used to determine the concentrations of Ca and P and the ratio of Ca to P in NIST SRM 1549 non-fat milk powder and NIST RM 8345 whole milk powder reference materials and an infant milk powder and an infant cereal-rice sample purchased locally. The results for the reference samples agreed satisfactorily with the reference values. The accuracy of the determination was better than 4.1 and 0.9% for Ca and P, respectively. The results for infant milk powder and infant cereal were also found to be in good agreement with the value on the bottle label. Precision (RSD) between sample replicates was better than 4.8% for all the determinations.

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.

Simultaneous determination of cysteine (RSH) and cystine (RSSR), two important sulfur-containing amino acids, in capillary electrophoresis (CE) has been an analytical task. Dual-microelectrode amperometric detection seems to be a good scheme, but significant difficulty in electrode construction and poor detection limit for RSSR determination remain major short-comings. In reverse pulse amperometric (RPA) detection, the applied potentials are repeatedly pulsed back and forth between the reducing initial potential (e.g., Ei =-1.4 V) and the oxidizing final potential (e.g., E r =0.0 V) at a single, gold-mercury amalgam (AuIHg) microelectrode. At E;, RSSR is reduced to RSH which Causes catalytical oxidation of the Au/Hg amalgam microelecuode when the potential is pulsed to E f • The resulting anodic current is then recorded. Therefore, by using RPA detection after CE separation, RSH and RSSR can be simultaneously determined.

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