Interference of mercury(II) in the colorimetric determination of inorganic phosphate in water

Abstract

Mercury(II) caused a significant positive interference in the colorimetric determination of low levels of inorganic phosphate by the procedure of Murphy and Riley. The interference resulted from the formation of a precipitate that varied in particle size and was not always visible to the naked eye. With higher levels of inorganic phosphate a coarse precipitate formed that partially removed the molybdophosphate complex ion from solution. Elimination of mercury(II) interference was achieved by formation of a complex that resulted from the addition of chloride or a metabisulphite-thiosulphate reagent, as used in a conventional procedure for the removal of arsenate prior to the determination of inorganic phosphate.