Department of Water and Environmental Studies, Linköping University, SE-58183 Linköping, Sweden.
Chemosphere. 2013 Feb;90(6):1821-8. doi: 10.1016/j.chemosphere.2012.09.020. Epub 2012 Oct 6.
Environmental monitoring of pesticide residues in surface water is often done with time-integrated sampling where a specified volume is sampled each hour during, e.g., a week, thus avoiding at momentary high or low extreme concentrations. However, sampling over an extended period of time can result in losses of easily degradable analytes, why the stability of the target analytes over the timespan of the sampling must be checked. Glyphosate is one of the most widely used herbicides. Because of its chemical complexity, glyphosate binds differently to metals and colloids at different pH, and the degradation may also be affected. Recovery of glyphosate from spiked natural waters after 1 and 3 weeks of storage was higher when the samples were acidified to approximately pH 2 rather than at their natural pH. Keeping the samples refrigerated to 4°C in darkness also enhanced recovery, while glyphosate losses were substantial from samples kept at their natural pH at 20 °C. Total loss of glyphosate was observed in some samples kept at natural pH, 20 °C, and daylight; a loss partly due to binding to metals or colloids that could only partially be reversed by acidification. For 1-week time-integrated sampling a small amount of hydrochloric acid in a piece of heat-sealed hydrophobic micro-porous tubing is added to the sampling bottles before deployment, a procedure that acidifies the samples during collection keeping them below pH 2 until analysis, thus minimising losses of glyphosate. The method also allows determination of the primary degradation product aminomethylphosphonic acid (AMPA).
环境监测农药残留地表水通常采用时间积分采样，即每周每个小时采集指定体积的水样，从而避免瞬时高或低的极端浓度。然而，长时间采样可能导致易降解分析物的损失，因此必须检查目标分析物在采样时间段内的稳定性。草甘膦是最广泛使用的除草剂之一。由于其化学复杂性，草甘膦在不同 pH 值下与金属和胶体的结合方式不同，降解也可能受到影响。将加标天然水样品在 4°C 黑暗条件下冷藏，同时将样品酸化至约 pH 2 而不是其天然 pH 值，可提高草甘膦的回收率。在 20°C 自然 pH 值下保存的样品中，草甘膦损失较大，而在 20°C 自然 pH 值和光照条件下，一些样品中的草甘膦完全损失；部分损失归因于与金属或胶体的结合，仅通过酸化部分逆转。对于 1 周的时间积分采样，在部署前向采样瓶中添加少量盐酸，并用热封疏水性微孔管密封，这一过程会在收集过程中酸化样品，使其 pH 值保持在 2 以下，直到分析完成，从而最大程度地减少草甘膦的损失。该方法还允许测定主要降解产物氨甲基膦酸（AMPA）。
