Research Institute for Pesticides and Water, University Jaume I, Castellon 12071, Spain.
J Chromatogr A. 2013 May 31;1292:132-41. doi: 10.1016/j.chroma.2012.12.007. Epub 2012 Dec 13.
The determination of glyphosate (GLY) in soils is of great interest due to the widespread use of this herbicide and the need of assessing its impact on the soil/water environment. However, its residue determination is very problematic especially in soils with high organic matter content, where strong interferences are normally observed, and because of the particular physico-chemical characteristics of this polar/ionic herbicide. In the present work, we have improved previous LC-MS/MS analytical methodology reported for GLY and its main metabolite AMPA in order to be applied to "difficult" soils, like those commonly found in South-America, where this herbicide is extensively used in large areas devoted to soya or maize, among other crops. The method is based on derivatization with FMOC followed by LC-MS/MS analysis, using triple quadrupole. After extraction with potassium hydroxide, a combination of extract dilution, adjustment to appropriate pH, and solid phase extraction (SPE) clean-up was applied to minimize the strong interferences observed. Despite the clean-up performed, the use of isotope labelled glyphosate as internal standard (ILIS) was necessary for the correction of matrix effects and to compensate for any error occurring during sample processing. The analytical methodology was satisfactorily validated in four soils from Colombia and Argentina fortified at 0.5 and 5mg/kg. In contrast to most LC-MS/MS methods, where the acquisition of two transitions is recommended, monitoring all available transitions was required for confirmation of positive samples, as some of them were interfered by unknown soil components. This was observed not only for GLY and AMPA but also for the ILIS. Analysis by QTOF MS was useful to confirm the presence of interferent compounds that shared the same nominal mass of analytes as well as some of their main product ions. Therefore, the selection of specific transitions was crucial to avoid interferences. The methodology developed was applied to the analysis of 26 soils from different areas of Colombia and Argentina, and the method robustness was demonstrated by analysis of quality control samples along 4 months.
由于草甘膦（GLY）这种除草剂的广泛使用以及评估其对土壤/水环境影响的需求，因此测定土壤中的草甘膦含量具有重要意义。然而，其残留的测定非常复杂，特别是在有机质含量高的土壤中，通常会观察到强烈的干扰，而且由于这种极性/离子型除草剂的特殊物理化学特性。在本工作中，我们改进了之前报道的用于测定草甘膦及其主要代谢物 AMPA 的 LC-MS/MS 分析方法，以便应用于“困难”土壤，如在南美洲常见的土壤，这种除草剂在大豆或玉米等其他作物的大面积土地上广泛使用。该方法基于 FMOC 衍生化，然后进行 LC-MS/MS 分析，采用三重四极杆。用氢氧化钾提取后，采用提取稀释、调整至适当 pH 值和固相萃取（SPE）净化相结合的方法，以最大限度地减少观察到的强烈干扰。尽管进行了净化，但仍需要使用草甘膦同位素标记内标（ILIS）来校正基质效应，并补偿样品处理过程中可能出现的任何误差。该分析方法在哥伦比亚和阿根廷的四种土壤中进行了验证，这些土壤的浓度分别为 0.5 和 5mg/kg。与大多数推荐采集两个转换的 LC-MS/MS 方法不同，需要监测所有可用的转换来确认阳性样品，因为其中一些会受到未知土壤成分的干扰。这不仅发生在 GLY 和 AMPA 上，也发生在 ILIS 上。QTOF MS 分析有助于确认存在干扰化合物，这些化合物与分析物的名义质量相同，并且还存在一些主要的产物离子。因此，选择特定的转换对于避免干扰至关重要。该方法已应用于分析来自哥伦比亚和阿根廷不同地区的 26 种土壤，并且通过在 4 个月内分析质量控制样品证明了该方法的稳健性。
