Comparison of Phytate in Various Soil Extraction Matrices By ICP, NMR, Chromatography and (HRAM) Mass Spectrometry.

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 in cases of limited sample can restrict 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, Calcuim Chloride, Bray-1, Olsen, and Acid Oxalate) 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.