Estimation of Olefin Dimerisation Products by GC/GC–MS and IR Techniques

A GC and IR based protocol was developed for monitoring the isobutene dimerisation process wherein the complete characterisation of the products was carried out by GC coupled with mass spectrometry. In the dimerisation process, LPG from FCC process comprising a mixture of saturated and unsaturated C4 hydrocarbons is subjected to a dimerisation process using a catalyst to produce C8 hydrocarbons. The reaction is carried out keeping in view the demand for high-octane blending components in gasoline. The isooctene generated in the process (mainly from the dimerisation of isobutene) is converted into isooctane having the RON and MON value 100. The monitoring process requires the use of two different column chemistries, viz., a 100 m CPSIL PONA CB non-polar column for C8 and its isomers and an Alumina PLOT column for C4 hydrocarbons. A 100 m non-polar column does not separate the C4 mixture since the column is meant for gasoline range products containing C5 and above hydrocarbons. Therefore, a need was felt for an improvised method which can handle both the analyses simultaneously. A cryogenic oven program starting from 0 °C was developed for separating the isomers of C4 hydrocarbons and C8 hydrocarbons on a single column during the single run by Detailed Hydrocarbon Analyzer. The data obtained using the cryo programme was validated with data obtained using Alumina PLOT column on C4 mixture since the Alumina PLOT column is the widely accepted column chemistry for separating the C4 hydrocarbons. An IR method for the estimation of the total olefin content was developed using 2,2,4-trimethyl pentene-1 as the reference standard. The total olefins generated during the process were identified by GC–MS, quantified by DHA-FID and validated by infrared spectroscopy. A good correlation was found between GC and IR spectral results (correlation coefficient R ²  = 0.99).     

GC–MS Determination of Sucralose in Splenda

Sucralose (1,6-dichloro-1,6-dideoxy-β-d-fructofuranosyl-4-chloro-4-deoxy-α-d-galactopyranoside) is a high-intensity non-nutritive sweetener derived from sucrose. Determination of sucralose in food is important to ensure consistent product quality. The authors have developed a new method for determination of sucralose. The sucralose was converted into its trimethylsilyl (TMS) ether and qualitative and quantitative analysis were achieved by GC–MS and GC–FID, respectively, using myo-inositol ester as the internal standard. A good linear relationship between response and amount of sucralose TMS ether was obtained in the range 0.005–0.06 mg mL^?1 (r = 0.9994). The detection limit was 0.25 ng.     

Characteristics Identification of Neutral Constituents in Cigarette Particulate Matter by GC × GC -TOF MS

建立了全二维气相色谱-飞行时间质谱( GC×GC - TOF MS)分析卷烟主流烟气中中性化学成分的方法.以较长的弱极性柱HP-5 MS(50 m×0.2 mm i.d.×0.33 μm)作为第一维柱,较短的薄液膜中等极性柱DB-17MS(1.7 m×0.1 mm i.d.×0.1 μm)作为第二维柱,对优质烟叶单料卷烟烟气的中性成分进行定性分析,经过人工纠错等分析初步鉴定出匹配度大于700的1 464种成分,重点讨论了中性香味羰基化合物全二维点阵的谱图特征,为烟气和复杂体系的深入研究提供了方法学基础.     

GC�CMS and GC�CNPD Determination of Formaldehyde Dimethylhydrazone in Water Using SPME

Formaldehyde dimethylhydrazone (FADMH) is one of the important transformation products of residual rocket fuel 1,1-dimethylhydrazine (1,1-DMH). Thus, recent studies show that FADMH toxicity is comparable to that of undecomposed 1,1-DMH. In this study, a new method for quantification of FADMH in water based on solid phase microextraction (SPME) in combination with gas chromatography (GC) with mass spectrometric (MS) and nitrogen-phosphorus detection (NPD) is presented. Effects of SPME fiber coating type, extraction and desorption temperatures, extraction time, and pH on analyte recovery were studied. The optimized method used 65 micron polydimethylsiloxane/divinylbenzene fiber coating for 1?min headspace extractions at 30?°C. Preferred pH and desorption temperature from the SPME fiber are >8.5 and 200?°C, respectively. Detection limits were estimated to be 1.5 and 0.5?μg?L(-1) for MS and NPD, respectively. The method was applied to laboratory-scale experiments to quantify FADMH. Results indicate applicability for in situ sampling and analysis and possible first-time detection of free FADMH in water.     

Comprehensive multidimensional separation methods by hyphenation of single-photon ionization time-of-flight mass spectrometry (SPI-TOF-MS) with GC and GC×GC

One- and comprehensive two-dimensional gas chromatography were hyphenated with soft photoionization mass spectrometry. The characteristics of these two- and three-dimensional comprehensive separation techniques are discussed in detail. Using the innovative electron beam pumped excimer light source (EBEL) for single-photon ionization (SPI), organic molecules with ionization energies (E _i ) of below 9.8 eV can be detected by a time-of-flight mass spectrometer (TOF-MS). SPI with 126 nm vacuum ultraviolet (VUV) photons enables the universal and soft ionization of organic molecules. SPI-TOF-MS hyphenated to one-dimensional gas chromatography results in a comprehensive two-dimensional separation method (GC×MS). To demonstrate this, diesel fuel was analyzed, and the resulting GC×MS chromatograms are discussed in depth. A three-dimensional separation method was also realized by combining comprehensive two-dimensional gas chromatography (GC×GC) with SPI-MS. In the resulting separation space, constituents originating from mineral oil diesel blended with biodiesel were dispersed along the two GC separation axes, while the molecular mass axis served as a third separation dimension.     

The use of GC×GC/TOF MS with multivariate analysis for the characterization of foodborne pathogen bacteria profiles

The cellular fatty acid profiles of eight strains of Bacillus, Staphylococcus, and Enterobacteriacae (Escherichia coli and Salmonella) were analyzed by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry. A novel template method was developed to standardize the raw two-dimensional gas chromatography retention data through the use of a chemical indexing mixture. Analyte retention coordinates were normalized in the primary dimension with respect to a series of n-alkanes (Kovats index) and in the secondary dimension with respect to a series of aromatic hydrocarbons (Lee index). Fatty acid profiles extracted from the templates were compared by multidimensional scaling and principal component analysis. Differences in the profiles of Gram-positive and Gram-negative bacteria were observed, and a series of heterogeneous mixtures comprising different fractions (containing one Gram-positive and one Gram-negative bacteria strain) were also distinguished from their homogeneous constituents.     

Characterisation of VOC composition of Slovak monofloral honeys by GC��GC-TOF-MS

Solid phase microextraction (SPME) followed by comprehensive two-dimensional gas chromatography coupled to a time-of-flight mass spectrometer (GC×GC-TOF-MS) was used to characterise volatile organic compounds in honeys of different botanical origins. Rape, sunflower, acacia, lime, raspberry, and phacelia honeys from Slovakia were studied in detail. Up to 900 compounds were detected at the given S/N ratio of 200. The poorest VOC profiles were found for acacia and rape honeys while lime honey showed the richest VOC composition. Approximately 100 compounds were present in all honeys studied, independently of their botanical origin. They belong to various chemical classes (hydrocarbons, alcohols, aldehydes and ketones, terpenes, benzene derivatives, and compounds containing heteroatoms). The compounds found in only one type of honey were also successfully identified.     

Simultaneous Analysis of Lipid-Soluble Constituents of Erxian Decoction by GC–MS

Erxian Decoction (EXD), a traditional Chinese medicine formula mainly composed of six Chinese herbs, was originally developed for menopausal syndromes and had been practiced since the 1950s in China. Previous studies only focused on the water-soluble compounds involved in EXD by LC or TLC. This study analyzed the whole profile of the volatile constituents contained in EXD to supplement its quality evaluation method. Several EXD samples were extracted with chloroform and ethyl acetate, respectively, to get the lipid-soluble chloroform and ethyl acetate fractions and compared their gas chromatographic profiles by GC–MS. The EXD samples were hydrolyzed with hydrochloric acid in a water-bath at 100 °C, neutralized with 40% NaOH, and finally extracted with ethyl acetate and chloroform for the quantification of the total sarsasapogenins contained in EXD. A total of 56 compounds belonging to a variety of natural product categories such as aromatic phenols, terpenes, fatty acids, ketones, esters, and aldehydes, etc. were identified from the chloroform and ethyl acetate extracts by using the online EI–MS characterization. The GC–MS method showed a linear response for sarsasapogenin quantification with r = 0.994. The intra-day and inter-day variations of precision and accuracy of the assay were less than 5%. This developed GC–MS method could thus be successfully applied for the identification of lipid-soluble constituents derived from EXD, and also for the accurate quantification of the total sarsasapogenins contained in the acid hydrolyzed EXD samples.     

Fast GC–MS Pesticide Multiresidue Analysis of Apples

A fast gas chromatographic–mass spectrometric (GC–MS) method is proposed for pesticide multiresidue analysis of apples. The QuEChERS method was used for sample preparation. GC–MS analysis was performed with a PTV, an autoinjector, and a quadrupole benchtop MS detector. Electron-impact ionization (70 eV) was used with two modes of selected ion monitoring. Compounds were separated under temperature-programmed conditions on a narrow-bore diphenyldimethylsiloxane column. In one chromatographic run 61 pesticides of different chemical classes, and triphenyl phosphate as internal standard, were determined in 11 min. Calibration was performed with matrix-matched standard solutions and response to the pesticides was a linear function of concentration in the range 1–500 ng mL⁻¹ (equivalent to 1–500 μg kg⁻¹ in real samples). High values of the determination coefficients (R ²; 0.9900–1.0000) were obtained for most of the pesticides. Limits of detection and quantification were determined. When the method was used for analysis of pesticide residues in real samples, five pesticides were detected at concentrations in the range 1.00–21.47 μg kg⁻¹. Repeatability of measurements, expressed as relative standard deviations of absolute peak areas, normalized relative to TPP, and of the concentrations determined, met the EU criterion of RSD ≤ 20%. Use of the internal standard moderately improved quantitative results.

     

Determination of elaidic and vaccenic acids in foods using GC×GC-FID and GC×GC-TOFMS

Trans fatty acids (TFAs) are present in meat and dairy products as m ruminant animals and in vegetable fats due to partial hydrogenation. This study aimed to discriminate between natural (N-TFA) and hydrogenated trans fatty (H-TFA) acids by GC × GC-flame ionization detection (GC × GC-FID) and comprehensive GC × GC-time-of-flight mass spectrometry (GC × GC-TOFMS). The separation of two kinds of trans fats, vaccenic acid (18:1 trans-11) and elaidic acid (18:1 trans-9), was performed using GC × GC-FID and GC × GC-TOFMS. A 100 m × 0.25 mm I.D. × 0.2 μm (film thickness) SP-2560 (bis-cyanopropyl polysiloxane) fused capillary column (first separation dimension, 1D) was coupled to a 1.5 m × 0.18 mm I.D. × 0.18 μm (film thickness) RTX-5 (5% diphenyl/95% dimethyl polysiloxane) fused capillary column (second separation dimension, 2D). The RSD of the intra-day repeatability by both GC × GC-FID and GC × GC-TOFMS for elaidic and vaccenic acids was ≤9.56% and ≤9.97%, and the RSD of the inter-day repeatability was ≤8.49 and ≤9.06%, respectively. It was found that the V/E value (vaccenic acid to elaidic acid ratio) could be used to distinguish H-TFA from N-TFA and to evaluate the quality of the fatty foods.     

Development of an analytical method for the determination of the residues of four pyrethroids in meat by GC–ECD and confirmation by GC–MS

The development of an analytical method for the determination of four selected pyrethroid insecticides at residue level in beef meat is presented. Acetone and petroleum ether at 40-60 degrees C were chosen as extraction solvents. A two-step clean-up was performed using an Extrelut NT3-C(18) system followed by a Florisil column, with disposable, ready-to-use cartridges. Instrumental analysis was carried out on a gas chromatograph equipped with an electron capture detector (GC-ECD), using matrix-matched and internal standard calibration techniques. Confirmatory analysis by GC-MS was performed. Recoveries at the EU Maximum Residue Limit (MRL), 0.5 x MRL and 1.5 x MRL levels and the repeatabilities were widely satisfactory. The main advantage of the method was the reduction of analysis time as compared with previously published works. The applicability of the method to different matrices and pesticide classes will be investigated.     

Determination of Milnacipran in Human Plasma Using GC–MS

A new, simple, and fully validated gas chromatography–mass spectrometry (GC–MS) method was presented for quantitative analysis of milnacipran (MNP) in human plasma. MNP was efficiently derivatized with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) before analysis. The role of catalyst, temperature, time, solvent on the trimethylsilylation reaction were evaluated. The proposed method was fully validated by assessment of the following parameters: limits of detection and quantitation, precision, accuracy, linearity, specificity, stability, extraction recovery and robustness/ruggedness. The limit of quantitation (LOQ) was 30 ng mL^?1. The calibration curve was linear (r ² > 0.9988) in the range 30–500 ng mL^?1. The method was found specific, precise, accurate, selective and reliable according to validation data. This developed method was successfully applied to determine the steady state concentration of MNP in patients.     

A Good GC Stationary Phase for Separation of Xylene Isomers

TheseparationofxyleneisomersusingGCisamuchdifficulttaskforalongtime,ontheotherhandtheyareveryimpoFtantindustrialmaterials,sofindingagoodstationaryphasehasbeenaninterestingwork.Anexcellentseparationofxyleneisomerswasobtainedbyusing2,6-di-O-pentyl-3-O...     

Derivatization Method for Determination of Nitrosamines by GC�CMS

Gas chromatography/low-resolution mass spectrometry with electron impact source was applied to detect eight nitrosamines (NAs). NAs were first denitrosated by a mixed solution of hydrobromic and acetic acids, followed by sulfonylation with p-toluenesulfonyl chloride. Variables affecting the denitrosation and sulfonylation, such as temperature, time, pH and reagent concentration, were optimized. Comparison of the determination of NAs with and without derivatization was performed. Results showed that better chromatographic behavior and larger mass response were obtained after derivatization, and instrumental detection limits ranged from 0.016 to 0.053 ng, a nearly 20-fold decrease of those without derivatization. The proposed method provided an alternative to performing accurate qualitative and quantitative analysis of NAs with expensive high-resolution mass spectrometry or thermal energy analyzer.     

Determination of flurbiprofen in pharmaceutical preparations by GC–MS

This article describes a gas chromatography–mass spectrometry (GC–MS) method for the determination of flurbiprofen in pharmaceutical preparations. The method is based on the derivatization of flurbiprofen with N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). For GC–MS, electron ionization mode (EI = 70 eV) and selected ion monitoring (SIM) mode were used for quantitative analysis (m/z 180 for flurbiprofen). Calibration curve was linear between the concentration range of 0.25–5.0 μg/mL. Intra- and inter-day precision values for flurbiprofen were less than 3.64, and accuracy (relative error) was better than 2.67%. The mean recovery of flurbiprofen was 99.4% for pharmaceutical preparations. The limits of detection and quantification of flurbiprofen were 0.05 and 0.15 μg/mL, respectively. No interference was found from tablet excipients at the selected assay conditions. Also, the method was applied for the quality control of five commercial flurbiprofen dosage forms to quantify the drug and to check the formulation content uniformity.     

Use of Large Retention Index Database for Filtering of GC–MS False Positive Identifications of Compounds

The use of the large retention index database for identification and filtering of false positive hits in GC–MS analysis of the ylang-ylang essential oil is illustrated. Differences between experimental retention indices and database values of retention indices of candidate compounds provide additional constraints on the list of candidates for a target compound. Over 100 components of ylang-ylang essential oil (total grade) were identified. The main components, with concentrations more than 4?%, are β-caryophyllene, germacrene D, benzyl benzoate, linalool, geranyl acetate, α-(E,E)-farnesene and isobornyl acetate.     

DETECTION AND QUANTITATION OF TRACE ETHYL CARBAMATE IN ALCOLLOLIC BEVERAGES BY GC/GC AND GC/GC/MS

Analytical difficulties encountered in the determination of ethyl carbamate, aknown cancinogen, in a wide variety of wines and spirits have been overcome by spe-cific, sensitive GC/GC and CC/CC/MS methods with a relatively shorter extractionprocedure. The lowest detection limits were estimated to be 0. 1 and 0. 01μg/L forGC/GC and GC/GC/MS respectively. The RSD of the GC/GC method was 2. 5%.