TUM School of Natural Sciences, Chair of Analytical Chemistry and Water Chemistry, Technical University of Munich, 85748 Garching, Germany.
Anal Chem. 2023 May 23;95(20):7839-7848. doi: 10.1021/acs.analchem.2c05465. Epub 2023 May 11.
Compound-specific isotope analysis (CSIA) of organic water contaminants can provide important information about their sources and fate in the environment. Analyte enrichment from water remains nonetheless a critical yet inevitable step before measurement. Commercially available solid-phase extraction (SPE) sorbents are inherently nonselective leading to co-extraction of concurrent dissolved organic matter (DOM) and in turn to analytical interferences, especially for low-occurring contaminants. Here, we (i) increased extraction selectivity by synthesizing cyclodextrin polymers (α-, β-, γ-CDP) as SPE sorbents, (ii) assessed their applicability to carbon isotope analysis for a selection of pesticides, and (iii) compared them with commonly used commercial sorbents. Extraction with β-CDP significantly reduced backgrounds in gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and enhanced sensitivity by a factor of 7.5, which was further confirmed by lower carbon-normalized C/C ratios in corresponding extracts as derived from dissolved organic carbon (DOC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Gibbs free energies of adsorption demonstrated weak competition between DOM and analyte on the three CDPs. No isotopic fractionation (ΔδC within ± 0.3‰) was observed for the investigated pesticides after using β-CDP as an SPE sorbent covering a range of concentrations (5-500 μg L), flow velocities (5-40 cm min), and sorbent regeneration (up to six times). The present study highlights the benefit of selecting innovative extraction sorbents to avoid interferences in advance. This strategy in combination with existing cleanup approaches offers new prospects for CSIA at field concentrations of tens to hundreds of nanograms per liter.
有机水体污染物的化合物特定同位素分析 (CSIA) 可为其在环境中的来源和归宿提供重要信息。然而，在进行测量之前，从水中对分析物进行富集仍然是一个至关重要但不可避免的步骤。商业上可用的固相萃取 (SPE) 吸附剂本质上是非选择性的，这导致共提取同时存在的溶解有机物 (DOM)，并进而导致分析干扰，特别是对于低浓度存在的污染物。在这里，我们 (i) 通过合成环糊精聚合物（α-、β-、γ-CDP）作为 SPE 吸附剂来提高萃取选择性，(ii) 评估了它们对选择的农药进行碳同位素分析的适用性，以及 (iii) 将其与常用的商业吸附剂进行了比较。用 β-CDP 萃取可显著降低气相色谱-同位素比质谱 (GC-IRMS) 的背景，灵敏度提高了 7.5 倍，这通过从溶解有机碳 (DOC) 和液相色谱-串联质谱 (LC-MS/MS) 分析中得出的相应提取物中的碳归一化 C/C 比值更低得到了进一步证实。吸附的吉布斯自由能表明，在三种 CDP 上，DOM 和分析物之间的竞争较弱。在用 β-CDP 作为 SPE 吸附剂后，在所研究的农药的浓度范围（5-500μg/L）、流速（5-40cm/min）和吸附剂再生（多达六次）范围内，没有观察到同位素分馏（ΔδC 在 ± 0.3‰ 内）。本研究强调了选择创新萃取吸附剂预先避免干扰的好处。这种策略与现有的净化方法相结合，为在数十到数百纳克/升的田间浓度下进行 CSIA 提供了新的前景。
