Comparison of differential mobility spectrometry and mass spectrometry for gas chromatographic detection of ignitable liquids from fire debris using projected difference resolution

The significance of forensic arson analysis accelerates the applications of new technologies in this area. Based on the previously reported application of differential mobility spectrometry (DMS) as a detection method for gas chromatography (GC) in arson analysis, the performances of DMS and mass spectrometry (MS) were compared using a novel chemometric tool, projected difference resolutions (PDRs). The PDR results show that one-way mass spectra data exhibit higher resolution than DMS data, while total ion chromatograms from GC–DMS show higher resolution than that from GC/MS for differentiating seven kinds of ignitable liquids. Combining the information from both chromatography and spectra, two-way data always have higher resolution than one-way data for these two detection methods, and GC/MS would exhibit better performance than GC–DMS according to the minimum resolution value. To verify the PDR results, a fuzzy rule-building expert system was applied for classifying these seven kinds of ignitable liquids from fire debris based on GC–DMS and GC/MS data, respectively. The prediction accuracies were consistent with PDR results, which proved that PDR is a powerful tool in comparing the performances of different analysis methods for pattern recognition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Chemometric analysis of diesel fuel for forensic and environmental applications

Diesel fuel samples were analyzed using gas chromatography-mass spectrometry (GC-MS) and chemometric procedures to associate and discriminate samples for potential use in forensic and environmental applications. Twenty-five diesel samples, representing 13 different brands, were collected from service stations in the Lansing, Michigan area. From the GC-MS data, mass-to-charge ratios were identified to represent aliphatic (m/z 57) and aromatic (m/z 91 and 141) compounds. The total ion chromatogram (TIC) and extracted ion chromatograms (EICs) of the chosen ions were evaluated using Pearson product moment correlation (PPMC) and principal component analysis (PCA). Diesel samples from the same brand showed higher PPMC coefficients, while those from different brands showed lower values. EICs generally provided a wider range of correlation coefficients than the TIC, with correspondingly increased discrimination among samples for EIC m/z 91. PCA grouped the diesel samples into four distinct clusters for the TIC. The first cluster consisted of four samples from the same brand, two clusters contained one diesel sample each of different brands, and the fourth cluster contained the remaining diesel samples. The same trend was observed using each EIC, with an increase in the number of clusters formed for EIC m/z 57 and 91. Both statistical procedures suggest aromatic components (specifically, those with m/z 91) provide the greatest discrimination among diesel samples. This conclusion was supported by identifying the chemical components that contribute the most to the variance. The relative amount of aliphatic versus aromatic components was found to cause the greatest discrimination among samples in the data set.     

Simultaneous analysis of fourteen tertiary amine stimulants in human urine for doping control purposes by liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry

A method for the simultaneous screening and confirmation of the presence of fourteen tertiary amine stimulants in human urine by gas chromatography-mass spectrometry (GC-MS) in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed and validated. Solid phase extraction (SPE) and liquid-liquid extraction (LLE) approaches were utilized for the pre-treatment of the urine samples. The study indicated that the capillary temperature played a significant role in the signal abundances of the protonated molecules of cropropamide and crotethamide under positive ion electrospray ionization (ESI) conditions. In addition, comparison studies of two different pre-treatment approaches as well as the two ionization modes were conducted. The LODs of the developed method for all the analytes were lower than the minimum required performance limit (MRPL) as set forth in the World Anti-Doping Agency (WADA) technical document for laboratories. The human urine sample obtained after oral administration of prolintane·HCl was successfully analyzed by the developed method, which demonstrated the applicability and reliability of the method for routine doping control analysis.     

A simple,inexpensive, rapid,sensitive and solventless technique for the analysis of accelerants in fire debris based on SPME

The current method of choice for the extraction of flammable or combustible liquid resides from fire debris samples is passive headspace concentration using activated charcoal strips (ACS) for adsorption of the liquid residues followed by elution with carbon disulfide or other suitable solvent. Presently, we report a new technique based on headspace solid-phase microextraction which has been successfully applied to the identification of a wide range of accelerants commonly seen in arson analysis. The SPME technique developed is simple, inexpensive, rapid, and eliminates the use of the highly flammable and toxic solvent carbon disulfide. Results using this SPME method have been directly compared to results obtained via the ACS technique for light, medium, and heavy petroleum distillates as well as gasoline. All of the accelerants studied were accurately identified by the SPME method with equal or greater sensitivity compared to the ACS method.     

广西产湿地松松针挥发性成分的提取及分析

采用水蒸气蒸馏法提取湿地松针叶挥发油的油相部分,用乙醚萃取法提取蒸馏残液中的水溶性挥发性组分,利用气相色谱-质谱联用分析比较二者的化学成分。湿地松挥发油油相部分的得油率为0.277%,共分离出86个色谱峰,鉴定了其中的49种化合物,占总含量的92.12%,油相部分的主要成分有β-蒎烯（14.29%）、吉马烯（12.87%）、α-蒎烯（6.79%）、β-石竹烯（6.15%）、α-石竹烯（1.58%）;水溶性部分的得油率为0.0682%,鉴定了其中的6种化合物,占水溶性部分总量的60.72%,α-松油醇（24.61%）为水溶性部分的主要成分。由于增加了水溶部分精油的提取,湿地松松针挥发油总的产油率提高到0.3452%,提高率达24.62%。     

Characterization of the aromatic profile for the authentication and differentiation of typical Italian dry-sausages

In order to chacterize two kinds of typical Italian dry-sausages, namely “Salame Mantovano” and “Salame Cremonese”, the volatile composition was determined for seven samples of “Salame Mantovano” and for five samples of “Salame Cremonese”. The study was performed by the dynamic headspace extraction technique (DHS) coupled with gas chromatography-mass spectrometry (GC-MS). Among the 104 volatiles identified, terpenes, aldehydes, ketones and alcohols represented the most abundant compounds. Peak area data for all the substances from the above mentioned group was used for statistical purposes. Firstly, principal component analysis (PCA) was carried out in order to visualize data trends and to detect possible clusters within samples. Then, linear discriminant analysis (LDA) was performed in order to detect the volatile compounds able to differentiate the two kinds of sausages investigated. The data obtained by GC-MS shows that the most important contributions to the differentiation of the two kinds of typical Italian salami were seven volatile compounds, i.e. 3-methylbutanal, 6-camphenol, dimethyl disulfide, 1-propene-3,3′-thiobis, ethyl propanoate, 1,4-p-menthadiene and 2,6-dimethyl-1,3,5,7-octatetraene. Prediction ability of the calculated model was estimated to be 100% by the “leave-one-out” cross-validation.     

General unknown screening procedure for the characterization of human drug metabolites in forensic toxicology: Applications and constraints

LC coupled to single (LC–MS) and tandem (LC–MS/MS) mass spectrometry is recognized as the most powerful analytical tools for metabolic studies in drug discovery. In this article, we describe five cases illustrating the utility of screening xenobiotic metabolites in routine analysis of forensic samples using LC–MS/MS. Analyses were performed using a previously published LC–MS/MS general unknown screening (GUS) procedure developed using a hybrid linear IT–tandem mass spectrometer. In each of the cases presented, the presence of metabolites of xenobiotics was suspected after analyzing urine samples. In two cases, the parent drug was also detected and the metabolites were merely useful to confirm drug intake, but in three other cases, metabolite detection was of actual forensic interest. The presented results indicate that: (i) the GUS procedure developed is useful to detect a large variety of drug metabolites, which would have been hardly detected using targeted methods in the context of clinical or forensic toxicology; (ii) metabolite structure can generally be inferred from their “enhanced” product ion scan spectra; and (iii) structure confirmation can be achieved through in vitro metabolic experiments or through the analysis of urine samples from individuals taking the parent drug.     

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.     

Determination of VOC and TVOC in Air Using Thermal Desorption GC-MS – Practical Implications for Test Chamber Experiments

The determination of volatile organic compounds (VOC) species and concentrations are important for the evaluation of indoor air quality. Numerous methods exist for the determination of levels of both VOC and TVOC (total volatile organic compounds). These include the use of direct-reading instruments as well as gas chromatographic techniques. The benefits and drawbacks of the various methods are well known, and none provide precise measurement of the complex VOC mixtures that constitute TVOC in indoor air. A specific approach for TVOC measurement has been proposed in Europe in ECA-report no.19 to overcome these shortcomings. On this basis a practical analytical method was developed and applied to emission test chamber studies. Special focus was required on compounds of high volatility and the preparation of calibration standards.     

马尾松和湿地松松针挥发性成分的提取及GC-MS比较分析

采用水蒸气蒸馏法提取马尾松和湿地松松针叶挥发油的油相部分,用乙醚萃取法提取蒸馏残液中的水溶性挥发性组分,利用气相色谱-质谱联用分析比较它们的化学成分。由于增加了水溶性部分的提取,马尾松和湿地松挥发油总的得油率提高到0.4709%和0.3452%,提高率分别达19.17%和24.62%。马尾松挥发油的油相成分和水溶性成分组成部分相同,但含量相差较大;而湿地松针叶精油的油相和水相部分成分组成差别较大;马尾松和湿地松相比较,针叶精油（油相部分）的主要化学成分大致相同,都是以单萜和倍半萜为主,但在含量上有较大差别。     

Detection and use of selective ions for providing initial estimates of the concentration vectors in iterative target transformation factor analysis

The characteristic of discreteness in mass spectral direction distinguishes GC/MS from other spectral techniques. Based on this feature, we propose a new method to construct the initial concentration vectors for iterative target transformation factor analysis (ITTFA). For each chemical component, a search for a selective ion with good signal-to-noise ratio is first conducted using evolving factor analysis (EFA) and information entropy. The corresponding chromatogram of the selective ion is subsequently applied to construct an initial concentration vector for ITTFA. Special strategies are developed to cope with chromatographic patterns with embedded peaks and complex multicomponent structure. Results from three simulated and one real mixture and comparison with results from heuristic evolving latent projections (HELP) and a previously published method for definition of the initial profiles for ITTFA, indicate that selective ion chromatogram (SIC) ITTFA represents a fast, automatic and accurate method for resolution of GC/MS data.     

超临界CO2流体萃取法与水蒸气蒸馏法提取荆芥穗挥发油化学成分的研究

采用超临界CO2萃取法(SFE)与水蒸气蒸馏法(SD)从荆芥穗中提取挥发油。采用SE-54毛细管柱进行分析,用气相色谱-质谱法对挥发油中各种化学成分进行鉴定,用归一化法测定各组分的含量。色谱条件:SE-54毛细管柱 (30 m×0.25 mm i.d.,0.25 μm),柱温50 ℃(3 min)5 ℃/min180 ℃(2 min)10 ℃/min260 ℃(50 min);分流进样,分流比1∶50;进样口温度280 ℃。在采用超临界CO2萃取法提取的挥发油中共鉴定出54种成分,其主要成分为长叶薄荷酮、薄荷酮、亚油酸氯化物等;在水蒸气蒸馏法提取的挥发油中共鉴定出39种成分,其主要成分为长叶薄荷酮、薄荷酮、柠檬烯等。超临界法较水蒸气法更加稳定可靠,重现性好,适用于中药挥发油的化学成分分析。     

Standards and GC-MS analysis: An answer to the requirement of compound confirmation

Summary The attribution of an unknown GC-MS chromatographic peak to a specific substance should be confirmed whenever possible by comparison with a standard compound analysed under the same experimental conditions. The range of chemicals supplied by various companies is very wide but can never be completely comprehensive. This paper proposes two simple ways by which a reference compound may be obtained. Firstly, it may occur as an impurity in a commercial sample as a synthesis by-product. Alternatively, the compound may be synthesized by a simple procedure, preferably a single step one, by putting small amounts of reagents in a sealed glass vial placed in a programmable oven. Examples of these two approaches are described.     

Development of a simultaneous pressurised-liquid extraction and clean-up procedure for the determination of UV filters in sediments

A useful tool for the determination of eight UV filters in sediments which combines extraction and clean-up in a single-step has been developed. To this end, the protocol incorporates silica gel and copper powder placed directly in the pressurised-liquid extraction (PLE) cell. After extract evaporation, salicylate- and benzophenone-type UV filters are derivatised with N,O-bis-trimethylsilyltrifluoroacetamide (BSTFA). Trimethylsilylation increases the sensitivity of these UV filters about 4-10-fold when they are finally analysed by gas chromatography-mass spectrometry (GC-MS). Derivatisation conditions (temperature, time and volume of BSTFA) and PLE parameters (temperature, time, number of cycles and solvent composition) were optimised using multivariate experimental designs. Under optimal conditions, the developed procedure provides an excellent linearity, detection limits (1-5 ng g⁻¹) and recoveries above 73% for all the compounds. Compared to the few existing methods, this analytical approach affords optimal throughput and method automation. Finally, the proposed method was applied to the analysis of three sediment samples.     

Analytical Method Development for the Simultaneous Determination of Five Human Pharmaceuticals in Water and Wastewater Samples by Gas Chromatography-Mass Spectrometry

Summary Effective analytical methods for the simultaneous determination of five pharmaceuticals from various therapeutic classes in a variety of aqueous samples have been developed and method performance data are presented. The method involves the simultaneous extraction of the selected pharmaceuticals from the aqueous phase by solid phase extraction using a hyper cross linked, polystyrene-divinylbenzene polymer based sorbent. Analytes were eluted with methanol, derivatised with N-methyl-N-trimethylsilyltrifloroacetamide and analysed by gas chromatography – electron ionisation mass spectrometry (GC-EI-MS). Recoveries of 50 to 98% were established for waters spiked with the studied compounds at the low ng L^–1 level with the highest detection sensitivities being achieved in the selected ion monitoring (SIM) mode and the quantification limit of the procedure for sample sizes of 1000 ml was approximately 5 ng L^–1 for all matrices except sewage which was only tested to 20 ng L^–1. Analysis of domestic sewage from a large treatment works demonstrate the presence of all five compounds in both influents and effluents.     

Comparison of ultrasound-assisted extraction and direct immersion solid-phase microextraction methods for the analysis of monoterpenoids in wine

Ultrasound-assisted extraction (UAE) and direct immersion solid-phase microextraction (DI-SPME) were evaluated for the monoterpenic compounds determination in wine samples. The wine extracts obtained were analyzed by gas chromatography-mass spectrometry (GC-MS). The optimization of the variables affecting UAE and SPME methods was carried out in order to achieve the best extraction efficiency. Both UAE and SPME are quantitative (recoveries in the range 93-97% and 71.8-90.9%, respectively), precise (coefficients of variation below 5.5%), sensitive (limits of detection between 30-39 μg L⁻¹ and 11-25 μg L⁻¹, respectively) and linear over one order of magnitude. The application of both methods to red wine samples showed that UAE provided higher extraction of monoterpenic compounds than SPME. Although SPME remains an attractive alternative technique due to its speed, low sample volume requirements and solvent free character.     

Development and validation of a rapid multiresidue method for pesticide determination using gas chromatography-mass spectrometry: a realistic case in vineyard soils

A rapid and simultaneous method for residue identification and quantification for seven pesticides in agricultural soils has been developed to study a realistic situation in vineyard. The target compounds are two insecticides, two herbicides and three fungicides, from different chemical families. The procedure is based on a pressurized liquid extraction (PLE) with acetone, before a multiresidue GC-MS analysis. The recovery of PLE is between 53.8 ± 2.4 and 99.9 ± 4.4% according to pesticide. A limit of detection (LOD) between 1.4 and 4.6 μg kg⁻¹ of dry soil was obtained for five analytes. This procedure for testing soil contamination is sensitive and easy to perform.     

Comparative analysis of the volatile components in cut tobacco from different locations with gas chromatography-mass spectrometry (GC-MS) and combined chemometric methods

A combined approach of subwindow factor analysis and orthogonal projection resolution was used to analyze the volatile components of cut tobacco samples from different sources. After extracted with simultaneous distillation and extraction method, the volatile components in cut tobacco from five different locations were detected by GC-MS. Then, the qualitative and quantitative analysis of the volatile components of cut tobacco from Changde area was completed with the help of subwindow factor analysis resolving two-dimensional original data into pure mass spectra and chromatograms. One hundred and two volatile components among 138 separated peaks were identified and quantified, accounting for about 88.90% of the total content. Finally, orthogonal projection method was used to extract the common peaks from different locations. Among the identified components, there were 74 components coexisting in five studied samples although the relative content of each component showed difference to some extent. The results showed a fair consistency in their GC-MS fingerprints. It was the first time to apply orthogonal projection method to compare different cut tobacco samples, and it reduced the burden of qualitative analysis as well as the subjectivity. The obtained results proved the combined approach powerful for the analysis of complex cut tobacco samples. The developed method can be used to compare the sameness and differences of cut tobacco from different sources and for quality control of cigarette production and materials.     

A molecularly imprinted polymer as the sorptive phase immobilized in a rotating disk extraction device for the determination of diclofenac and mefenamic acid in wastewater

The microextraction of diclofenac and mefenamic acid from water samples was performed by using rotating disk sorptive extraction (RDSE) with molecularly imprinted polymer (MIP) as the sorptive phase. The MIP was synthesized from the monomer 1-vinylimidazol (VI) together with the cross-linker divinylbenzene (DVB) using diphenylamine as the template molecule. Scanning electron microscopy (SEM) analyses of the MIP revealed clusters of spherical particles having a narrow size distribution, with diameters of approximately 1 μm.     

Evaluation of alignment methods and data pretreatments on the determination of the most important peaks for the discrimination of coffee varieties Arabica and Robusta using gas chromatography-mass spectroscopy

Coffee samples were analyzed by GC/MS in order to determine the most important peaks for the discrimination of the varieties Arabica and Robusta. The resulting peak tables from chromatographic analysis were aligned and pretreated before being submitted to multivariate analysis. A rapid and easy-to-perform peak alignment procedure, which does not require advanced programming skills to use, was compared with the tedious manual alignment procedure. The influence of three types of data pretreatment, normalization, logarithmic and square root transformations and their combinations, on the variables selected as most important by the regression coefficients of partial least squares-discriminant analysis (PLS-DA), are shown. Test samples different from those used in the calibration and comparison with the substances already known as being responsible for Arabica and Robusta coffees discrimination were used to determine the best pretreatments for both datasets. The data pretreatment consisting of square root transformation followed by normalization (RN) was chosen as being the most appropriate. The results obtained showed that the much quicker automated aligned method could be used as a substitute for the manually aligned method, allowing all the peaks in the chromatogram to be used for multivariate analysis.