Comparison of phytate and other organic P forms in Mehlich-3 and Alkaline-EDTA matrices by ICP, NMR and mass spectrometry

Authors: Elkin, Kyle; Bryant, Ray; Moore, Philip; CADE-MANUN, BARBARA - Agri Food - Canada

Submitted to: 5th International Phosphorus Workshop(IPW5)
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2016
Publication Date: 12/12/2016
Citation: Elkin, K.R., Bryant, R.B., Moore Jr, P.A., Cade-Manun, B. 2016. Comparison of phytate and other organic P forms in Mehlich-3 and Alkaline-EDTA matrices by ICP, NMR and mass spectrometry. Abstract Book. Organic Phosphorus Workshop. 5-9 September 2016. Windermere, UK. P.67.

Interpretive Summary: Phosphorus (P) is a leading cause of water quality degradation in many 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 our inability to characterize and quantify organic P forms. We compared several current analytical approaches for measuring organic P and developed a new approach using mass spectroscopy to characterize and quantify phytate, a commonly occurring organic P form found in manures and soils. 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.

Technical Abstract: 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 the organic P fraction, 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 tandom 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. Soils from the Delmarva Peninsula in Maryland, Northeastern Arkansas, Saskatchewan, and Prince Edward Island were analyzed for phytate and other organic P. Beyond the question of phytate concentration, the goal was to look at how pH and different cations (Al with respect to Alum treatment, and Ca with respect to general soils) stabilize phytate and its stereoisomers in soil. Furthermore, are other related organic P compounds affected by the same stabilizing processes, and how do these affect the ability of the extraction to reliably extract them. We will also show the distribution of phytate isomers (sycllo, neo, chiro) found naturally in soil and attempt to correlate these with a stabilizing factor such as cations. 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.