Calibrationless flow-through stripping coulometric determination of arsenic (III) and total arsenic in contaminated water samples after microwave assisted reduction of arsenic(V).

A simple and rapid procedure for the calibrationless determination of trace concentrations of As(III) and total As in contaminated water samples is presented. Arsenic is preconcentrated as As(III) in a flow-through cell with a gold plated porous electrode and is then stripped anodically by a constant current. The stripping chronopotentiogram is registered and evaluated. The As concentration is calculated directly from the combined Faraday's laws. The total As content was determined after converting all As species to As(III) by microwave-assisted reduction with hydrazine hydrochloride in a closed vessel. The detection limit was found to be 0.15 microg/L and the linear response range was 0.5 to 10,000 microg/L. Tap water, surface water, and waste water samples were analyzed.

Calibrationless determination of mercury by flow-through stripping coulometry.

Trace concentrations of Hg were determined in a flow-system by constant current stripping chronopotentiometry in coulometric mode. Mercury was electrodeposited from the flowing sample solution in an electrochemical flow-through cell on a large surface porous electrode plated with a thin layer of gold. The deposited mercury was then stripped with constant current and the potential change of the working electrode was recorded and evaluated. Since complete electrochemical yields were achieved at both the deposition and dissolution steps, the mercury concentration in the sample solution could be calculated from Faraday's law. The detection limit and reproducibility of the method were about 0.1 ng/ml for 10 ml sample solution and 4%, respectively. The time for a complete analysis was 2 to 5 min. The utility of the method was demonstrated with the analysis of reference materials, water samples, waste materials, plants and charcoal catalysts.

Preconcentration of Cr(III) and total Cr in waters for flame AAS in a flow-through electrochemical/sorption cell.

Chromium in water samples is determined by flame atomic absorption spectrometry (AAS) after the preconcentration of Cr(III) species on activated alumina at pH 7 in a flow system coupled on-line to the AAS instrument. The total Cr concentration is determined after the electrochemical reduction of chromate ions to Cr(III) which are preconcentrated together with the original Cr(III) species in the sample. Both the reduction and the sorption are carried out in a combined cell containing a porous electrode, a layer of the sorbent and the counter electrode in series. The porous electrode is made of glassy carbon particles coated with gold. Tap, river and synthetic sea water samples were analyzed with this method. The detection limits are 0.5 ng/ml and 250 ng/ml for 500 ml and 1 ml sample solution, respectively.