Department of Chemistry, University of Pretoria, Hatfield, South Africa.
Anal Chim Acta. 2012 Jun 12;730:120-6. doi: 10.1016/j.aca.2012.03.028. Epub 2012 Mar 27.
In rural parts of South Africa the organochlorine insecticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) is still used for malaria vector control where traditional dwellings are sprayed on the inside with small quantities of technical DDT. Since o,p'-DDT may show enantioselective oestrogenicity and biodegradability, it is important to analyse enantiomers of o,p'-DDT and its chiral degradation product, o,p'-DDD, for both health and environmental-forensic considerations. Generally, chiral analysis is performed using heart-cut multidimensional gas chromatography (MDGC) and, more recently, comprehensive two-dimensional gas chromatography (GC×GC). We developed an off-line gas chromatographic fraction collection (heart-cut) procedure for the selective capturing of the appropriate isomers from a first apolar column, followed by reinjection and separation on a second chiral column. Only the o,p'-isomers of DDT and DDD fractions from the first dimension complex chromatogram (achiral apolar GC column separation) were selectively collected onto a polydimethylsiloxane (PDMS) multichannel open tubular silicone rubber trap by simply placing the latter device on the flame tip of an inactivated flame ionisation detector (FID). The multichannel trap containing the o,p'-heart-cuts was then thermally desorbed into a GC with time-of-flight mass spectrometry detection (GC-TOFMS) for second dimension enantioselective separation on a chiral column (β-cyclodextrin-based). By selectively capturing only the o,p'-isomers from the complex sample chromatogram, (1)D separation of ultra-trace level enantiomers could be achieved on the second chiral column without matrix interference. Here, we present solventless concentration techniques for extraction of DDT from contaminated soil and air, and report enantiomeric fraction (EF) values of o,p'-DDT and o,p'-DDD obtained by a new multidimensional approach for heart-cut gas chromatographic fraction collection for off-line second dimension enantiomeric separation by (1)D GC-TOFMS of selected isomers. This multidimensional method is compared to the complementary technique of comprehensive GC×GC-TOFMS using the same enantioselective column, this time as the first dimension of separation.
在南非农村地区，仍在使用有机氯杀虫剂滴滴涕（1,1,1-三氯-2,2-双（对氯苯基）乙烷）来控制疟疾媒介，在那里，传统住宅的内部会用少量的滴滴涕进行喷洒。由于 o,p'-滴滴涕可能表现出对映选择性雌激素活性和生物降解性，因此分析 o,p'-滴滴涕及其手性降解产物 o,p'-滴滴滴的对映异构体对于健康和环境取证都很重要。通常，手性分析是使用多维气相色谱（MDGC）进行的，最近则使用全二维气相色谱（GC×GC）。我们开发了一种离线气相色谱馏分收集（切分）程序，用于从第一个非极性柱中选择性捕获合适的异构体，然后在第二个手性柱上重新注入和分离。只有来自第一维复杂色谱图（非手性非极性 GC 柱分离）的滴滴涕和滴滴滴的 o,p'-异构体，通过简单地将后者装置放置在已失活的火焰离子化检测器（FID）的火焰尖端上，才能被选择性地收集到聚二甲基硅氧烷（PDMS）多通道开放式管状硅橡胶捕集器上。多通道捕集器包含 o,p'-切分，然后通过热解吸进入带有飞行时间质谱检测的 GC（GC-TOFMS），在手性柱（基于β-环糊精）上进行第二维对映选择性分离。通过从复杂的样品色谱图中仅选择性地捕获 o,p'-异构体，可以在第二手性柱上实现超低痕量对映体的（1)D 分离，而不会受到基质干扰。在这里，我们提出了从污染土壤和空气中提取滴滴涕的无溶剂浓缩技术，并报告了通过多维切分气相色谱馏分收集方法获得的 o,p'-滴滴涕和 o,p'-滴滴滴的对映体分数（EF）值，该方法用于离线第二维对映体分离，通过（1)D GC-TOFMS 对选定异构体进行选择。与使用相同手性柱的互补技术——全面 GC×GC-TOFMS 相比，这种多维方法作为分离的第一维。
