Persulfate chemical wet oxidation method for the determination of particulate phosphorus in comparison with a high‐temperature dry combustion method

Abstract

A persulfate chemical wet oxidation (CWO) method for the determination of particulate phosphorus (PP) was improved and then compared with a conventional high‐temperature dry combustion (HTDC) method. In the improved CWO method, the concentration of the digestion reagent, potassium persulfate, was increased from 0.5% to 3% (w/v); the method exhibited high recoveries of P from various test materials under commonly used autoclave conditions (at 120°C for 30 min). The recoveries of P relative to those of the HTDC method were 102 ± 6.7% from standard organic and inorganic P compounds, and 100 ± 3.8% from natural particulate matter analogues including riverine suspended particulate matter (SPM), sediments, plankton, and geochemical reference materials of rock. However, low recoveries of 14% to 69% were observed for reference samples of clay minerals. Comparison using many samples of estuarine and pelagic SPM showed that the CWO method produced PP values consistent with those obtained by the HTDC method, except for some estuarine samples enriched in inorganic matter. The low recoveries were ascribed to the presence of an inorganic P fraction highly recalcitrant to chemical digestion. The procedural blank was lower for the CWO method than for the HTDC method. The filter blanks showed large variation among the filter materials tested; aluminum oxide membrane filters were shown to contain a considerable amount of P that could cause significant contamination in both methods. Analytical precision was equivalent between the two methods. Considering its simplicity and its less time‐consuming nature, the CWO method presented here is suitable for PP determination in aquatic environments.