Abstract: In the manifold illustrated, the water sample is mixed with a K2Cr2O7/H2SO4/ HgSO4/Ag2SO4 reagent prep. described and a 10^-240 µL portion is injected into a stream of water, which carries it through a microwave oven. The residual Cr(VI) is retained on an anion-exchange resin column and subsequently eluted for determination by flame AAS. COD values of 25-5000 mg/l can be measured, and the detection limit is ~7 mg/l. Fifty determinations can be performed per h. There is no matrix effect.

Abstract: Three micronebulizers, the high-efficiency nebulizer (HEN), the microconcentric nebulizer (MCN) and the micromist (MM), were compared with a conventional pneumatic concentric nebulizer working at low liquid flow rates in ICP-AES. The gas back-pressure, the free liquid aspiration rate, the drop size distribution of primary and tertiary aerosols, the solvent and analyte transport rates, the emission intensity and the limits of detection were measured. The solvent evaporation inside the spray chamber proved to be a very important transport phenomenon when working at very low liquid flow rates. The micronebulizers produced finer primary aerosols, higher solution transport rates through the spray chamber and higher sensitivities than the conventional pneumatic concentric nebulizer. The HEN used in this work provided slightly lower ICP-AES limits of detection than the other two micronebulizers, but at the expense of a higher back-pressure.

Abstract: In the present work, a new flow injection analysis (FIA) manifold for the rapid determination of COD is presented and evaluated. The FIA manifold combines sample digestion by means of an oxidant solution (i.e., potassium dichromate and mercury sulfate) and an acid solution (sulfuric acid and silver sulfate) in a domestic microwave oven with the liquid-liquid extraction of Cr(VI) with tri-Bu phosphate (TBP). Finally, the remaining (non-reduced) Cr(VI) is determined in the organic phase by atomic absorption spectrometry. The digestion of the organic matter is carried out in the stopped-flow mode. Potassium hydrogenphthalate has been used for optimization of the method and as a standard to check its performance. The optimized conditions (oxidation) are: digestion time, 7 min; acid concentration, 67% (v/v). The optimized conditions for the extraction of the remaining Cr(VI) are: acid concentration, ≥30% (v/v); TBP, 1 mL. The proposed method has been successfully applied, with the exception of pyridine, to several organic compounds and waters. A semi-micro method has been used for comparison. The application range extends from 40 to 12,000 mg O2/L, whereas the lowest limits of detection and quantification are 13.5 and 45 mg O2/L, respectively. Following this method, the interference of Cl- can be compensated for at least up to 10,000 mg L-1 Cl-. Up to nine samples per h can be analyzed.