Determination of residual glyphosate and aminomethylphosphonic acid in wheat flour and oats samples by non-derivatization method based on ultra-performance liquid chromatography-high resolution mass spectrometry

Abstract

A rapid and accurate analysis method based on ultra-performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) was developed for the determination of residual glyphosate (GLY) and aminomethylphosphonic acid (AMPA) in wheat flour and oats samples. The wheat flour and oats samples were firstly subjected to vortex and ultrasound extraction; then, the extract solution was purified by MCX solid-phase extraction (SPE) cartridges as well as protein precipitation using acetonitrile. The chromatographic separation was carried out on a Dikma Polyamino HILIC column (150 mm×2.0 mm, 5 μm) by linear gradient elution procedure using 5 mmol/L ammonium acetate in water (pH=10.5) and acetonitrile as the elution solvent. An electrospray ion source in negative mode and parallel reaction monitor (PRM) mode was used for quantification by the internal standard method. The instrument conditions for liquid chromatography (LC) and HRMS, and the sample pretreatment conditions for GLY and its metabolite AMPA were systematically optimized. In addition, the matrix effect and injection system residue were investigated, and a comparison of different analytical methods was carried out. The results indicated that GLY and AMPA showed good linearities in the range of 5.0-100.0 μg/L with coefficients (R2) higher than 0.999. The limits of detection (LODs) were found to be 0.005 and 0.05 mg/kg for GLY and AMPA, respectively. The recoveries of GLY and AMPA in the wheat flour and oats samples were in the range of 93.8%-115% and 89.8%-110% at the spiked levels of 0.1, 0.5, and 2.0 mg/kg, respectively, while the relative standard deviations (RSDs) were all less than 10%. The results of the matrix effect test revealed that the matrix inhibition effect could be reduced by using an isotopic internal standard with the matrix effect parameter |η|<3%. Moreover, the injection system residue was effectively controlled with a residual level of less than 1.0%. A comparison of the developed method with the reported derivatization method indicated little difference, with RSDs of 2.19% and 3.07% to the assigned value, respectively. The established analytical method was used for the Food Analysis Performance Assessment Scheme (FAPAS) proficiency test (No. 09122, GLY in oats), and the results were satisfactory with a z value of 0.2. Moreover, the result obtained using this method was very closed to the assigned value of the FAPAS QC sample, with a recovery of 102.2% (No. T09119QC, GLY in wheat flour). The proposed method is fast, simple, sensitive, and accurate, and it can be applied for the daily monitoring of GLY and its metabolite AMPA in wheat flour and oats samples.