Organic acids (OAs) play an essential role in several cellular biochemical pathways. Released by plant roots, OAs can help them tolerate phytotoxic forms of aluminum (Al) present in acidic soils. Some studies use high-performance liquid chromatography (HPLC), ion chromatography and, more rarely, gas chromatography-mass spectrometry (GC–MS) to analyze exuded OAs, but they are limited to hours or 1–2 days. The main limitation is that OAs are measured only in CaCl₂ and AlCl₃ solutions, and not in “complete” nutrient solutions, only enabling short-term collection of secreted OAs. Here, we aimed to test a method to quantify citric, malic, oxalic and succinic acids in “complete” nutrient solution with 0, 740 and 1480 μM Al, using a GC–MS. First, a calibration curve was established through a chromatogram that was generated using six concentrations of OAs in methanol. Thus, samples containing OAs only were derived by methylation. Then, analytical curves were set up using seven OAs concentrations added in the three nutrient solutions. The OAs were concentrated by drying the solutions. After re-suspension, samples were derived by methylation. Instrumental precision and the method repeatability were also checked. Chromatograms showed adequate resolution, with distinct peak heights between OAs concentrations and their respective retention times. Both calibration and analytical curves indicated consistent linearity (R > 0.99), evidencing the method and equipment parameters were able to provide results directly proportional to OAs concentrations. This low-cost method is recommended for evaluation of Al-induced OA secretion by roots of whole plants in nutrient solutions for several days or weeks.

中文翻译：

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利用GC-MS定量营养液中植物根系铝诱导的有机酸分泌的方法

有机酸（OAs）在几种细胞生化途径中起着至关重要的作用。OAs通过植物根部释放，可以帮助它们耐受酸性土壤中存在的植物毒性形式的铝（Al）。一些研究使用高效液相色谱（HPLC），离子色谱，以及更罕见的是气相色谱-质谱（GC-MS）来分析渗出的OA，但仅限于数小时或1-2天。主要限制是仅在CaCl ₂和AlCl ₃中测量OAs解决方案，而不是“完整的”营养液，只能短期收集分泌的OA。在这里，我们旨在测试一种使用GC-MS定量测定0、740和1480μMAl的“完全”营养液中柠檬酸，苹果酸，草酸和琥珀酸的方法。首先，通过色谱图建立校正曲线，该色谱图使用六种浓度的OAs在甲醇中生成。因此，仅包含OA的样品是通过甲基化得到的。然后，使用添加到三种营养液中的七个OAs浓度建立分析曲线。通过干燥溶液浓缩OA。重新悬浮后，样品通过甲基化得到。还检查了仪器的精密度和方法的可重复性。色谱图显示足够的分辨率，在OAs浓度及其各自的保留时间之间具有明显的峰高。校准曲线和分析曲线均显示出一致的线性（R> 0.99），证明方法和设备参数能够提供与OAs浓度成正比的结果。建议使用这种低成本方法评估营养液中整株植物根系铝诱导的OA分泌数天或数周。