Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/18/2016
Publication Date: 10/13/2016
Citation: Elkin, K.R., Bryant, R.B., Kleinman, P.J., Moore Jr, P.A., Cade-Menun, B. 2016. Comparison of matrix effects on phytate analysis in Mehlich-3 and Alkaline-EDTA extracts by ICP, NMR, Chromatography and (HRAM) Mass Spectrometry.. ASA-CSSA-SSSA Annual Meeting Abstracts. Poster 441-732.
Interpretive Summary: The favored method of organic P identification over the last few decades has been 31P NMR. While this technique has the distinct advantage of speciating organic P, it has a relatively poor detection threshold (0.05 mg/ml), which typically limits 31P NMR to qualitative or confirmative applications. Additionally, ICP and colorimetry have been used in tandem as an indirect determination of organic-P by way of subtracting the colorimetric inorganic fraction from the determination of total P by ICP. Amongst these methods, there are also a number of chromatographic techniques that have been reported, however typical detectors (UV or conductivity) have been relatively unsuccessful at quantifying phytate. More recently, the increasing availability of high-resolution, accurate mass spectrometers has made the selective quantitation (single µg/l or lower) of many organic P species possible. Together, these techniques give a reliable overview of what properties are contributing to organic P processes in soils. Several extracts (Mehlich-3, NaOH-EDTA, and Mehlich-3 followed by NaOH-EDTA) were chosen to test on a variety of soils from various areas, which have a range of total P concentrations and different land uses. Phytate concentration, matrix pH effects and several phytate-cation interactions were investigated. While different extracts show different P forms (especially different levels of phytate), it also shows that organic P is not extracted from these different soils equally. This definitely suggests that care needs to be used when interpreting extraction analyses with ICP.
Technical Abstract: Phosphorus (P) is a leading cause of water quality degradation in impaired fresh water systems. Although substantial progress has been made in understanding the fate and transport of P from nonpoint agricultural sources based on measures of total P and orthophosphate-P, a comprehensive understanding of P dynamics is hampered by the complexity of P chemistry, most notably organic P. We compared several current analytical approaches to examine how the sample preparation procedure affected the quantitation of organic P. Furthermore, we were able to characterize forms of phytate in soils that have been stabilized to some degree by reaction with various cations. Improved analytical tools for characterizing organic P forms will lead to a better understanding of the complex interactions between P and soils that affect P losses in runoff and leachate and subsequent environmental impacts on water quality.