COMPARISON OF SAMPLE PREPARATION METHODS FOR THE SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHORUS IN SOIL AND COAL FLY-ASH

Three different sample preparations were evaluated for determining phosphorus spectrophotometrically in two different matrices, soil and coal fly ash. The absorbance of the blue molybdenum complex was measured at a wavelength of 804 nm with a 1 cm cell on a spectrophotometer. One digestion method involved an HCl leaching and the other two methods involved a lithium metaborate fusion to which was added an additional HF digestion step in the third digestion method. The HCl leaching method is not recommended for either matrix. The faster lithium metaborate fusion method is recommended for soils and fly ash.