ON THE PHOSPHATE DETERMINATION IN GROUNDWATER

Contrary to surface water, groundwater is mainly anoxic and contains high iron(II) concentrations. Consequently, results of ortho-phosphate analyses often show a systematical underestimation since phosphate is coprecipitated or adsorbed by precipitating iron(III) hydroxide. This process is caused by aeration during sampling, storing and filtration of groundwater samples. The error of P-analyses can only be reduced by sampling and filtrating under inert gas and by an immediate addition of the chemicals for the molybdenum blue method. Storage of unfiltered, acidified samples is possible, too.