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

• Establishing organic phosphorus (P) composition in soil will help P management.
• We quantified organic P and organic acids in NaOH extracts from ferralsol soils.
• Ion chromatography (IC) separated 11 anions in a single run.
• The variability of the quantification was less than 20% for most of the analytes.
• Recovery rate of organic P assayed by colorimetry and HPIC was about 100%.

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 (0.5 N) was validated as an extractant for both organic P and LMWOAs. A mixture of 200 mM 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 25 minute 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.