Determination of phosphorus in the presence of iron(III) and iron(II)

Abstract

Both manual and automated techniques have been developed for the determination of phosphorus in the presence of iron(III). Interference from iron(III) has been substantially eliminated by its reduction with hydroxyl-ammonium chloride prior to the formation of the molybdophosphate blue complex using ascorbic acid. The small but reproducible error due to the formation of iron(II) is dependent on the iron to phosphorus ratio present in the digest solution but is significant only when this ratio is more than 500.

Both methods have been applied successfully to the determination of phosphorus in digests and extracts of soil materials where the ratio is far below the value of 500, thus making a correction unnecessary.