Gas-diffusion flow injection determination of Hg(II) with chemiluminescence detection

A gas-diffusion flow injection method for the chemiluminescence detection of Hg(II) based on the luminol-H2O2 reaction was developed. The analytical procedure involved the injection of Hg(II) samples and standards into a 1.50 M H2SO4 carrier stream, which was subsequently merged with a reagent stream of 0.60% (w/v) SnCl2 in 1.50 M H2SO4 to reduce Hg(II) to metallic Hg. The gas-diffusion cell was thermostated at 85 °C to enhance the vaporisation of metallic Hg. Mercury vapour, transported across the Teflon membrane of the gas-diffusion cell into the acceptor stream containing 1.00 × 10−4 M KMnO4 in 0.30 M H2SO4, was oxidised back to Hg(II). The acceptor stream was merged with a reagent stream containing 2.50 M H2O2 in deionised water and then the combined stream was merged with another reagent stream containing 7.50 × 10−3 M luminol in 3.00 M NaOH at a confluence point opposite to the photomultiplier tube of the detection system. The chemiluminescence intensity of the luminol-H2O2 reaction was enhanced by the presence of Hg(II) in the acceptor stream. The corresponding increase was related to the original concentration of Hg(II) in the samples and standards. Under optimal conditions, the chemiluminescence gas-diffusion flow injection method was characterised by a linear calibration range between 1 μg L−1 and 100 μg L−1, a detection limit of 0.8 μg L−1 and a sampling rate of 12 samples per hour. It was successfully applied to the determination of mercury in seawater and river samples.