420 triple airshot7/6/2023 ![]() Results and Discussion LC–MS/MS Method Performanceīecause of the high sample processing load of routine testing facilities, several method development decisions were made to meet their high sample throughput requirements. 2.7 μm Quasar SPP C18 column (PerkinElmer, Inc.) was used. For both LC methods, a 100 mm x 4.6 mm i.d. In total, 690 MRM transitions were monitored for 345 compounds in the ESI method, and 100 MRM transitions were monitored for 50 compounds in the APCI method, along with the internal standards (shown in Figure 2). A time-managed multiple reaction monitoring (TM-MRM) method was built for both APCI and ESI compounds. Instrumental parameters for both the APCI and ESI methods are shown in Table I. Absolute matrix effects in the additional tea matrices of chamomile, herbal blend, and catnip were determined by comparing the peak areas between the post-extract spike and solvent-only standards at 10 ng/mL and 100 ng/mL, expressed as %SSE (12). ![]() Matrix effects were determined by comparing the slopes between calibration curves made in neat solvent and tea extract (with stock standards spiked into solvent and extract), which was reported as a percentage of signal suppression and enhancement (%SSE). For analytes with accuracy values outside the range of 70–120%, LOQs were determined as the lowest point in the calibration curve with a S/N of greater than 10. Limits of quantification (LOQs) were reported at the lowest concentration level, which met the accuracy qualifiers within 70–120%, a relative standard deviation (RSD) of <20%, and the signal-to-noise (S/N) ratio of greater than 10 (for the quantifier transition) requirements. The accuracy and precision of the method were determined at the 10 ng/g and 100 ng/g level (spiked in tea samples) across four sample replicates. Solvent calibrants with stable isotope-labeled internal standards were used for calibration, with nine calibration standards prepared in a neat solvent spanning the range of 0.1–250 ng/mL. Excellent method performance (defined as an accuracy of 70–120% and a precision of 3 × 103 RCF, with 1 mL of the extract filtered through a 0.2 μm filter into a 2 mL amber vial for LC–MS/MS analysis. In this work, a simple solvent extraction approach was coupled with dual source electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) modes on an LC–tandem mass spectrometry (MS/MS) instrument to analyze 395 analytes extracted from black tea (345 compounds via ESI and 50 compounds via APCI, along with the internal standards). Multi-instrument approaches are often relied upon to analyze all pesticide targets, with the workload split between liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS) instrumentation. As regulatory laboratories search for and implement consolidated methods for multiple matrix and analyte classes, compound lists increase to hundreds or thousands of targets.
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