Reliable identification of pesticides using linear retention indices as an active tool in gas chromatographic-mass spectrometric analysis

The present research is focused on the current development and employment of a dedicated pesticide mass spectral library, characterized by a double-filter search procedure: the first is based on the degree of spectral similarity and the second on chromatographic retention information (linear retention indices). The highly pure mass spectra contained in the library have been attained by subjecting mixtures of widely used pesticides to comprehensive GC-MS analysis. Linear retention indices for conventional GC-MS analyses were calculated by injecting the same compounds on a single-column GC-MS system. The effectiveness of this approach was verified by analysing a white wine sample spiked with 10 structurally similar pyrethroid compounds, through automated solid-phase microextraction-GC-MS.     

Phenolics in selected European hardwood species by liquid chromatography-electrospray ionisation mass spectrometry

The phenols in beech (Fagus sylvatica), birch (Betula pendula) and ash (Fraxinus excelsior) wood dusts were compared using a mass spectrometer fitted with an electrospray ionisation interface with liquid chromatographic separation. Hardwood dust is a carcinogen, and an analysis of the polyphenol profile is a useful method for identifying the dust source in workplace air. The mass spectrometer was operated in both the negative and positive ion modes. Phenolic compounds were identified by comparing mass spectra and retention times from liquid chromatography with those for standard compounds and data in the literature. The phenol contents of the studied wood species varied considerably, and only a few common compounds were found in them.     

气相色谱QSRR研究在质谱谱库检索定性中的应用

对质谱谱图相似的多取代烷基苯各位置异构体,根据一种从苯、单取代烷基苯及双取代烷基苯保留指数预测相关多取代烷基苯保留指数的方法,测定了基础化合物在OV－1毛细管柱上的保留指数,预测了相关多取代烷基苯在OV－1上的保留指数。利用该保留数据,结合质谱,给予了正确定性,从而解决了质谱谱库检索定性时对于各位置异构体难于定性的困难。     

Software improvements for gas chromatography-mass spectrometry-calculator system used in the analysis of trace organic compounds from environmenta samples

Computer programs are described which have significantly increased the capabilities of a low-cost gas chromatogaphy-mass spectrometry (GC-MS)-calculator system. These programs allow storage on floppy disk of ion abundance and retention time data for the total ion current and as many as six mass chromatograms in addition to mass spectra taken at the top of eluting GC peaks. Manufacturer-supplied software was only capable of storing the mass spectra. Ion abundance data may be displayed by means of a flexible, interactive program which uses an x–y plotter. Both qualitative and quantitative analyses may be performed for selected compounds in a single GC-MS run. Examples of the use of this software in the analysis of benzene extracts of incinerator fly-ash samples are presented.     

Comprehensive two-dimensional gas chromatography for fingerprint pattern recognition in cachaça production

Cacha?a samples were studied by means of comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (GCxGC/TOFMS) during the fermentation process and after ageing in different wood materials. The analyses of the aroma compounds were performed after headspace-solid phase microextraction method (HS-SPME) using an 85microm polyacrylate (PA) fibre. Fingerprint monitoring of the distillation process allowed the easy determination of the turning points of the process and high-resolution comparison of cabe?a (head), cora??o (core) and cauda (tail) fractions. The ageing process in different wood materials was well characterised through fingerprint similarity observations; in the absence of a suitable metric for expressing the overall similarity, here we use a visual and retention time comparison to identify co-incident peaks and those that differ between samples. For quality control purposes, a simple observation of the contour plots obtained can thus allow the identification of the type of wood used in the ageing process, and the process of ageing, without further statistical treatment or peak identifications. In this manner, peaks, which discriminated most between the different mixtures studied were readily found, i.e. unique compounds were identified in each stage of the distillation process. Approximate first dimension linear retention indices (LRI) for these identified compounds were calculated in a bi-dimensional polar/non-polar column set in the GCxGC experiment and were used in conjunction with mass spectral library searching for tentative identification. Along the progression of the distillation process, 70 compounds appear to visually discriminate between samples and their retention indices are indicated, presenting good correlation with literature data.     

Tracing of surfactants in the biological wastewater treatment process and the identification of their metabolites by flow injection-mass spectrometry and liquid chromatography-mass spectrometry and -tandem mass spectrometry

Results of aerobic biodegradation of alkyl ethoxylates (AEOs), of nonylphenol polyethoxylates (NPEOs), and of NPEO derivatives (sulfonates and sulfates), as well as anaerobic NPEO biodegradation monitored by flow injection analysis (FIA) or liquid chromatographic separation (LC) in combination with mass (MS) and tandem mass spectrometry (MS-MS) are presented. The application of visual pattern recognition in the FIA-MS mode showed quite different degradation pathways for C13-AEOs, so that aldehyde compounds as metabolites could be confirmed by collision-induced dissociation for the first time. Methyl ethers of AEO compounds were found to be persistent under aerobic conditions, while NPEO degradation resulted in nonylphenol polyether carboxylates. FIA- and LC-MS proved that NPEO derivatives used as anionic surfactants were either non-biodegradable (nonylphenol diethoxy sulfonate) or were primarily degraded (nonylphenol polyethoxy sulfates) into compounds of the same molar masses yet of different retention behaviour. Anaerobic degradation of NPEOs led to the generation of nonylphenols, which was confirmed by GC-MS.     

Comparison of two methods of measuring wood pyrolysis tar

Two methods for the sampling and analysis of tar produced from wood pyrolysis were compared. The first method used a conventional cold-trapping technique in solvent-filled impingers followed by liquid injection. The second one is a new application of multibed solid-phase adsorbent (SPA) tubes followed by thermal desorption (TD). Both methods are based on gas chromatography (GC) coupled with mass spectrometry (MS). Quantification was performed with a well reproducible GC-MS method with three internal deuterated standards. The SPA/TD method offers several advantages. No solvent is required, the detection levels are improved, and gas chromatography separation is easier. Moreover, sampling time is reduced from about 1h (for the conventional cold-trapping technique in impingers) to a few seconds. No discrimination was observed between the two sampling methods for the 10 quantified compounds (aromatic compounds from benzene to phenanthrene and phenols) except for benzene.     

Classification of high-speed gas chromatography-mass spectrometry data by principal component analysis coupled with piecewise alignment and feature selection

A useful methodology is introduced for the analysis of data obtained via gas chromatography with mass spectrometry (GC-MS) utilizing a complete mass spectrum at each retention time interval in which a mass spectrum was collected. Principal component analysis (PCA) with preprocessing by both piecewise retention time alignment and analysis of variance (ANOVA) feature selection is applied to all mass channels collected. The methodology involves concatenating all concurrently measured individual m/z chromatograms from m/z 20 to 120 for each GC-MS separation into a row vector. All of the sample row vectors are incorporated into a matrix where each row is a sample vector. This matrix is piecewise aligned and reduced by ANOVA feature selection. Application of the preprocessing steps (retention time alignment and feature selection) to all mass channels collected during the chromatographic separation allows considerably more selective chemical information to be incorporated in the PCA classification, and is the primary novelty of the report. This methodology is objective and requires no knowledge of the specific analytes of interest, as in selective ion monitoring (SIM), and does not restrict the mass spectral data used, as in both SIM and total ion current (TIC) methods. Significantly, the methodology allows for the classification of data with low resolution in the chromatographic dimension because of the added selectivity from the complete mass spectral dimension. This allows for the successful classification of data over significantly decreased chromatographic separation times, since high-speed separations can be employed. The methodology is demonstrated through the analysis of a set of four differing gasoline samples that serve as model complex samples. For comparison, the gasoline samples are analyzed by GC-MS over both 10-min and 10-s separation times. The successfully classified 10-min GC-MS TIC data served as the benchmark analysis to compare to the 10-s data. When only alignment and feature selection was applied to the 10-s gasoline separations using GC-MS TIC data, PCA failed. PCA was successful for 10-s gasoline separations when the methodology was applied with all the m/z information. With ANOVA feature selection, chromatographic regions with Fisher ratios greater than 1500 were retained in a new matrix and subjected to PCA yielding successful classification for the 10-s separations.     

气相色谱-质谱测定环境样品的质量控制与质量保证

以环境样品分析为例,指出了气相色谱-质谱技术分析测定过程的质量控制的主要因素及措施,并从内标物、替代品、进样系统、色谱柱、质谱运行状态、保留时间、标准曲线、仪器软件系统等方面对如何提高分析过程的准确度进行了讨论。     

固相萃取-气相色谱-质谱法测定木制家具中氯酚类及菊酯类防腐剂

建立了固相萃取-气相色谱-质谱(SPE-GC-MS)检测含氯酚类化合物(2,4-二氯苯酚、2,4,6-三氯苯酚、2,4,5-三氯苯酚、2,3,4,6-四氯苯酚、五氯苯酚、林丹)和菊酯类化合物(氯菊酯、氟氯氰菊酯、氯氰菊酯、溴氰菊酯)等10种木材防腐剂的方法。对家具样品采用超声萃取法、以甲醇为提取剂在室温下反复提取2次,提取液经浓缩后,加入碳酸钾和乙酰酐衍生化,将衍生化后的溶液通过Oasis HLB固相萃取柱净化,用乙酸乙酯洗脱并收集检测。采用该方法实现了家具中10种木材防腐剂的分离检测,该方法中氯酚类防腐剂定量限为1 mg/kg、菊酯类防腐剂定量限为5 mg/kg,平均回收率为76.0%～108.8%。应用该方法对市场上销售的木制家具进行了检测,在部分家具中检出含有少量林丹。实验结果证明,该方法准确、灵敏,可有效地应用于木制家具中防腐剂的实际检验工作中。     

Derivatization of pinacolyl alcohol with phenyldimethylchlorosilane for enhanced detection by gas chromatography–mass spectrometry

A derivatization procedure for the qualitative gas chromatography–mass spectrometry (GC-MS) analysis of pinacolyl alcohol (PA) that employs phenyldimethylchlorosilane (PhDMClS) and the promoter N-methylimidazole is described. While PA, underivatized, can be detected using conventional gas chromatographic methods, its polarity and low boiling point make its detection in complex matrices challenging. The silylation procedure described herein generates a PA-derivative exhibiting an increased on-column retention time, thus shifting its GC-MS signal away from commonly encountered, volatile, interfering analytes. Derivatized PA could be distinguished from other PhDMClS-derivatized isomeric alcohols by its unique retention time and mass spectrum. The derivatization was demonstrated to perform well in the GC-MS analysis and identification of PA in samples from Proficiency Tests administered by the Organisation for the Prohibition of Chemical Weapons (OPCW).

Discrimination of structural isomers of chlorinated phenols in waters using gas chromatography-mass spectrometry in the negative chemical ionization mode

The analysis and identification of structural isomers of mono-, di- and trichlorophenols is reported. The fragmentation of the phenols was examined by GC-MS in both electron impact (EI) and negative chemical ionization (NCI) modes, using methane as reagent gas. The ability of NCI to discriminate these isomeric compounds from differences in relative intensities for selected peaks is demonstrated. 3- and 4-chlorophenols have similar retention times; however, they can still be discriminated because their negative mass spectra and rather different. In dichlorophenols, the presence of one chlorine atom in the ortho position decreases their retention time and the relative intensity of the fragment ion at m/z 140. The NCI mass spectra for trichlorophenols are different from the rest, particularly for the m/z value corresponding to the chlorine atom. Tetra- and pentachlorophenols were also studied and sequential losses of Cl observed. An automatic solid-phase extraction system can optionally be used to preconcentrate chlorophenols in waters prior to determination at legally established toxic levels.     

Analysis of the chemical composition of the essential oil of Polygonum minus Huds. using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC-TOF MS)

The essential oil in leaves of Polygonum minus Huds., a local aromatic plant, were identified by a pipeline of gas chromatography (GC) techniques coupled with mass-spectrometry (MS), flame ionization detector (FID) and two dimensional gas chromatography time of flight mass spectrometry (GC x GC-TOF MS). A total of 48 compounds with a good match and high probability values were identified using this technique. Meanwhile, 42 compounds were successfully identified in this study using GC-MS, a significantly larger number than in previous studies. GC-FID was used in determining the retention indices of chemical components in P. minus essential oil. The result also showed the efficiency and reliability were greatly improved when chemometric methods and retention indices were used in identification and quantification of chemical components in plant essential oil.     

Novel gas chromatography-mass spectrometry database for automatic identification and quantification of micropollutants

A novel gas chromatography-mass spectroscopy (GC-MS) database for identification and quantification of micropollutants in environmental and food samples is reported. GC retention times, calibration curves, and mass spectra of nearly 700 chemicals were registered in the database, and the GC retention times of registered chemicals in actual samples were predicted from the retention times of n-alkanes measured before sample analysis. Differences between predicted and actual retention times were less than 3 s, an accuracy that is nearly identical to that obtained by analysis of standard substances. After the retention times were predicted, a calibration file for the GC-MS instrument was created from the predicted retention times, calibration curves, and mass spectra of the registered chemicals. With the resulting calibration file, automated identification of all the chemicals in actual samples was possible without the use of standards, and the identification method was as reliable as conventional methods. When the GC inlet, column, and tuning conditions were adjusted using GC-MS performance check standards, relative standard deviations of 20% or less for determination values could be obtained. More than 90% of the chemicals in the database could be detected at a sensitivity sufficient for all practical purposes (100 pg or less). Because each chemical in the database, to which new substances can easily be added, can be determined in 1 h, micropollutants in samples can be analyzed efficiently and inexpensively.     

Determination of Essential Oil Components of Star Anise (Illicium verum) Using Simultaneous Hydrodistillation–Static Headspace Liquid-Phase Microextraction–Gas Chromatography Mass Spectrometry

Abstract

In this study, the hydrodistillation–headspace solvent microextraction (HD-HSME) method was used for extraction and analysis of chemical components of star anise (Illicium verum). Effective parameters for HSME, such as the nature of the extracting solvent, headspace volume, particle size of the sample, and the extraction time, were studied and optimized, and the method's performance was evaluated. The chemical compositions of the HD-HSME and HD extracts were confirmed according to their retention indexes and mass spectra (EI, 70 eV), and quantitative analysis was performed by gas chromatography (GC)–flame ionization detection (FID). Using HD-HSME followed by GC-MS, 49 compounds were separated and identified in star anise, which mainly included trans-anethole (81.4.0%), limonene (6.50%), chavicol (2.10%), and anisaldehyde (1.81%). The results of HD-HSME followed by GC-MS, in comparison with traditional the hydrodistillation method, shows that the proposed method is simple, rapid, and efficient for the determination of volatile compounds in star anise.     

固相微萃取-气相色谱-质谱联用结合嗅觉检测法鉴定血橙汁中的香气活性化合物

采用固相微萃取-气相色谱-质谱法(SPME-GC-MS)和嗅觉检测法对血橙汁中的挥发性物质进行分析,确定了血橙汁中的香气活性化合物。采用二乙烯基苯/碳分子筛/聚二甲基硅氧烷共聚物(DVB/CAR/PDMS)萃取头在40 ℃条件下顶空萃取40 min。通过气相色谱-质谱联用结合保留指数,在所萃取的血橙汁的挥发性化合物中共鉴定出46种化合物。通过嗅觉检测法检测出34种具有气味的化合物,其中23种被定性。结果表明,对血橙汁香气起主要贡献的化合物是丁酸乙酯、辛醛、γ-松油烯、芳樟醇、4-乙酰基-1-甲基环己烯、癸醛、(-)-香芹酮、乙酸香叶酯、巴伦西亚桔烯以及保留指数分别为1020,1143,1169和小于800的4个未知化合物,这些香气强度较高的化合物的总相对含量为7.22%。     

Comparison of volatile components in Chinese traditional pickled peppers using HS-SPME-GC-MS, GC-O and multivariate analysis

Volatile compounds of Chinese traditional pickled peppers (CTPPs) were extracted by solid-phase micro-extraction (SPME) and analysed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) to visually compare their volatile compositions by applying principal component analysis (PCA). A total of 67 volatile components were identified by GC-MS, including 7 acids, 6 alkanes, 14 alcohols, 9 esters, 11 terpenes, 3 aldehydes, 5 ketones, 7 phenols and 5 miscellaneous compounds, tentatively identified or identified by comparing with mass spectra and retention indices of the standards or from literature. Of 45 volatile compounds detected in the sniffing port of GC-O, the majority of odour-active components included acetic acid, 2-ethyl phenol, L-linalool, tridecane, butyl butanoate, δ-3-carene. The individual concentrations of the volatile compounds such as acetic acid, ethanol, 1-propanol, L-linalool, hexyl 2-methyl butyrate and hexyl pentanoate corresponded well to the intensities of related attributes in the correlation analysis. Due to their high concentration level and low threshold value, these compounds played an important role in the final aromatic profile of the pickled peppers. The differences in flavours were observed by applying PCA to GC-MS data sets. From the PCA results, samples were primarily separated along the first principal component.     

气相色谱-四极杆高分辨飞行时间质谱分析复杂芳烃体系中的苯甲醛、苯甲醇、苯乙酮与苯乙醛

建立了气相色谱-四极杆高分辨飞行时间串联质谱分析复杂芳烃体系样品中苯甲醛、苯甲醇、苯乙酮与苯乙醛的方法。该方法通过使用高分辨质谱得到目标化合物特征离子的精确质量数,结合色谱保留时间,有效排除了复杂芳烃体系样品本底中碎片离子的干扰,提高了定性与定量分析的准确性。使用目标化合物特征离子的质谱峰面积作为定量计算依据。苯甲醛、苯甲醇、苯乙酮与苯乙醛在各自的质量浓度范围内呈现良好的线性响应,回收率为87.97%~103.01%,定量限分别为0.04、0.10、0.08与0.03 mg/L,检出限分别为0.01、0.03、0.02与0.01 mg/L。对3份实际样品中的苯甲醛、苯甲醇、苯乙酮与苯乙醛进行了定量分析。本研究为气相色谱-四极杆高分辨飞行时间质谱技术应用于复杂体系中的微量杂质分析提供了一种新的思路和手段。通过精确的质量分辨和测定可以降低对色谱分离的依赖,弥补传统气相色谱-四极杆低分辨质谱技术的不足。     

Application of gas chromatography - field asymmetric ion mobility spectrometry (GC-FAIMS) for the detection of organic preservatives in wood

The purpose of the investigations reported was a feasibility study of field asymmetric ion mobility spectrometry (FAIMS) applications for the characterization of recovered wood. Especially the treatment with organic wood preservatives represented by their active substances should be detected in concentrations commonly used for timber products. The following pesticides were determined: PCP, lindane, dichlofluanide, tolylfluanide, propiconazole, tebuconazole, IPBC (iodine-propyl-butyl-carbamate), K-HDO ((N-Cyclohexyl-diazeniumdioxy)-potassium) and fenoxycarb. The first step was to show that such compounds can be vaporized under moderate conditions. Solid-phase microextraction (SPME) was capable for sampling and enrichment. The reference analytics was made by gas chromatography coupled with mass spectrometry (GC-MS). Both, waste wood, in this case window frames from reconstruction work, and self-prepared doped wood samples were utilized. For analyzing the complex mixture of vaporized native and artificial ingredients of the lignocellulose material a chromatographic pre-separation was necessary. Hence, the second step was to study the behavior of active substances in the analysis with GC-FAIMS to clarify which peaks in positive and negative mode are dedicated to wood preservatives. At least one strong signal from every selected active compound was located for clear identification. With that knowledge, FAIMS was successfully applied for the distinction of natural and treated wood samples. The discrimination can be a basis for industrial sorting plants which could help to increase the contemporary amount of material usage of recovered wood for a more ecological and economical handling of natural resources.     

Characterization of archaeological frankincense by gas chromatography-mass spectrometry

A simple gas chromatography-mass spectrometry (GC-MS) method has been developed for the characterization of frankincense in archaeological samples. After trimethylsilylation of the methanolic extract, 15 triterpenoids have been found among the chemical constituents of commercial olibanum (alpha-boswellic acid, 3-O-acetyl-alpha-boswellic acid, beta-boswellic acid, 3-O-acetyl-beta-boswellic acid, alpha-amyrin, beta-amyrin, lupeol, 3-epi-beta-amyrin, 3-epi-beta-amyrin, 3-epi-lupeol, alpha-amyrenone, beta-amyrenone, lupenone, 3alpha-hydroxy-lup-20(29)-en-24-oic acid and 3-O-acetyl-hydroxy-lup-20(29)-en-24-oic acid). These compounds have been unequivocally identified by retention time and mass spectral comparison with pure standards previously isolated, for the most part, in our laboratory. Within these triterpenes, acid ones, the corresponding O-acetates, and their products of degradation were found to be characteristic of frankincense (Boswellia resin). The presence of these unusual triterpenic compounds in an archaeological resinous sample, recovered during excavations from Dahshour site (Egypt, XIIth Dynasty), enabled us to identify unambiguously frankincense resin among several other materials. Additional chromatographic peaks of this sample were assigned to broad chemical classes using retention time and mass spectra features.