Low-pressure Gas Chromatography Research Articles

Ruggedness and other performance characteristics of low-pressure gas chromatography–mass spectrometry for the fast analysis of multiple pesticide residues in food crops☆

Low-pressure gas chromatography–mass spectrometry (LP-GC–MS) using a quadrupole MS instrument was further optimized and evaluated for the fast analysis of multiple pesticide residues in food crops. Performance of two different LP-GC–MS column configurations was compared in various experiments, including ruggedness tests with repeated injections of pesticides in matrix extracts. The tested column configurations employed the same 3 m × 0.15 mm i.d. restriction capillary at the inlet end, but different analytical columns attached to the vacuum: (A) a 10 m × 0.53 mm i.d., 1 μm film thickness RTX-5 Sil MS column; and (B) a 10 m × 0.25 mm i.d., 0.25 μm film thickness DB-5MS column. Under the optimized conditions (compromise between speed and sensitivity), the narrower analytical column with a thinner film provided slightly (<1.1-fold) faster analysis of <5.5 min separation times and somewhat greater separation efficiency. However, lower detection limits for most of the tested pesticides in real extracts were achieved using the mega-bore configuration, which also provided significantly greater ruggedness of the analysis (long-term repeatability of analyte peak intensities, shapes, and retention times). Additionally, the effect of the increasing injection volume (1–5 μl) on analyte signal-to-noise ratios was evaluated. For the majority of the tested analyte–matrix combinations, the increase in sensitivity caused by a larger injection did not translate in the same gain in analyte detectability. Considering the costs and benefits, the injection volume of 2–3 μl was optimal for detectability of the majority of 57 selected pesticides in apple, carrot, lettuce, and wheat extracts.

Ruggedness and other performance characteristics of low-pressure gas chromatography–mass spectrometry for the fast analysis of multiple pesticide residues in food crops

Low-pressure gas chromatography–mass spectrometry (LP-GC–MS) using a quadrupole MS instrument was further optimized and evaluated for the fast analysis of multiple pesticide residues in food crops. Performance of two different LP-GC–MS column configurations was compared in various experiments, including ruggedness tests with repeated injections of pesticides in matrix extracts. The tested column configurations employed the same 3 m × 0.15 mm i.d. restriction capillary at the inlet end, but different analytical columns attached to the vacuum: (A) a 10 m × 0.53 mm i.d., 1 μm film thickness RTX-5 Sil MS column; and (B) a 10 m × 0.25 mm i.d., 0.25 μm film thickness DB-5MS column. Under the optimized conditions (compromise between speed and sensitivity), the narrower analytical column with a thinner film provided slightly (<1.1-fold) faster analysis of <5.5 min separation times and somewhat greater separation efficiency. However, lower detection limits for most of the tested pesticides in real extracts were achieved using the mega-bore configuration, which also provided significantly greater ruggedness of the analysis (long-term repeatability of analyte peak intensities, shapes, and retention times). Additionally, the effect of the increasing injection volume (1–5 μl) on analyte signal-to-noise ratios was evaluated. For the majority of the tested analyte–matrix combinations, the increase in sensitivity caused by a larger injection did not translate in the same gain in analyte detectability. Considering the costs and benefits, the injection volume of 2–3 μl was optimal for detectability of the majority of 57 selected pesticides in apple, carrot, lettuce, and wheat extracts.

Single step determination of fragrances in Cucurbita flowers by coupling headspace solid-phase microextraction low-pressure gas chromatography–tandem mass spectrometry

Coupling headspace solid-phase microextraction (HS-SPME) and low-pressure gas chromatography–tandem mass spectrometry (LP–GC–MS–MS) has been used for determining 20 volatile compounds present in flowers. HS-SPME coupled with LP–GC–MS–MS acts in a synergic way allowing a fast extraction and analysis of the target compounds. The method has been optimised studying the influence of the adsorption temperature and adsorption time. The best results were obtained heating the SPME vials at 60 °C for 5 min using 65 μm poly(dimethylsiloxane–divinylbenzene) fibers. The validation of the method ensures the fitness for the purpose of the analytical method, achieving appropriate lower limits, recoveries and precision. The analytical method has been applied to the characterisation of zucchini flowers fragrances in air using passive sampling, in order to improve our knowledge on zucchini fragrances and to better pollination technique in future steps.

Fast chromatographic determination of polycyclic aromatic hydrocarbons in aerosol samples from sugar cane burning

Sugar cane burning in Brazil causes remarkable amounts of organic compounds to be emitted amongst which the polycyclic aromatic hydrocarbons (PAHs) represent serious health hazards. Therefore, 24-h aerosol samples (<10 μm aerodynamic diameter) were collected in Araraquara city (São Paulo state) during the harvest season using a Hi-Vol sampler. PAHs were recovered using an Accelerated Solvent Extractor and analyzed by low-pressure gas chromatography–ion trap mass spectrometry (LP-GC–IT-MS). The fully automated extraction process was performed in less than 25 min with a solvent consumption of approximately 20 ml. The use of a deactivated 0.6 m×0.10 mm i.d. restrictor coupled to a 10 m wide-bore analytical column allowed most of the 16 PAHs in EPA’s priority list to be identified and quantified in only 13 min. Concentrations of PAHs in Araraquara aerosols ranged between 0.5 and 8.6 ng m −3.

Application of low-pressure gas chromatography–ion-trap mass spectrometry to the analysis of the essential oil of Turnera diffusa (Ward.) Urb.

Turnera diffusa Willd. var. afrodisiaca (Ward) Urb. (syn. T. aphrodisiaca) belongs to the family of Turneraceae and is an aromatic plant growing wild in the subtropical regions of America and Africa. It is widely used in the traditional medicine as e.g. anti-cough, diuretic, and aphrodisiac agent. This work presents a 3 min chromatographic analysis using low-pressure (LP) gas chromatography (GC)–ion-trap (IT) mass spectrometry (MS). The combination of a deactivated 0.6 m×0.10 mm i.d., restrictor with a wide-bore CP-Wax 52 capillary column ( 10 m×0.53 mm i.d., 1 μm) reduces the analysis time by a factor of 3–7 in comparison to the use of a conventional narrow bore column. Chromatographic conditions have been optimized to achieve the fastest separation with the highest signal/noise ratio in MS detection. These results allow fast and reliable quality control of the essential oil to be achieved.

Rapid pesticide analysis, in post-harvest plants used as animal feed, by low-pressure gas chromatography-tandem mass spectrometry.

A wide range of pesticides used to control pests in vegetables have been determined in agricultural plant waste from beans, watermelons, and melons grown in greenhouses located in a predominantly agricultural area in Southeast Spain (Almería). Analysis of the pesticides was carried out by low-pressure gas chromatography (LP-GC) with mass spectrometry in tandem (MS-MS) mode, after extraction of the lyophilized samples with dichloromethane. The influence of the sample matrix on the analysis was avoided by use of matrix-matched standards. Linearity, detection limit ( LOD), quantitation limit ( LOQ), recovery, and precision for each pesticide were calculated. The most frequently encountered pesticides were endosulfan (>73% of the analyzed samples) and buprofezin (>55% of the samples), followed by cypermethrin, pirimifos-methyl, bifentrin, and chlorpyrifos (>30% of the samples). The pesticide found at the highest concentration level was endosulfan (223.33 mg kg(-1)) in a watermelon sample.

Reduction of analysis time in gas chromatography: Application of low-pressure gas chromatography–tandem mass spectrometry to the determination of pesticide residues in vegetables

An alternative to conventional capillary gas chromatography (GC) is evaluated as a new approach to determine pesticide residues in vegetables. Low-pressure gas chromatography–tandem mass spectrometry (LP-GC–MS–MS) is proposed after a fast and simple extraction of the vegetable samples with dichloromethane and without clean up. The use of the above-mentioned GC technique reduced the total time required to determine 72 pesticides to less than half the present time (31 min), increasing the capability of a monitoring routine laboratory. The use of guard column and plug of carbofrit into the glass liner in combination with LP-GC was evaluated. The method was validated with limits of quantitation low enough to determine the pesticide residues at concentrations below the maximum residue levels stated by legislation. In order to assess its applicability to the analysis of real samples, 25 vegetable samples previously determined using conventional-capillary GC–MS–MS were analysed by LP-GC–MS–MS. The results obtained with the compared techniques showed differences lower than 0.01 mg kg −1.

Selective Extraction and Determination of Multiclass Pesticide Residues in Post-Harvest French Beans by Low-Pressure Gas Chromatography/Tandem Mass Spectrometry

A selective and reliable extraction procedure was developed and validated to determine multiclass pesticide residues in lyophilized agricultural plants by low-pressure gas chromatography coupled with tandem mass spectrometry. The method is based on a rapid and simple extraction of the lyophilized sample with dichloromethane. The results were compared with those obtained by using fresh and naturally dried samples. Slightly better recoveries and precision values were obtained for the lyophilized samples. The application of the proposed methodology was tested by analyzing French bean plants from an agricultural area of Almería (Spain). The availability of this methodology, which is capable of detecting a high number of analytes in a single analysis, has priority in analyses for a large number of pesticides used on individual commodities.

Trace analysis of benzene, toluene, ethylbenzene and xylene isomers in environmental samples by low-pressure gas chromatography–ion trap mass spectrometry

A rapid determination of benzene, toluene, ethylbenzene and the three xylene isomers (BTEX), including a nearly baseline separation of the xylene isomers in environmental samples within 1 min has been carried out using low-pressure gas chromatography–ion trap mass spectrometry (LP-GC–IT-MS). In order to evaluate the different parameters which may influence the performance of LP-GC–IT-MS, different column and mass spectral parameters were varied. Comparing LP-GC–IT-MS with the conventional equivalent, we obtained excellent detection limits as well as a good RSD of 8–13% in addition to a much shorter analysis time. In order to evaluate LP-GC–IT-MS for use in environmental samples, we determined BTEX in air.

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×0.53 mm I.D., 1 μm film thickness coupled with a 3 m×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.

Chemical kinetic study of dimethylether oxidation in a jet stirred reactor from 1 to 10 ATM: Experiments and kinetic modeling

The oxidation of dimethyl ether (DME) has been studied in a jet-stirred reactor (JSR). The experiments cover a wide range of conditions: 1–10 atm, 0.2≤≤2.0, 800–1300 K. Concentration profiles of reactants, internediates, and products of the oxidation of DME were measured in a fused silica JSR by low-pressure, sonic-probe sampling and off-line gas chromatography analyses. These results represent the first detailed kinetic study of DME oxidation in a reactor. They demonstrate that the oxidation of DME does not yield higher molecular weight compounds. A numerical model consisting of a detailed kinetic-reaction mechanism with 286 reactions (most of them reversible) among 43 species describes DME oxidation in a JSR. A generally good agreement between the data and the model was observed. The kinetic modeling is used to interpret the data.

Low-Pressure Gas Chromatography with Split Injection and Photoionization Detection

Low-Pressure Gas Chromatography with Split Injection and Photoionization Detection

Characterization of high boiling Fischer-Tropsch liquids by liquid and gas chromatography

Hydrocarbons and oxygenates present in Fischer-Tropsch liquids boiling above 170/sup 0/C (C10+) were characterized by preparative low-pressure liquid chromatography and gas chromatography. Olefins and paraffins were resolved by argentation liquid chromatography. The major compound classes detected were paraffins, olefins, alcohols, ketones, esters, and carboxylic acids. Carbon number distribution plots of olefins and oxygenates were very similar, both classes being detected to approximately C20 to C25. Paraffins were detected to C30 to C40+.

Low pressure gas chromatography

Low pressure gas chromatography