García-Reyes Juan F, Jackson Ayanna U, Molina-Díaz Antonio, Cooks R Graham
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, USA.
Anal Chem. 2009 Jan 15;81(2):820-9. doi: 10.1021/ac802166v.
Desorption electrospray ionization (DESI) is applied to the rapid, in situ, direct qualitative and quantitative (ultra)trace analysis of agrochemicals in foodstuffs. To evaluate the potential of DESI mass spectrometry (MS) in toxic residue testing in food, 16 representative multiclass agricultural chemicals (pesticides, insecticides, herbicides, and fungicides) were selected (namely, ametryn, amitraz, azoxystrobin, bitertanol, buprofezin, imazalil, imazalil metabolite, isofenphos-methyl, malathion, nitenpyram, prochloraz, spinosad, terbuthylazine, thiabendazole, and thiacloprid). The DESI-MS experiments were performed using 3 microL of solution spotted onto conventional smooth poly(tetrafluoroethylene) (PTFE) surfaces, with examination by MS and tandem mass spectrometry (MS/MS) using an ion trap mass spectrometer. Optimization of the spray solvent led to the use of acetonitrile/water (80:20) (v/v), with 1% formic acid. Most of the compounds tested showed remarkable sensitivity in the positive ion mode, approaching that attainable with conventional direct infusion electrospray mass spectrometry. To evaluate the potential of the proposed approach in real samples, different experiments were performed including the direct DESI-MS/MS analysis of fruit peels and also of fruit/vegetable extracts. The results proved that DESI allows the detection and confirmation of traces of agrochemicals in actual market-purchased samples. In addition, MS/MS confirmation of selected pesticides in spiked vegetable extracts was obtained at absolute levels as low as 1 pg for ametryn. Quantitation of imazalil residues was also undertaken using an isotopically labeled standard. The data obtained were in agreement with those from the liquid chromatography mass spectrometry (LC-MS) reference method, with relative standard deviation (RSD) values consistently below 15%. The results obtained demonstrate the sensitivity of DESI as they meet the stringent European Union pesticide regulation requirements (maximum residue levels) for a large percentage of the studied compounds.
解吸电喷雾电离（DESI）被应用于食品中农用化学品的快速、原位、直接定性和定量（超）痕量分析。为评估DESI质谱法（MS）在食品有毒残留物检测中的潜力，选择了16种具有代表性的多类农用化学品（农药、杀虫剂、除草剂和杀菌剂）（即莠灭净、双甲脒、嘧菌酯、联苯三唑醇、噻嗪酮、抑霉唑、抑霉唑代谢物、甲基异柳磷、马拉硫磷、烯啶虫胺、咪鲜胺、多杀菌素、特丁津、噻菌灵和噻虫啉）。DESI-MS实验使用3微升点样于传统光滑聚四氟乙烯（PTFE）表面的溶液进行，通过离子阱质谱仪进行MS和串联质谱（MS/MS）检测。喷雾溶剂的优化导致使用乙腈/水（80:20）（v/v）和1%甲酸。大多数测试化合物在正离子模式下表现出显著的灵敏度，接近传统直接进样电喷雾质谱法所能达到的灵敏度。为评估所提出方法在实际样品中的潜力，进行了不同实验，包括对果皮以及水果/蔬菜提取物的直接DESI-MS/MS分析。结果证明，DESI能够检测和确认真实市场购买样品中的痕量农用化学品。此外，在加标蔬菜提取物中对选定农药进行MS/MS确证时，莠灭净的绝对含量低至1皮克。还使用同位素标记标准对抑霉唑残留进行了定量。获得的数据与液相色谱质谱（LC-MS）参考方法的数据一致，相对标准偏差（RSD）值始终低于15%。所获得的结果证明了DESI的灵敏度，因为它们满足了欧盟对大部分研究化合物的严格农药法规要求（最大残留限量）。
