A rapid indirect titrimetric determination of microgram amounts of orthophosphate

Abstract

Microgram amounts (10 to 50 µg) of phosphorus as orthophosphate have been determined in a sample volume of 1 to 4 ml, by addition of excess of thorium nitrate solution and micro titration of the excess of thorium with standard EDTA solution. Filtration of the solution before titration is not required. The presence of large excesses of chloride, bromide, iodide, nitrate, sulphate, perchlorate and silicate can be tolerated, but fluoride, borate and arsenate interfere. Microgram amounts of orthophosphate have been determined in synthetic sample solutions containing other anions. Any one result is accurate to within ±1 µg of phosphorus.