Comparison of Methods for the Determination of Total Phosphorus in Waters Containing Particulate Material

Perchloric acid digestion compared favorably with Na 2 CO 3 fusion for the determination of total P in a range of waters containing varying concentrations of both P and particulate material. The recovery of particulate P by persulfate digestion tended to decrease with increasing particulate material concentration in both natural unfiltered samples and in filtered samples to which particulate material was added. Recovery of added soil particulate P by persulfate digestion also decreased with increasing particle size. Low recovery of P by persulfate digestion was caused by the incomplete extraction of P occluded within oxides and hydrous oxides of iron. Between 58 and 86% of the P not recovered by persulfate digestion was in the inorganic form. Persulfate digestion is not recommended for the determination of total P in waters containing particulate inorganic materials of soil origin. Perchloric acid digestion is considered to be a more suitable method for such samples.