Confirmation of chlorotriazine pesticides,their degradation products and organophosphorus pesticides in soil samples using gas chromatography-mass spectrometry with electron impact and positive- and negative-ion chemical ionization

Gas chromatography-mass spectrometry (GC-MS) with electron impact (EI), positive-ion chemical ionization (PCI) and negative-ion chemical ionization (NCI) were applied as confirmatory techniques for residue analysis of chlorotriazine pesticides, their degradation products and organophosphorus pesticides in soil samples. Clean-up was effected using a Florisil column with subsequent analysis by GC with a nitrogen-phosphorus detector. GC-MS with the EI mode of operation is the common mode of confirmation for all the pesticides. Further confirmation by either GC-MS with PCI and NCI for chlorotriazines and organophosphorus pesticides, respectively, is recommended. The method was applied to the determination of residue levels of atrazine, deethylatrazine, deisopropylatrazine, simazine, fenitrothion and tetrachlorvinphos in several soil samples at levels from 5 ng g^?1 to 9 μg g^?1.     

Fragment-molecule adduct ion formation in the mass spectra of cyclic N-acetylamines and related nitramines

Mass spectra of seven related N-heterocyclics, introduced by direct exposure probe, were determined in electron impact (EI) and positive- and negative-ion chemical ionization (PCI and NCI) modes. Proton adducts were the predominant molecular ion species in the EI and PCI modes. In addition, a variety of fragment–molecule adduct ions were observed for each compound in one or more of the modes. The propensity of 1,3,5-trinitrohexahydro-1,3,5-triazine for fragment–molecule adduct formation was high in all three ionization modes. Fragmentation processes were documented by collision-induced dissociation experiments.     

微波辅助萃取-气相色谱-负化学电离/电子轰击电离-飞行时间质谱法测定烟草中农药残留

建立了微波辅助萃取结合气相色谱-飞行时间质谱(GC-TOF MS)技术在负化学电离(NCI)源和电子轰击电离(EI)源两种模式下测定烟草中24种农药残留的分析方法。烟叶样品于100℃下用二氯甲烷-正己烷(3:1, v/v)混合溶剂微波萃取10 min,萃取液经弗罗里硅土固相萃取柱净化后进行检测分析。在NCI源和EI源质谱模式下,24种农药的线性关系均良好(r²>0.99),相对标准偏差分别小于8.6%和9.1%,定量限分别为0.3~6.9 μg/kg和10.2~44.9 μg/kg,加标回收率分别为75.2%~94.8%和75.0%~95.1%。比较两种离子源模式下的色谱图和质谱图,NCI源模式较EI源模式的选择性好、灵敏度高、基质干扰小、图谱简单易于解析,检出限低一个数量级以上,在分析低含量、复杂基质的样品时更具优势。     

气相色谱-电子轰击电离/正化学电离质谱法测定白菜和苹果中3种有机锡类农药残留

分别采用电子轰击电离(EI)源和正化学电离(PCI)源两种离子源技术建立了气相色谱-质谱(GC-MS)同时测定白菜和苹果中苯丁锡、三苯锡和三环锡含量的方法,并对这两种方法进行了比较。样品经氢溴酸消解、丙酮-正己烷(1∶2,v/v)提取,四乙基硼化钠衍生后用Florisil固相萃取柱净化,分别在EI源和PCI源下以选择离子监测模式进行测定。结果表明,方法的检出限(S/N=3)分别为0.01~0.05 mg/kg(EI源)和0.01~0.02 mg/kg(PCI源),定量限(S/N=10)分别为0.03~0.16 mg/kg(EI源)和0.02~0.06 mg/kg(PCI源)。三苯锡、三环锡和苯丁锡分别在各自的线性范围内线性关系良好,相关系数(r~2)≥0.997。在50、100、200μg/kg 3个添加水平下,采用GC-EI/MS和GC-PCI/MS时,阴性样品中3种有机锡的平均回收率分别为59.24%~97.36%(苹果)、50.54%~94.54%(白菜)和65.38%~95.86%(苹果)、62.56%~90.44%(白菜),相对标准偏差(RSD)均不超过6.9%(n=6)。该方法简单、灵敏,PCI源的选择性优于EI源,两种方法可以相互结合提高检测结果的可靠性。     

两种离子化技术气相色谱-质谱法测定橄榄油中甾醇烯类物质的比较

分别采用电子轰击(EI)和正化学电离(PCI)两种离子源技术建立了气相色谱-质谱联用法(GC-MS)同时测定橄榄油中3,5-菜甾二烯、3,5,22-豆甾三烯和3,5-豆甾二烯3种甾醇烯含量的方法,并对这两种方法进行了比较。样品经石油醚溶解,硅胶柱净化后,分别采用GC-EI/MS和GC-PCI/MS分时段选择离子监测模式进行测定,以3,5-胆甾二烯为内标进行定量。结果表明,两种方法的线性、准确度、精密度、灵敏度均较好。3,5-菜甾二烯、3,5,22-豆甾三烯和3,5-豆甾二烯分别在0.024~0.48、0.02~0.50和0.03~0.75 mg/L浓度范围内线性关系良好(r>0.999)。在3个加标水平下,GC-EI/MS和GC-PCI/MS的平均回收率分别为88.7%~99.5%、87.1%~109.2%,两种检测方法的相对标准偏差(RSD,n=6)均不超过8.3%。定量限(S/N=10)分别为0.03 mg/kg(EI),0.03~0.10 mg/kg(PCI)。通过对两种方法的比较研究发现,EI能提供更多碎片离子和结构信息,而PCI中则主要为准分子离子及反应气加合离子。应用于样品中甾醇烯的测定时,PCI的选择性和抗干扰能力明显优于EI。两种方法可相互补充和替代应用于日常检测中。     

Survey of low-level endocrine disrupting pesticides in food matrices in Slovakia

The search on endocrine disrupting chemicals (EDCs) in non-fatty food was evaluated. A fast, high-throughput, accurate, multiresidue method for the analysis of selected EDC pesticides in fruit and vegetable food samples was developed. The QuEChERS technique was used for sample preparation. Fast GC-MS was performed with a narrow-bore capillary column and a quadrupole benchtop detector with electron ionization (EI) and negative chemical ionization (NCI). A part of the work was devoted to the comparison of NCI versus EI approach concerning the sensitivity of detection and to the study of selectivity enhancement in NCI mode. Matrix-matched standard solutions were utilized for calibration. The methods validation was performed. Fortification studies at 1, 5, 10 and 250?µg?kg^?1 for 35 pesticides in EI mode and 0.1, 1, 5 and 250?µg?kg^?1 for 28 pesticides in NCI mode were performed. Average recoveries for each fortification level ranged from 70 to 110% with >80% of recoveries between 90 and 110%. Limits of quantification (LOQs) were established at 5?µg?kg^?1 for EI and at 1?µg?kg^?1 for NCI mode, which is lower than the lowest maximum residue level (MRL) value set by the European Commission in fruit and vegetables. The developed and validated fast GC-MS method was successfully applied to the search of EDC pesticides at ultratrace concentration level in real fruit and vegetable samples in Slovakia. Thirty-four samples of 20 different commodities were analyzed. Seven samples contained residues of three or more EDCs pesticides.     

两种离子源技术气相色谱-质谱法检测茶叶中酰胺类除草剂的残留量

采用电子轰击(EI)和负化学(NCI)离子源两种离子源技术气相色谱-质谱联用法(GC     

Mass spectral fragmentation pathways of N-acetylnitramines: 1-acetylhexahydro-3,5-dinitro-1,3,5-triazine and 1-acetyloctahydro-3,5,7-trinitro-1,3,5,7-tetrazocine

Mass spectra of the N-acetylnitramines l-acetylhexahydro-3,5-dinitro-l,3,5-triazine (TAX) and 1-acetyloctahydro-3,5,7-trinitro-l,3,5,7-tetrazocine (SEX) were recorded in electron impact (EI) and positive and negative chemical ionization (PCI and NCI) modes, and the fragmentation pathways were compared with those of other nitramines which have been well documented and characterized. Unexpectedly, for both acetylnitramines in the EI mode (and in the PCI mode) proton adducts were the only molecular ion species observed; in neither mode was there evidence for higher adducts. In contrast, for TAX in the NCI mode the [M + NO₂]^? adduct was the second most abundant ion (70%); relatively small amounts of the [M + NO]^? adduct (2%) and the hydrogen adduct [MH]^? (3%) were observed. Under identical NCI conditions no molecular ion species or adduct ions were detected for SEX; the ion of highest m/z corresponded to loss of NO₂ or HNO₂ from a molecular ion species. The findings of collision-induced dissociation experiments are also discussed.     

Gas chromatographic and mass spectrometric studies on pyrethroid photo- and biotransformation

Summary Applications of high resolution gas chromatography (GC) and mass spectrometry (MS) in pesticide chemistry are demonstrated by pyrethroid photo- and biotransformation studies. Degradation of chrysanthemate pyrethroids (e.g. the natural pyrethrins, allethrin, tetramethrin and cyphenothrin) used as indoor insecticides is investigated by GC-MS using negative chemical ionization (NCI). Ozonolysis results in the formation of carbox-aldehydes as major indoor transformation products. In vitro metabolism of (S)-bioallethrin and the natural pyrethrins by NADPH dependent oxidases is studied using GC-MS with positive chemical ionization (PCI). Interpretation of the PCI mass spectra yields molecular weight and structural information about the metabolites and their derivatives. The photochemistry of novel non-ester pyrethroids with ether or alkane central linkages such as ethofenprox is investigated by electron impact (EI) GC-MS.     

Analysis of the essential oil from aerial parts of Eupatorium cannabinum subsp. corsicum (L.) by gas chromatography with electron impact and chemical ionization mass spectrometry

Eupatorium cannabinum subsp. corsicum (L.), an aromatic plant, is an endemic subspecies from Corsica. The essential oil from aerial parts of E. cannabinum subsp. corsicum was studied by GC, GC/MS and 13C NMR. One hundred and forty-seven components were identified representing 93.6% of the total amount. The main constituents are germacrene D (28.5%), alpha-phellandrene (19.0%) and para-cymene (5.2%). A particularity of this essential oil is the presence of monoterpene esters derived from nerol, lavandulol, borneol, thymol and 8,9-dehydrothymol. These compounds have been investigated using GC/MS in different ionization modes like electron impact (EI), positive chemical ionization (PCI) and negative chemical ionization (NCI).     

Applications of gas chromatography—mass spectrometry in monitoring environmentally important compounds

The use of gas chromatography-mass spectrometry (GC-MS) with electron impact (EI) and positive and negative chemical ionization (PCI and NCI, respectively) is a valuable confirmatory technique for unequivocal identification of pesticide residues and polychlorinated biphenyls in different environmental matrices. This article outlines some of the most important developments and makes recommendations for selecting the mode of GC-MS operation. Emphasis is placed on less commonly used techniques such as NCI, which provides high selectivity and sensitivity for specific groups of pollutants. The coverage is restricted and represents the personal perspective of the author.     

Integrated system for on-line gas and liquid chromatography with a single mass spectrometric detector for the automated analysis of environmental samples

An integrated system has been developed which combines liquid (LC) and gas (GC) chromatographic separation with a single mass spectrometer (MS). On-line solid-phase extraction (SPE) of 10–200 ml aqueous samples on a short (10 × 2.0 mm I.D.) precolumn packed with a styrene-divinylbenzene copolymer is used for analyte enrichment. The trace-enrichment procedure was automated by means of a PROSPEKT cartridge-exchange/solvent-selection/valve-switching unit. After sample loading, the precolumn is eluted on-line in two subsequent runs, first onto the GC-MS system and, next, onto the LC-MS system using a particle beam (PB) interface. Prior to entering the PB-MS, the LC eluent passes through the flow cell of a UV diode-array detector (DAD). Both GC-MS and LC-PB-MS generate classical electron ionisation (EI) and chemical ionisation (CI) spectra which are useful for the identification of low- and sub-μg/l concentrations of environmental pollutants covering a wide polarity and volatility range. The LC-DAD data provide additional means for quantitation and yield complementary spectral information. All three detection systems (GC-MS, LC-DAD, LC-PB-MS) and the trace-enrichment procedure are fully automated and controlled from the keyboard of the central computer. With such a ‘MULTIANALYSIS’ system GC-MS, LC-DAD and LC-MS data of the same sample can be obtained within 3 h. The system was optimised with nine chlorinated pesticides in drinking water as test mixture. With 100-ml samples detection limits in GC-MS were 0.0005−0.03 μg/l, and in LC-PB-MS 0.5–7 μg/l, both in the full-scan (EI) mode. Negative chemical ionisation (NCI) with methane as reagent gas improved the sensitivity of six halogenated compounds 3- to 30-fold and provided relevant information for structural elucidation of unknown compounds in real-world samples. LC-DAD detection limits varied from 0.01 to 0.05 μg/l. Relative standard deviations (R.S.D.) of retention times were less than 0.2% in all systems, R.S.D.s of peak areas were 5–15% for GC-MS and LC-PB-MS and less than 5% for LC-DAD. The ‘MULTIANALYSIS’ system was used to analyse surface water samples and river sediment extracts; several pollutants were detected and identified.     

Detection and identification of thyreostats in the thyroid gland by gas chromatography-mass spectrometry

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure described herein involves the detection and identification at the low ng g⁻¹ level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatization with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detectable below the 1 ng g⁻¹ level on a quadrupole mass spectrometer with negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of detection was also reached in the SIM high resolution mode. An improved specificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (European Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close to 5 ng g⁻¹ for most thyreostats, which represents a real improvement for their control.     

Development of a headspace GC/MS analysis for carbonyl compounds (aldehydes and ketones) in household products after derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine.

Carbonyl compounds (aldehydes and ketones) are suspected to be among the chemical compounds responsible for Sick Building Syndrome and Multiple Chemical Sensitivities. A headspace gas chromatography/mass spectrometry (GC/MS) analysis for these compounds was developed using derivatization of the compounds into volatile derivatives with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBOA). For GC/MS detection, two ionization modes including electron impact ionization (EI) and negative chemical ionization (NCI) were compared. The NCI mode seemed to be better because of its higher selectivity and sensitivity. This headspace GC/MS (NCI mode) was employed as analysis for aldehydes and ketones in materials (fiber products, adhesives, and printed materials). Formaldehyde was detected in the range of N.D. (not detected) to 39 microg/g; acetaldehyde, N.D. to 4.1 microg/g; propionaldehyde, N.D. to 1.0 microg/g; n-butyraldehyde, N.D. to 0.10 microg/g; and acetone, N.D. to 3.1 microg/g in the samples analyzed.     

Mass spectral fragmentation pathways in some glycoluril-type explosives. A study by collision-induced dissociation and isotope labeling

Electron impact (EI), chemical ionization and negative-ion chemical ionization (NCI) mass spectra of 1,4-dinitroglycoluril (DINGU), its ¹⁵N- and ²H-labeled analogues and the dimethyl-substituted derivatives were recorded. Tandem mass spectrometry with collision induced dissociation was used to study the fragmentation pathways of these compounds. It was found that the main EI fragmentation processes of DINGU are due to the cleavage of C? N bonds and some rearrangement reactions.     

Determination of chlorothalonil in difficult-to-analyse vegetable matrices using various multiresidue methods

The molecular characteristics of chlorothalonil can cause particular determination difficulties in some vegetable commodities such as leek or garlic. These difficulties are mainly related to the low recoveries obtained using common multi-residue methods (MRMs)--a consequence of the very high interaction level with natural components in the matrix. These shortcomings were pointed out in the last European Proficiency Test for Pesticide Residues on Fruits and Vegetables, where false negatives for chlorothalonil in leek were observed at around 50%. In this study we have evaluated the ethyl acetate, the Dutch mini-Luke and the QuEChERS MRMs to compare their capabilities for chlorothalonil determination using GC-MS/MS in both the electron impact ionization (EI) and negative chemical ionization (NCI) modes. Best recoveries (in the range of 100-120%, with an RSD below 20%) were obtained using the Dutch mini-Luke method. Lower values (52-70%) were obtained for ethyl acetate whereas no recovery was obtained when the QuEChERS method was applied. Furthermore, tomato matrix was also included in the experiments in order to facilitate the comparability of results. Two ionization modes, electron impact ionization (EI) and negative chemical ionization (NCI) in GC-MS/MS, were applied to evaluate their respective advantages and disadvantages for quantification and identification. As expected, NCI showed limits of detection (LODs) 5 to 10 times lower than EI. However, in both cases, the LODs were still below 10 μg kg(-1). The proposed optimal method was applied for chlorothalonil determination in leek and garlic with good results--in accordance with the European Union (EU) Analytical Quality Control (AQC) Guidelines for pesticides analysis.     

Determination of eight nitrosamines in water at the ng L levels by liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry

In this work, we have developed a sensitive method for detection and quantification of eight N-nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMor), N-nitrosomethylethylamine (NMEA), N-nitrosopirrolidine (NPyr), N-nitrosodiethylamine (NDEA), N-nitrosopiperidine (NPip), N-nitroso-n-dipropylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) in drinking water. The method is based on liquid chromatography coupled to tandem mass spectrometry, using atmospheric pressure chemical ionization (APCI) in positive mode with a triple quadrupole analyzer (QqQ). The simultaneous acquisition of two MS/MS transitions in selected reaction monitoring mode (SRM) for each compound, together with the evaluation of their relative intensity, allowed the simultaneous quantification and reliable identification in water at ppt levels. Empirical formula of the product ions selected was confirmed by UHPLC-(Q)TOF MS accurate mass measurements from reference standards.Prior to LC–MS/MS QqQ analysis, a preconcentration step by off-line SPE using coconut charcoal EPA 521 cartridges (by passing 500 mL of water sample) was necessary to improve the sensitivity and to meet regulation requirements. For accurate quantification, two isotope labelled nitrosamines (NDMA-d₆ and NDPA-d₁₄) were added as surrogate internal standards to the samples.The optimized method was validated at two concentration levels (10 and 100 ng L⁻¹) in drinking water samples, obtaining satisfactory recoveries (between 90 and 120%) and precision (RSD < 20%). Limits of detection were found to be in the range of 1–8 ng L⁻¹. The described methodology has been applied to different types of water samples: chlorinated from drinking water and wastewater treatment plants (DWTP and WWTP, respectively), wastewaters subjected to ozonation and tap waters.     

两种离子源技术GC/MS法检测蔬菜中多类除草剂的残留量

采用电子轰击(EI)和负化学(NCI)离子源两种离子源技术气相色谱-质谱联用法(GC-MS)测定了蔬菜中10类除草剂的残留量, 并对两种方法进行了比较. 样品经乙腈提取后, 用PSA固相萃取柱净化, 由气相色谱-质谱联用EI或NCI技术进行定量和定性分析. 对含电负性强的除草剂分析, NCI灵敏度高, 在10 ng/g, 20 ng/g和40 ng/g 3个添加水平下的方法回收率为70%～115%, RSD为1.7%～10.1%, 两种离子源技术可以互相补充用于准确检测蔬菜中多类除草剂.     

Comparison of high resolution gas chromatography with electron impact and negative ion mass spectrometry detection for the determination of coplanar polychlorobiphenyl congeners in sewage sludges

The three most toxic coplanar PCB 77, 126 and 169 have been identified and quantified at ultra trace levels (0.02–4.8 ng/gdw) in swiss sewage sludge samples applying high resolution capillary gas chromatography (HRGC) and electron impact (EI) as well as negative ion chemical ionization (NCI) mass spectrometry (MS). NCI mass spectra have been dominated by the molecular ion as base peak and virtually no fragmentation has been observed. Detection limits of the planar PCB under single ion monitoring (SIM) conditions have been typically 100 fg for NCI-MS and 1 pg for EI-MS. NCI-MS was the preferred detection method for the determination of very low concentrations of these important contaminants in sewage sludge samples.     

Performance of gas chromatography/tandem mass spectrometry in the analysis of pyrethroid insecticides in environmental and food samples

The performance of gas chromatography coupled with tandem mass spectrometry (GC/MS/MS) was tested for the simultaneous determination of twelve pyrethroid insecticides. First, a comparison of two different ionization modes, electron ionization (EI) and negative chemical ionization (NCI), was carried out using MS and MS/MS. NCI-MS/MS provided the best results in terms of selectivity and sensitivity giving very low detection limits of 0.11 to 450 fg injected. The reliability of the method was confirmed through the evaluation of quality parameters such as accuracy (70-100%), and repeatability and reproducibility, with coefficients of variation below 15% and 10%, respectively. The applicability of the GC/MS/MS method to real samples and influence of matrix effects were evaluated through the analysis of spiked water, sediment and milk at 0.25 ng L(-1) , 5 ng g(-1) dry weight (dw) and 25 ng g(-1) (dw), respectively, of each pyrethroid insecticide considered. Using GC/NCI-MS/MS, matrix spectral interferences were minimized providing method limits of detection (MLODs) of 0.05-2.59 ng L(-1) , 0.10-87.7 pg g(-1) dw, 2.29-1071 pg g(-1) lipid weight (lw) for water, sediment and milk, respectively. To the best of our knowledge, the MLOD values found in our study were better than those reported in previous studies; in particular for sediment and food samples, they were one order of magnitude lower.