Improving quantification of particulate phosphorus

Abstract

Total particulate phosphorus (TPP) is often determined using the high-temperature dry combustion (HTDC) method followed by hydrolysis of the ash and then molybdenum colorimetry. Here, we show that a higher than traditionally used combustion temperature, 800°C vs. 450–550°C, improves phosphorus recovery from several phosphorus standard compounds, marine phytoplankton cultures, and particulate samples from the field. The ashing auxiliary MgSO4 further improves P recovery by improving decomposition, reducing volatilization during combustion, and increasing the efficiency of hydrolysis. A 0.2 M HCl hydrolysis, under 90°C for 30 min yields a higher P recovery compared with hydrolysis at room temperature or 60°C. In aggregate, these improvements to the method double the P recovery from phospholipids to 97%. TPP recovery from laboratory phytoplankton cultures and field samples increased an average of 11%, primarily due to the improvements in P recovery from phospholipids, polyphosphate, and nucleic acids. We refer to this new method as the eXtra high temperature dry combustion (X-HTDC) Ash/Hydrol method and recommend its application for measuring particulate phosphorus from organic compounds in aquatic systems.