Determination of chloride in surface and groundwater by centrifugal analysis
A procedure has been developed for the determination of chloride in environmental samples using a Cobas Fara centrifugal analyser. The procedure is based on the spectrophotometric hexacyanoferrate(III) method. Analytical variables are manipulated with ease using this instrument, thus simplifying the task of choosing reagents and reagent concentrations. Of the two commonly used iron(III) donators, iron(III) nitrate was found to be more sensitive than ammonium iron(III) sulphate, and the calibration graph for iron(III) nitrate was more linear. Assessed by comparison with reference mineral samples from the US EPA, and by results obtained using a Technicon AAII continuous flow analyser, the results obtained using the Cobas Fara procedure were found to be both accurate and precise. The following equation describes the relationship developed when surface water and groundwater samples containing chloride are analysed using the Cobas Fara and the Technicon AAII analysers: y= 0.994x+ 0.089; r2= 1.0; n= 79. It is concluded that the Cobas Fara procedure produces high quality results with a considerable time (300 samples h–1) and sample-size (80 µl) saving.