Quantification of organic P and low-molecular-weight organic acids in ferralsol soil extracts by ion chromatography

A better understanding of the composition of organic phosphorus (organic P) and low-molecular-weight organic acids (LMWOAs) in soil will make it possible to predict phosphorus cycling, improve biomass production and help phosphorus management in forest plantations. The method for quantifying organic P and LMWOAs in soil extracts was developed using ion chromatography (IC). Sodium hydroxide (0.5N) was validated as an extractant for both organic P and LMWOAs. A mixture of 200mM NaOH and ultrapure water was used to create a linear gradient elution. The eluent program separated five different organic P forms (glucose-6-phosphate, AMP, fructose-1,6-bisphosphate, ATP and phytate) as well as pyrophosphate from inorganic P (Pi), and four LMWOAs (malate, malonate, oxalate and citrate) in a 25minute run through an AS11 column. The variability of the quantification was expressed as the relative standard deviation which was less than 20% for most of the analytes. The recovery rate of organic P assayed by IC to colorimetry was 110±20%. This chromatographic method was shown to be suitable for the quantification of organic P and LMWOAs in soil samples and could be an easier alternative to 31P Nuclear Magnetic Resonance (NMR) measurement.