Abstract: Boiler water is analyzed with use of a T1-721 type flow injection analyzer (diagram given). Silicates in the sample react with 100 µL of 10% ammonium molybdate in a carrier stream of 3% H2SO4 in presence of 8% oxalic acid to suppress interference from PO43-, and with 10% ascorbic acid solution at 30°C; the molybdosilicate blue formed is detected at 780 nm. Recoveries were 99.7 to 100.5% with a coefficient of variation of 1%. From 50 to 6000 ppb of silicate could be determined, with an analysis time of 60 samples h-1.

Abstract: The toxic effects of mercury are well-known. To establish sources of mercury contamination and to evaluate levels of mercury pollution, sensitive, selective, and accurate analytical methods with excellent reproducibility are required. We have developed a novel methodology for the determination of trace mercury in environmental and foods samples by online coupling of flow injection (FI) displacement sorption pre-concentration in a knotted reactor (KR) to electrothermal atomic absorption spectrometry (ETAAS). The developed methodology involved the online formation of copper pyrrolidine dithiocarbamate (Cu-PDC), presorption of the resulting Cu-PDC onto the inner walls of the KR, and selective retention of the analyte Hg(II) onto the inner walls of the KR through online displacement reaction between Hg(II) and the presorbed Cu-PDC. The retained analyte was subsequently eluted by 50 µL of ethanol and online detected by ETAAS. Interferences from coexisting heavy metal ions with lower stability of their APDC complexes relative to Cu-PDC were minimized without the need of any masking reagents. The tolerable concentrations of Cu(II), Cd(II), Fe(III), Ni(II), and Zn(II) were up to 12, 20, 16, 20, and 60 mg L-1, respectively. No additional chemical modifiers for the stabilization of mercury were required in the present system owing to the stability of Hg-PDC at the drying stage, and no pyrolysis stage was necessary due to the effective removal of the matrices. With consumption of 2.5 mL of sample solution, an enhancement factor of 91 was obtained in comparison with direct injection of 50 µL of aqueous solution. The relative detection limit (3s) was 6.2 ng L-1, corresponding to an absolute detection limit of 15.5 pg. The precision (RSD, n = 13) was 1.1% at the 2 µg L-1 level. The method was successfully applied to the determination of mercury in several certified environmental and foods reference materials and locally collected water samples.