Comparison of effectiveness of different ashing auxiliaries for determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method

Abstract

An improved method for the determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method is proposed. The recoveries of phosphorus (P) from selected inorganic and organic P-containing compound standards after ignition with different auxiliaries, such as MgSO 4, Mg(NO 3) 2, MgCl 2, Mg(Ac) 2 and CaCl 2, were compared. We found that the phosphorus from most compound standards could not be completely recovered when these compounds were ignited (450–500°C) with the MgSO 4 as auxiliary and the baked residue was extracted with 0.2 mol l −1 HCl for 30 min at 80°C or at room temperature. P recoveries, for example, were poor, less than 85%, if pyrophosphate and metaphosphate were ignited with the addition of MgSO 4 prior to the extraction of the baked residue with 0.2 mol l −1 HCl at 80°C for 30 min. In contrast, MgCl 2, Mg(Ac) 2 and CaCl 2, as well as Mg(NO 3) 2, could all yield complete P recoveries at routine ashing temperatures (450–500°C). The results demonstrate that MgCl 2 is a more effective auxiliary agent for the determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method than MgSO 4 which is commonly used.