Analysis of pesticides in soy milk combining solid-phase extraction and capillary electrophoresis-mass spectrometry

In this work, the determination of a group of triazolopyrimidine sulfoanilide herbicides (cloransulam‐methyl, metosulam, flumetsulam, florasulam, and diclosulam) in soy milk by capillary electrophoresis‐mass spectrometry (CE‐MS) is presented. The main electrospray interface (ESI) parameters (nebulizer pressure, dry gas flow rate, dry gas temperature, and composition of the sheath liquid) are optimized using a central composite design. To increase the sensitivity of the CE‐MS method, an off‐line sample preconcentration procedure based on solid‐phase extraction (SPE) is combined with an on‐line stacking procedure (i. e. normal stacking mode, NSM). Samples could be injected for up to 100 s, providing limits of detection (LODs) down to 74 μg/L, i. e., at the low ppb level, with relative standard deviation values (RSD,%) between 3.8% and 6.4% for peak areas on the same day, and between 6.5% and 8.1% on three different days. The usefulness of the optimized SPE‐NSM‐CE‐MS procedure is demonstrated through the sensitive quantification of the selected pesticides in soy milk samples.