Comprehensive gas chromatography coupled to mass spectrometry for the separation of pesticides in a very complex matrix

The present research is focused on the development of a comprehensive two-dimensional gas chromatography–rapid scanning quadrupole mass spectrometric (GC x GC-qMS) methodology for the analysis of trace-amount pesticides contained in a complex real-world sample. Reliable peak assignment was carried out by using a recently developed, dedicated pesticide MS library (for comprehensive GC analysis), characterized by a twin-filter search procedure, the first based on a minimum degree of spectral similarity and the second on the interactive use of linear retention indices (LRI). The library was constructed by subjecting mixtures of commonly used pesticides to GC x GC-qMS analysis and then deriving their pure mass spectra and LRI values. In order to verify the effectiveness of the approach, a pesticide-contaminated red grapefruit extract was analysed. The certainty of peak assignment was attained by exploiting both the enhanced separation power of dual-oven GC x GC and the highly effective search procedure.     

毛细管气相色谱法测定烟草及烟气中有机氯农药残留量

烟草样品或从卷烟烟气中收集到的固态悬浮颗粒样品以正己烷在索氏提取器中提取,提取液用弗罗里硅土固相萃取净化,所得溶液经蒸缩至5mL后,供气相色谱法测定。采用DB-5弹性石英毛细管柱分离样品,电子捕获检测器检测,共测定了17种有机氯农药(OCP′s),其检出限(3S/N)在0.02～0.10μg.g-1范围内。平均加标回收率为86%～92%,相对标准偏差(n=7)为3.0%～4.1%。     

Identification of unknown compounds on the basis of retention index data in comprehensive two-dimensional gas chromatography

The identification of unknown compounds in complex samples is very difficult. Comprehensive two-dimensional gas chromatography (GC x GC) provides very good resolution and improved identification reliability. Mass spectrometry is a powerful identification tool and retention index data are another good approach to this end. In this study, a second-order polynomial was used to calculate retention index data based on n-alkanes beyond the region of the 'isovolatile' curve in GC x GC, and the results in the 2nd dimension were validated by using the same stationary phase column in one-dimensional GC. To test the usefulness of the method, volatile compounds in a tobacco leaf extract fraction were analyzed using GC x GC, and 60 compounds were identified on the basis of their retention indices.     

气相色谱双柱法和气相色谱-质谱法在蔬菜农药多残留检测中的应用

在各种蔬菜的多种残留农药的检测中，蔬菜的基体常对农药的检测带来严重干扰。试样的预处理选用了较为简单的乙腈萃取法，以避免造成农药的损失。有机含磷农药的GC检测采用FPD检测器，而有机含氯农药及菊酯类农药用GC-ECD检测器，为了使被测农药能与干扰物质达到更好的分离，采用了具有不同极性的两个色谱柱。尽管如此，有时仍可能获得假结果（例如假阳性结果等）。为此进一步采用GC与MS联用的检测措施，使上述问题得以澄清。按所提出的方法，使多种共存的农药的检测，在准确性及可靠性方面得到很大提高。     

Evaluation of two-dimensional gas chromatography-time-of-flight mass spectrometry for the determination of multiple pesticide residues in fruit

In recent years, comprehensive two-dimensional gas chromatography (GC x GC) has attained increasing attention for its outstanding separation potential and capability to solve demanding analytical tasks. Trace level analysis of pesticides residues in complex food matrices represents such a demanding task. For some commodities, such as baby food, the requirements on method detection limits are very strict and the unambiguous confirmation of the pesticide presence based on mass spectrometric detection is required. In this work, GC x GC coupled to time-of-flight mass spectrometry (TOF MS) has been evaluated for the determination of pesticides residues in fruit samples. Twenty modern pesticides with a broad range of physico-chemical properties were analysed in apple and peach samples. It has been demonstrated that the application of comprehensive two-dimensional gas chromatography brings distinct advantages such as enhanced separation of target pesticides from matrix co-extracts as well as their improved detectability. The limits of detection of the pesticides comprised in the study (determined at S/N = 5) ranged from 0.2 to 30 pg, injected with the exception of the last eluted deltamethrin, for which 100 pg could be detected. When compared to one-dimentional GC-TOF MS analysis under essentially the same conditions the detectability enhancement was 1.5-50-fold. Full mass spectral information by time-of-flight mass spectrometry and the deconvolution capability of the dedicated software allowed for reliable identification of most pesticides at levels below 0.01 mg/kg (< 10 pg injected) in fruit. Performance characteristics of the GC x GC-TOF MS method, such as linearity of calibration curves, repeatability of (summed) peak areas, as well as repeatability of first and second dimension retention times, were shown to fully satisfy the requirements for trace level analysis of the pesticide residues in food.     

Gas chromatographic–mass spectrometric methodology using solid-phase microextraction for the multiresidue determination of pesticides in surface waters

Solid-phase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and selected ion monitoring (SIM) was used for the analytical determination of priority pesticide residues. Fibers coated with a 65-µm film thickness of polydimethylsiloxane divinylbenzene (PDMS-DVB) were used to extract 31 pesticides of different chemical groups. The quality parameters of the method demonstrated a good precision with detection limits of 1–56?ng/L. Linearity was controlled in the range of 0.1–50?µg/L. The proposed method was applied for the trace-level determination of the target pesticides in surface water samples including three rivers and one lake at the Epirus region (north-west Greece) for a period of one year. The results demonstrate the suitability of the SPME–GC–MS approach for the analysis of multi-residue pesticides in environmental water samples.     

Development of a rapid screening technique for organochlorine pesticides using solvent microextraction (SME) and fast gas chromatography (GC)

A novel, fast screening method for organochlorine pesticides (OCPs) in water samples has been developed. Total analysis time was less than 9 min, allowing 11 samples to be screened per hour. The relatively new technique of solvent microextraction (SME) was used to extract and preconcentrate the pesticides into a single drop of hexane. The use of a conventional carbon dioxide cryotrap was investigated for introduction of the extract onto a micro-bore (0.1 mm) capillary column for fast GC analysis. A pulsed-discharge electron capture detector was used which yielded selective and sensitive measurement of the pesticide peaks. Fast GC conditions were optimised and tested with the previously developed SME procedure. Calibration curves yielded good linearity and concentrations down to 0.25 ng mL-1 were detectable with RSD values ranging from 12.0 to 28% and LOD for most OCPs at 0.25 ng mL-1. Spiked river water samples were tested and using the developed screen we were able to differentiate between spiked samples and samples containing no OCPs.     

气相色谱-串联质谱技术分析烟草中的132种农药残留

利用气相色谱-串联质谱(GC-MS/MS)检测技术,建立了检测烟草中的132种农药残留的高灵敏度方法。分析过程中考察了不同萃取溶剂、不同缓冲盐体系、不同净化剂对目标物回收率的影响。最终确定烟草样品以乙腈进行提取,以N-丙基乙二胺(PSA)与碳18(C18E)的混合净化剂进行净化,氮气吹近干后用正己烷-丙酮(9:1, v/v)复溶,过有机滤膜后进行GC-MS/MS测定,内标法定量。132种农药在20～2000 μg/kg之间线性关系良好(r2 ＞0.99);所有农药的方法定量限(LOQ, S/N=10)均低于20 μg/kg;在50、200、500 μg/kg的加标水平下,除灭蚁灵及六氯苯回收率稍低外,其他农药的平均回收率为68.10%～123.15%,相对标准偏差(RSD)为1.79%～19.88%。对国际烟草科学研究合作中心(CORESTA)2012年共同实验的烟草样品进行检测,对比本方法与已有的标准方法,其结果一致性较好。该方法准确、可靠,灵敏度好,适用于烟草中132种农药残留的快速筛查与定性、定量分析。     

Fast and sensitive determination of pesticide residues in vegetables using low-pressure gas chromatography with a triple quadrupole mass spectrometer

In this study, the feasibility of low-pressure gas chromatography (LP-GC) in conjunction with a triple quadrupole mass spectrometer, as a route towards fast pesticide residue analysis, was investigated. A Varian GC-MS system equipped with a mass spectrometer model 1200 was used. LP-GC-MS experiments were performed on a HP-5 10 m x 0.32 mm x 0.25 microm analytical column connected to a 2.5 m x 0.15 mm non-coated restriction precolumn at the inlet end. For comparison purposes conventional GC-MS analysis was performed on a RTX-5 30 m x 0.25 mm x 0.5 microm column. Under the optimized conditions the analysis time was reduced to 13.3 min with the LP-GC approach which corresponds to an almost threefold gain in speed versus the conventional GC (37 min). Despite the poorer separation power of the LP-GC column, the experiments conducted with tomato and onion extracts spiked with 78 pesticides proved that LP-GC-MS is of practical value to perform full scan screening analysis. Moreover, the rate of false negative results was higher in the case of conventional GC-MS while the LP-GC-MS enabled correct identification of pesticides at lower levels since the peaks were improved in both size and shape. Validation experiments were performed on a sample of 12 representative pesticides for comparison of performance characteristics of the LP-GC and GC approaches with mass spectrometer operated in scan, SIM and MS/MS mode. The LP-GC column set-up interfaced to the MS detector was found to be superior to the conventional GC with respect to obtained linearity, accuracy and precision parameters. Also, lower limits of detection in real extracts were achieved using the LP-GC approach. Finally, the LP-GC-MS/MS analysis of tomato samples with incurred pesticide residues demonstrated the applicability of the developed method for analysis of real samples.     

Use of graphitic carbon black and primary secondary amine for determination of 17 organophosphorus pesticide residues in spinach

Graphitized carbon black (GCB) and primary secondary amine (PSA) as dispersive-SPE sorbents were applied to optimize the method for the determination of 17 organophosphorus pesticides in spinach which contained so many pigments using GC with flame photometric detector (FPD). The sample was extracted with ACN, and an aliquot of the extract was concentrated to near dryness. Ethyl acetate or acetone was chosen as the dissolving solvent. Subsequently, dispersive-SPE was used for cleanup, and the type and quantity of sorbents (GCB, PSA and activated carbon) were tested in the experiments. The best results were when acetone was used to dissolve and 30 mg each of GCB and PSA for cleanup. In this condition, recoveries of pesticides analyzed were between 52-117% with RSD below 10%, and LOQ ranged from 10 to 20 microg/kg. This method was simple, effective and efficient, and can protect the GC system to some extent.     

Dual NPD/ECD detection in comprehensive two-dimensional gas chromatography for multiclass pesticide analysis

A comprehensive 2-D GC (GC x GC) dual detection system, coupled to nitrogen-phosphorus detection (NPD) and electron capture detection (ECD) has been developed for multiclass pesticide analysis in vegetable sample matrices. The second dimension column was connected to the parallel detectors via a microfluidic splitting device. The sample set comprised 17 organochlorine pesticides, 15 organophosphorus insecticides and 9 N-containing fungicides. Selective detection of vegetable sample extracts provides increased information content through simultaneous, correlated GC x GC plots for both ECD and NPD, which demonstrated improved separation of pesticide standards from each other, and from the sample matrix. The efficiency of NPD and ECD modes was investigated and compared; the ECD produced broader peaks, with the ECD generating greater response as measured by S/N ratio. Accuracy and precision of the approach were determined as repeatability and reproducibility for selected pesticides. The RSDs of the intraday (n = 5) and interday (3 days) analyses of the selected pesticides are less than 2.5 and 10%, respectively. The relative ratio of the ECD/NPD response is proposed to offer additional identification of individual pesticides, in addition to the (1)t(R) and (2)t(R) retention coordinates; ratios vary from 19 to over 1000 for selected pesticides that also exhibit ECD and NPD activities.     

Trace analysis of polychlorinated dibenzo-p-dioxins, dibenzofurans and WHO polychlorinated biphenyls in food using comprehensive two-dimensional gas chromatography with electron-capture detection

Trace analysis of 2,3,7,8-polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and the 12 WHO-PCBs (four non-ortho and eight mono-ortho congeners that have been assigned toxic equivalence factors, TEFs, by the World Health Organisation) was conducted by comprehensive two-dimensional gas chromatography with a micro electron-capture detector (GC x GC-microECD). Four food matrices (fish oil from herring, spiked cows' milk, vegetable oil and an eel extract) were analysed by two GC x GC laboratories, and four GC-HRMS laboratories generated reference values. The two GC x GC laboratories used different column combinations for separating the target analytes. For the first dimension, non-polar DB-XLB and VF-1 columns were used, and for the second dimension, an LC-50 liquid crystalline column with unique selectivity for planar compounds. The congener-specific and total toxic equivalence (TEQ) data obtained using DB-XLB x LC-50 were in good agreement with results obtained by the GC-HRMS laboratories. The WHO-PCB data obtained with the VF-1 x LC-50 combination was also good, but the PCDD/F concentrations were sometimes overestimated due to matrix interferences. GC x GC-microECD using DB-XLB x LC-50 seems to fulfil the European Community requirements of a screening method for PCDD/F and WHO-PCB TEQ in food.     

A simple and inexpensive "solvent in silicone tube extraction" approach and its evaluation in the gas chromatographic analysis of pesticides in fruits and vegetables

A novel, simple, and inexpensive approach to sorptive extraction, which we call solvent in silicone tube extraction (SiSTEx), was applied to pesticide residue analysis and its effectiveness and efficiency were evaluated. In SiSTEx, which is a form of open tubular sorptive extraction, a piece of silicone tubing (4 cm long, 1.47 mm ID, 1.96 mm OD in this study) is attached to the cap of a 20 mL glass vial that contains the aqueous sample. The tubing is plugged at the end dangling in the sample solution, and MeCN (e.g., 40 microL) added by syringe to the inner tube volume through a septum in the cap. A stir-bar is used to mix the sample for a certain time (e.g., 60 min), which allows chemicals to partition into the tubing where they diffuse across the silicone and partition into the MeCN. The final MeCN extract is then analyzed for the concentrated analytes. In this study, the SiSTEx approach was evaluated for the analysis of organophosphorus (OP) and organochlorine (OC) pesticides in fruits and vegetables using GC/pulsed flame photometric (PFPD) and halogen specific (XSD) detectors for analysis. The produced samples were initially extracted by a rapid MeCN procedure, and 5 mL of the initial extract was diluted four-fold with water to undergo sorptive extraction for 60 min. The final extract was analyzed by GC/PFPD + XSD for 14 OP and 22 OC pesticides. This simple approach was able to detect 26 of the 36 pesticides at 10 ng/g or less original equivalent sample concentration with average reproducibility of 11% RSD. For those 26 pesticides, a 44-fold lower detection limit on average was achieved in matrix extracts using SiSTEx despite the four-fold dilution with water.     

Gas chromatography analysis of organophosphorous pesticides in plant samples

Summary The work presents a GC method for the determination of six organophosphorous pesticide residues in cabbage. Chopped cabbage was blended with acetone, then extracted with the mixture of n-hexane:methylene chloride (1:1). The extract was purified on a GPC column packed with BioBeads SX-3 gel. The pesticides were eluted with the mixture of methylene chloride:cyclohexane (1:1) at the flow rate of 0.5 mL min⁻¹. After concentrating the extract was analysed by GC. Nearly 100 samples of cabbage were analysed; trace residues of dimethoate (about 0.05 ppm) were found in 10 samples. The average recoveries of the pesticides were above 80% with a relative standard deviation mostly less than 10%. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

用于气相色谱和气相色谱-质谱测定植物样品中含氯有机污染物残留的样品前处理方法

根据植物样品中的主要干扰物质,建立了用于气相色谱(GC)和气相色谱-质谱联用(GC-MS)测定植物样品中含氯有机污染物残留的样品前处理方法,有效提高了对植物样品中有机氯农药及多氯联苯检测的灵敏度。采用均质提取法对样品进行提取,考察了凝胶渗透色谱(GPC)和固相萃取(SPE)对提取液的净化效果。结果发现,采用GC测定目标物时,提取液需经GPC和SPE两次净化;而采用GC-MS测定目标物时,仅用SPE一次净化即可。该方法快速、经济、灵敏,适合多种植物样品中有机污染物残留分析的样品前处理要求。     

Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography-mass spectrometry (LP-GC-MS). No special techniques for injection or detection with a common quadrupole GC-MS instrument were required to use this approach. The LP-GC-MS approach used an analytical column of 10 m x 0.53 mm I.D., 1 microm film thickness coupled with a 3 m x 0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC-MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC-MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC-MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC-MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC-MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.     

蔬菜中有机氯农药残留的超临界流体提取和气相色谱法测定

建立了用超临界流体萃取、气相色谱测定韭菜中百菌清、艾氏剂、狄氏剂、异狄氏剂残留量的方法。样品与无水硫酸镁混合后进行萃取。用正交设计法选择萃取条件,最佳条件为压力３０．４ＭＰａ,温度４０℃。静态萃取时间１ｍｉｎ,ＣＯ２用量１５ｍＬ,收集液为乙酸乙酯。     

Determination of organophosphorus pesticides in fruits by on-line size-exclusion chromatography-liquid chromatography-gas chromatography-flame photometric detection.

The determination of organophosphorus pesticides in fruits by size-exclusion chromatography (SEC) on a polystyrene column coupled on-line to a gas chromatography (GC) system was unsatisfactory as a result of interfering peaks in GC. A liquid chromatography step on silica gel was therefore inserted between the SEC and GC steps to filter out polar by-products. Samples of fruit (apples, grapes and kiwi fruits) were extracted, then the extract filtered or centrifuged and injected into an automated on-line SEC-liquid chromatography-GC-flame photometric detection. Recoveries were about 95% and the detection limits about 1 ng/g.     

乙腈-无机盐-水双水相体系萃取-气相色谱法检测鱼肉中拟除虫菊酯

以乙腈-无机盐-水双水相体系,建立了一种环保、高效的用于气相色谱法检测鱼肉样品中拟除虫菊酯的样品前处理方法.实验利用荧光猝灭法与气相色谱法研究了拟除虫菊酯药物在以蛋白质为主要基质的水产品中的存在状态,考察了双水相的形成条件,并探讨了蛋白质对双水相萃取率的影响.结果表明,拟除虫菊酯药物通过疏水作用力与蛋白质牢固结合.以体积分数为80%的乙腈水溶液作为萃取液可以引起水产品中的蛋白质基质缓慢而彻底地变性,从而充分释放与蛋白质结合的药物,实现拟除虫菊酯的均相高效萃取.80%的乙腈水溶液具有较强的化学极性,因而在双水相系统上相中与药物残留共同萃入的脂溶性杂质较少,萃取液净化步骤大大简化.在双水相上相中加入无水MgSO4,PSA去除水分与杂质后,直接进样进行气相色谱检测.该方法用于鱼肉样品中六种拟除虫菊酯的萃取检测,回收率为81.1%～96.4%,检出限为8～14ng·mL-1.     

Determination of multiresidue pesticides in green tea by using a modified QuEChERS extraction and ion-trap gas chromatography/mass spectrometry

The pesticide residues in exported and imported tea products must not exceed the maximum residue limits (MRLs) regulated by the import countries. Tea is a complex matrix that obfuscates the determination of pesticide residues. Many available methods for multiresidue pesticide analysis of tea are time-consuming and require many cleanup steps. The objective of this study was to develop a simple multiresidue method by using a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and ion-trap GC/MS/MS, which can identify, confirm, and quantify pesticides in complex matrixes. A tea product was homogenized with water, and the pesticides were extracted with acetonitrile containing 1% acetic acid. The extract was subjected to centrifugation, initial cleanup with dispersive SPE (dSPE), solvent exchange, and final cleanup with dSPE. Diethyl-d10-parathion and triphenyl phosphate were used as the internal standard and surrogate, respectively. The final extract was injected into an ITQ 700 gas chromatograph/mass spectrometer. Quantitation of individual pesticides was based on matrix-matched calibration curves with a correlation coefficient of > 0.9930 for the 22 pesticides selected for the study. The recoveries of the 22 pesticides ranged from 78 to 115%, except those for diazinon (130%) and malathion (122%), with an average RSD of 8.7%. The LOD values of all of the pesticides, except for terbufos, were below the MRLs set by the European Union and Japan.