Using Waters’ latest tandem quadrupole technology, the Xevo TQ-XS, the sensitivity and repeatability was investigated for the simplified analysis of underivatized polar pesticides. A mixed mode, weak ion exchange/reverse phase analytical column allowed for MS friendly mobile phase of 50 mM aqueous ammonium formate (pH 2.9) to be readily used in electrospray negative ion mode.³
Waters Xevo TQ-XS, coupled with the ACQUITY UPLC System achieves sub parts per billion detection limits for glyphosate, glufosinate and aminomethylphosphonic acid (AMPA), as shown in Figure 1. Here an example of the chromatography obtained from the analysis of the three analytes of interest is shown at 0.002 mg/L in water, while inset shows the limit of quantitation achieved for each analyte based on signal-to-noise (S/N) ≥10.
System robustness, in terms of precision was observed from the analysis of a selection of spiked extracts of cereal-based foods and beverage. Extracts were prepared using a simple aqueous extraction, pass through SPE, spiked at 0.025 mg/kg, filtered and injected into the ACQUITY UPLC System coupled to Xevo TQ-XS. A summary of the results, run over almost 17 hours, and acquired from replicate injections in a single batch, is provided in Table 1, while an example of the chromatography achieved for each analyte in lentils is shown in Figure 2.
Linearity was evaluated for all analytes, in solvent and matrix. Excellent linearity was achieved using calibration curves bracketing the analytical run. An example is shown in Figure 3, where two curves are overlaid showing an R²≥0.995 with residuals <15% for all concentration levels (0.0005 to 1 mg/kg). When comparing the slopes of the solvent and matrix matched calibration curves, significant matrix effects (namely ion suppression) were observed, especially for AMPA, which could be mitigated by the use of stable isotope analogue internal standards.
