Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907, USA.
Center for Plant Biology, Purdue University, West Lafayette, IN 47907, USA.
Molecules. 2020 Aug 11;25(16):3649. doi: 10.3390/molecules25163649.
Dicamba is a moderately volatile herbicide used for post-emergent control of broadleaf weeds in corn, soybean, and a number of other crops. With increased use of dicamba due to the release of dicamba-resistant cotton and soybean varieties, growing controversy over the effects of spray drift and volatilization on non-target crops has increased the need for quantifying dicamba collected from water and air sampling. Therefore, this study was designed to evaluate stable isotope-based direct quantification of dicamba from air and water samples using single-quadrupole liquid chromatography-mass spectrometry (LC-MS). The sample preparation protocols developed in this study utilize a simple solid-phase extraction (SPE) protocol for water samples and a single-step concentration protocol for air samples. The LC-MS detection method achieves sensitive detection of dicamba based on selected ion monitoring (SIM) of precursor and fragment ions and relies on the use of an isotopically labeled internal standard (IS) (D-dicamba), which allows for calculating recoveries and quantification using a relative response factor (RRF). Analyte recoveries of 106-128% from water and 88-124% from air were attained, with limits of detection (LODs) of 0.1 ng mL and 1 ng mL, respectively. The LC-MS detection method does not require sample pretreatment such as ion-pairing or derivatization to achieve sensitivity. Moreover, this study reveals matrix effects associated with sorbent resin used in air sample collection and demonstrates how the use of an isotopically labeled IS with RRF-based analysis can account for ion suppression. The LC-MS method is easily transferrable and offers a robust alternative to methods relying on more expensive tandem LC-MS/MS-based options.
二甲苯草胺是一种挥发性中度的除草剂，用于玉米、大豆和其他一些作物的苗后阔叶杂草的防治。由于抗二甲苯草胺棉花和大豆品种的释放，二甲苯草胺的使用增加，关于喷雾漂移和挥发对非靶标作物影响的争议也越来越多，这增加了从水样和空气样品中定量收集二甲苯草胺的需求。因此，本研究旨在评估使用单四极杆液相色谱-质谱（LC-MS）对来自水样和空气样品的二甲苯草胺进行基于稳定同位素的直接定量。本研究中开发的样品制备方案利用水样的简单固相萃取（SPE）方案和空气样品的单步浓缩方案。LC-MS 检测方法基于前体离子和碎片离子的选择离子监测（SIM）实现了对二甲苯草胺的灵敏检测，并依赖于使用同位素标记的内标（IS）（D-二甲苯草胺），这允许使用相对响应因子（RRF）计算回收率和定量。从水样中获得了 106-128%的分析物回收率，从空气中获得了 88-124%的回收率，检测限（LOD）分别为 0.1 ng mL 和 1 ng mL。LC-MS 检测方法不需要样品预处理，如离子对或衍生化，即可达到灵敏度。此外，本研究揭示了与空气样品采集用吸附树脂相关的基质效应，并展示了如何使用同位素标记 IS 和基于 RRF 的分析来校正离子抑制。LC-MS 方法易于转移，为依赖于更昂贵的串联 LC-MS/MS 方法的方法提供了一个强大的替代方案。
