Two-dimensional ion chromatography tandem-mass spectrometric (2D-IC-MS/MS) method for the analysis of phosphorus compounds in soil

Investigations into soil organic phosphorus (P_o) dynamics are instrumental in understanding the transformations and processes responsible for ecosystem productivity. However, quantitative analysis of P_o in a soil environment is extremely challenging due to low target analyte concentrations and matrix interferences with chromatography and analysis. Consequently, a two-dimensional ion chromatography-tandem mass spectrometric (2D-IC-MS/MS) method was developed to estimate soil P_o concentrations. The first dimension diverted early eluting anions to waste while preconcentrating P compounds in a trap column, followed by chromatographic separation and detection in the second dimension. Detection was done using a mass spectrometer, and quantification was performed using the multiple reaction monitoring scan (MRM) method. The linear range of the studied P compounds, mostly nucleotides, was 0.05-50 ng/mL. Most P compounds were detected and quantified in calcareous subsoil samples in the concentration ranges 0.70-51.78 ng/g. The developed method achieved chromatographic separation that allowed unambiguous identification of isobars/isomers and isotopologues contributing to interferences in MS detection. However, improvements to the extraction method and post-clean-up procedures are required due to the complexity of soil extract composition, extreme matrix effect and/or loss of analyte during preconcentration. The method is ideal for simultaneously analyzing P compounds from environmental samples to elucidate key components of the soil P dynamics.