Rapid Analysis of Phytic Acid by Paper Spray Mass Spectrometry

TL;DR

This paper introduces a fast and accurate method to measure phytic acid in food samples using a new mass spectrometry technique.

Contribution

A novel derivatization and paper spray mass spectrometry method for rapid phytic acid quantification without chromatography.

Findings

The method achieved good linearity (R² ≥ 0.9965) and low detection limits (LOD 0.08 μg/mL).

The technique showed high precision (<10% RSD) and recoveries between 87.2% and 122.4%.

The method was validated on rice bran samples, showing potential for food/plant matrix analysis.

Abstract

Phytic acid (PA), owing to its strong acidity and multidentate metal-chelating properties, readily forms multiple adduct/complex ions in mass spectrometry and is prone to pronounced matrix effects, resulting in complicated spectra and compromised sensitivity and quantitative robustness, which poses a major challenge for rapid and accurate PA quantification. Herein, we developed a rapid quantitative method for PA based on trimethylsilyldiazomethane (TMSD) methyl-ester derivatization coupled with paper spray mass spectrometry (PS–MS). PA was derivatized with TMSD to yield the methylated product (PA-Me), and the derivative solution was purified via “post-derivatization nitrogen blow-down followed by water reconstitution”, thereby markedly reducing background interference. In positive-ion mode, the stable sodium adduct ion [PA-Me+Na]+ (m/z 851.04) was used as the quantifier, enabling fast quantification with selected ion monitoring (SIM). PS–MS was performed with a 15 μL spotting volume and methanol/water (90/10, v/v, containing 0.1% formic acid) as the spray solvent, allowing rapid analysis without chromatographic separation. The method exhibited good linearity over 0.125–30 μg/mL (R2 ≥ 0.9965), with a limit of detection (LOD, S/N = 3) of 0.080 μg/mL and a limit of quantification (LOQ, S/N = 10) of 0.270 μg/mL. The intra-day and inter-day precision values were both < 10% (RSD), and recoveries ranged from 87.2% to 122.4%. This LC-free strategy features low solvent consumption and high analytical throughput, and was validated using rice bran protein and rice bran polysaccharide samples, providing technical support for rapid screening and quality control of PA in complex food/plant matrices.

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