Method Development for Aminopyralid Residues Determination by Ultra-High-Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry in Straw

Straw is an important by-product of crop production. It has been widely used as a feed as well as in fruit–vegetable production due to exerting a positive impact on soil and crop health and quality in the operated areas. On the other hand, applied crop-specific herbicides throughout the production stage, like aminopyralid (AP), may lead to significant plant injuries in sensitive vegetable plantations, even in very low concentrations. This study aims to optimize a short time, minimal consumables needed, and sensitive extraction and analytical method for AP residues in straw material using LC-MS/MS. For this purpose, standard AP signal response in acetonitrile (MeCN) and 1% of formic acid (FA) in methanol (MeOH) were tested; several chromatographic separation and mass spectroscopy (MS) parameters were improved and optimized. Subsequently, two different extraction methods were performed in AP spiked straw samples, and extraction efficacies were compared. Salting-out assisted liquid–liquid extraction (SALLE) by acidified MeCN combined with final dissolution in MeOH with 1% of FA prior to the analysis was chosen as the most appropriate method for the straw matrix. This method was then used for validation and real sample test analysis. The limit of quantification (LOQ) of AP in this optimized extraction method achieved 10 ng/g straw with a recovery rate of 71% and 13% RSD. The method was also tested on field straw mulch samples and 22.54 ± 0.8 ng/g of AP was detected.