Flow injection on-line sorption preconcentration and separation in a knotted reactor (KR) was coupled to cold vapor atomic fluorescence spectrometry for the determination of trace mercury in mineral water. Mercury was preconcentrated by on-line formation of mercury diethyldithiocarbamate complex (Hg-DDTC) and absorption of the resulting neutral complex on the inner walls of a knotted reactor. A 20%(V/V) HNO3 solution heated by electromagnetic induction heating technique was used as eluent to remove the absorbed Hg-DDTC from the KR, and then the vapor mercury generated by mixing the resulting solution and KBH4 was determined on-line by cold vapor atomic fluorescence spectrometry. The 20% HNO3 was employed as both the efficient eluent and the required acidic medium for subsequent mercury vapor generation in our work. Using 20% HNO3 instead of conventional organic solvent as eluent, the proposed method is simple, easy operational and environmentally friendly. Under the optimal experimental conditions, the sample throughput was approximatively 30/h with an enhancement factor of 35. The detection limit of mercury was 2.0 ng/L. The precision(RSD, n=11) was 2.2% at the 0.1 μg/L Hg2+ level.

The preparation of electrophoretic microcolumn and its application to the electrophoretic separation of amino acids with a 2-mm I.D. fused-silica microcolumn packed with uniform quartz microncrystal prepared by hydrothermal synthesis are reported. With 1.5 mmol/L disodium phosphate buffer solution (pH 11.5) containing 30% (V/V) methanol, the tryptophan, phenylalanine and tyrosine were separated by the microcolumn electrophoresis and detected by an UV spectrophotometer without derivatization. The limits of detection were 0.038, 0.21 and 0.20 mol/L, respectively. The separation efficiency of tryptophan was 4.4×104 plates/m. The sample capacity of the electrophoretic microcolumn achieved 35 μL. The precisions of the microcolumn electrophoresis were satisfactory. The thermal effects of the electrophoretic microcolumn that without packing, packed with 360 μm quartz sand and with 9 μm length quartz microncrystal were discussed, respectively. It was found that the electrophoretic microcolumn packed with quartz microncrystal was able to inhibit Joule heat, increase sample capacity and enhance detection sensitivity. The microcolumn electrophoresis is one of the high-performance separation techniques for an in-situ, real-time and portable electrokinetic flow analysis system.