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 organic phosphorus 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 minutes 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, polyphosphates, and nucleic acids. We refer to this new method as the eXtra high temperature dry combustion ash/hydrol method (X-HTDC) and recommend its application for measuring particulate phosphorus from organic compounds in aquatic systems.
In order to assess the intracellular phosphorus in microalgae, we recommend an oxalate reagent (Tovar-Sanchez 2003) to wash the microalgae collected on the filter to remove surface adsorbed phosphorus.