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1.
J Chromatogr A ; 1614: 460737, 2020 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-31831145

RESUMO

This paper reports the development of a stationary phase thickness gradient gas chromatography (GC) column that enables analyte peak focusing and improves separation resolution. Theoretical analysis and simulation demonstrate focusing via a positive thickness gradient, i.e., the stationary phase thickness increases along the column. This effect was experimentally verified by coating a 5 m long capillary column with a film thickness varying from 34 nm at the column inlet to 241 nm at the column outlet. The column was analyzed in forward (thin to thick) and backward (thick to thin) modes and compared to a uniform thickness column with a thickness of 131 nm, using alkanes ranging from C5 to C16 and aromatics. Comparison of resolutions between forward mode and the uniform thickness column demonstrated an overall focusing rate (i.e., improvement in peak capacity) of 11.7% on alkanes and 28.2% on aromatics. The focusing effect was also demonstrated for isothermal room temperature separation of highly volatile compounds and temperature programmed separation with different ramping rates. In all cases, peak capacities from forward mode separations are higher than those from other modes, indicating the ability of a positive thickness gradient to focus analyte peaks. This thickness gradient technique can therefore be broadly applied to various stationary phases and column types as a general method for improving GC separation performance.


Assuntos
Técnicas de Química Analítica/métodos , Cromatografia Gasosa/instrumentação , Alcanos/química , Temperatura
2.
J Chromatogr A ; 1609: 460460, 2020 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-31445802

RESUMO

Fast gas chromatography that leverages the high chromatographic efficiency of narrow bore capillary column technology and temperature programming was successfully integrated with a third-generation low void-volume, 3D-printed two-stage microreactor. Effective management of extra-column effect and the capability to perform post-column backflushing were achieved with the incorporation of a recently commercialized, electronically controlled pneumatic switching device and a deactivated metal three-way microdevice. With this configuration, narrow bore capillary columns having internal diameters between 0.10 and 0.15 mm can be employed to produce chromatographic peaks in the domain of fast gas chromatography, with peak widths at half-height ranging from 0.42 s to 0.92 s for probe compounds having k over a range from 1.7 for toluene to 60 with the last analyte (nC44) eluted in less than 12 min. The carbon independent response capability of the 3D-printed microreactor affords unique and advantaged differentiators, for instance, conducting measurement of the target analytes using one single carbon-containing compound for calibration with an acceptable accuracy of ±10%, achieving a higher degree of accuracy by eliminating the need for multi-level and multi-compound calibration, and improving sensitivity for compounds that are not efficiently ionized by flame ionization detection. Using this platform, repeatability of retention times for 14 probe compounds was less than 0.1% RSD (n = 10), and less than 1.0% RSD (n = 10) for area counts. The utility of the analytical approach was illustrated with relevant, challenging applications.


Assuntos
Cromatografia Gasosa/instrumentação , Carbono/análise , Cromatografia Gasosa/métodos , Ionização de Chama/instrumentação , Impressão Tridimensional , Temperatura
3.
J Chromatogr A ; 1609: 460486, 2020 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-31506165

RESUMO

Most adsorbent materials used for preconcentrating and thermally desorbing volatile and semi-volatile organic compounds (S/VOCs) in portable or "micro" gas chromatographic (GC/µGC) instruments preferentially capture non-polar or moderately polar compounds relative to more polar compounds. Here, we explore the use of a known trigonal-tripyramidal room-temperature ionic liquid (RTIL) as a surface modifier for the graphitized carbons, Carbopack B (C-B) and Carbopack X (C-X), with the goal of enhancing their capacity and selectivity for polar S/VOCs. Breakthrough tests were performed by challenging tubes packed with ∼2.5 mg of C-B or RTIL-coated C-B (RTIL/C-B) with 13 individual S/VOCs, including several organophosphorus compounds and reference alkyl and aromatic hydrocarbons of comparable vapor pressures, at concentrations ranging from 14 to 130 mg/m3. The 10% breakthrough volume, Vb10, was used as the measure of capacity. For the RTIL/C-B, the Vb10 values of the five organophosphorus vapors tested were consistently ∼2.5 times larger than those for the untreated C-B, and Vb10 values of the four non-polar reference vapors were 11-26 times smaller for the RTIL/C-B than for the untreated C-B. For compounds of similar vapor pressure the capacity ratios for polar vs. non-polar compounds with the RTIL/C-B ranged from 1.8 to 34. Similar results were obtained with C-X and RTIL/C-X on a smaller set of compounds. Tests at 70% relative humidity or with a binary mixture of a polar and non-polar compound had no effect on the capacity of the RTIL/C-B, and there were no changes in Vb10 values after several months of testing that included cycling from 25 to 250 °C. Capacity was strongly correlated with vapor pressure. Attempts to reconcile the selectivity using models based on linear-solvation-energy relationships were only partially successful. Nonetheless, these results indicate that RTIL coating of carbon adsorbents affords a simple, reliable means of rendering them selective for polar S/VOCs.


Assuntos
Carbono/química , Cromatografia Gasosa/métodos , Líquidos Iônicos/química , Compostos Orgânicos Voláteis/química , Cromatografia Gasosa/instrumentação , Gases/química , Grafite/química , Hidrocarbonetos Aromáticos/química , Temperatura
4.
J Chromatogr A ; 1609: 460488, 2020 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-31519408

RESUMO

We report the discovery, preliminary investigation, and demonstration of a novel form of differential flow modulation for comprehensive two-dimensional (2D) gas chromatography (GC×GC). Commercially available components are used to apply a flow of carrier gas with a suitable applied auxiliary gas pressure (Paux) to a T-junction joining the first (1D) and second (2D) dimension columns. The 1D eluate is confined at the T-junction, and introduced for 2D separation with a cyclic rhythm, dependent upon the relationship of the modulation period (PM) to the pulse width (pw), where pw is defined as the time interval when the auxiliary gas flow at the T-junction is off. We refer to this flow modulation technique as "dynamic pressure gradient modulation" (DPGM) since a pressure gradient oscillates with the PM along the 1D and 2D column ensemble providing temporary stop-flow conditions and fast 2D flow rates, resulting in 100% duty cycle and full modulation. A 90-component test mixture was used to evaluate the technique with a pw of 60 ms and a PM of 750 ms. The resulting peaks were narrow, with 2Wb ranging from about 20-180 ms. With an average 1Wb of 3 s and a 2nc of 10, a 2D peak capacity, nc,2D, for the 25 min separation was 5000. The detector response enhancement factor (DREF) is reported, defined as the peak height of the highest modulated 2D peak divided by the unmodulated 1D peak height (DREF = 2h/1h). The DREF ranged from about 7-87, depending on the 1Wb and 2Wb for a given analyte. A diesel sample was analyzed to demonstrate performance with a complex sample. Based upon the average 1Wb of 5 s and an average 2Wb of 168 ms, a nc,2D of 8640 was obtained for the 60 min diesel separation. Finally, the modulation principle was investigated as a function of PM, pw, and the volumetric flow rates, 1F and 2F. The measured 2Wb correlate well with the theoretical 2D injected width, given by 2Winj = (1F/2F) ·PM. However, the relevant 1F appears to be dictated by the 1D flow rate when no pressure is applied (during the pw interval), instead of 1F being the average flow rate on 1D (defined by the 1D dead time). The findings provide strong evidence for a differential flow modulation mechanism.


Assuntos
Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Pressão
5.
Molecules ; 24(23)2019 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-31816831

RESUMO

The dynamic sorption concentration of explosive vapours on concentrators made of a metal mesh, and the transportation of explosive vapours through the extended metal channels are considered. The efficiency of the concentration and transportation is determined by the breakthrough of the substance's molecules through the channels. The research methods we used were breakthrough calculation theory and experiment. When calculating the breakthrough, a mesh was presented as a set of parallel identical channels. Wire mesh and extended channels were made of stainless steel. The breakthrough is determined through the specific frequency of the collisions between the molecules and the channel's surface. This is presented as a function of the ratio of the substance diffusion flow to the channel's surface to the airflow through the channel. The conditions for high-speed concentration, complete capture of explosive vapours, and low vapour losses during their transportation through the extended channels were determined theoretically and experimentally. For a concentrator made of a mesh, the condition of a high concentration rate at a high breakthrough (up to 80%) was determined. The described sorption concentration is used in portable gas chromatographic detectors of explosive vapours of the EKHO series.


Assuntos
Cromatografia Gasosa/instrumentação , Substâncias Explosivas/análise , Monitoramento Ambiental/instrumentação , Gases , Cinética
6.
J Food Sci ; 84(9): 2402-2411, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31429486

RESUMO

Diuron is a urea herbicide that is frequently detected in surface water, groundwater, and marine waters. However, there are few methods or guidelines reported on ensuring the quality of sugarcane and soil. In this study, a method was developed for detecting diuron to ensure the quality and safety of food and sugar. Mass spectrometry was used to identify 3,4-dichloroaniline as a marker for the thermal decomposition of diuron, and thus, as a representative component for quantitative diuron analysis. This approach can be used to rapidly detect trace amounts of diuron. In addition, ultrasound-assisted extraction (UAE) and carbon nanotube column purification were used in conjunction with gas chromatography-electron capture detection to detect diuron. The method was then evaluated for its accuracy, detection limit, and viability. The effects of extraction solvent, ultrasound time, and ultrasound power on the extraction efficiency of the analyte from sugarcane and soil were also investigated. The efficiency and optimum conditions of UAE were examined through single-factor experiments and Box-Behnken design (BBD). The optimal extraction conditions were identified as follows: acetonitrile as the extraction solvent, extraction temperature of 27 °C, extraction time of 3.4 min, and ultrasound power of 70 W. Under these conditions, high linearity was achieved for diuron concentrations of 0.01 to 5.0 mg/L, and the purification correlation coefficient was consistently greater than 0.998. Hence, gas chromatography, combined with UAE and BBD, offers superior efficiency extraction, which is sufficiently accurate and precise for pesticide residue analysis. PRACTICAL APPLICATION: We developed an accurate and cost-effective method for detecting diuron (a commonly used herbicide) in soil and sugar samples. We performed experiments to determine the optimum detection conditions for our method. This method can be used for online monitoring of sugar manufacturing processes to ensure food safety and quality.


Assuntos
Cromatografia Gasosa/métodos , Diurona/análise , Herbicidas/química , Saccharum/química , Poluentes do Solo/química , Extração em Fase Sólida/métodos , Ultrassom/métodos , Cromatografia Gasosa/instrumentação , Diurona/isolamento & purificação , Elétrons , Contaminação de Alimentos/análise , Herbicidas/isolamento & purificação , Limite de Detecção , Espectrometria de Massas , Nanotubos de Carbono/química , Resíduos de Praguicidas/química , Resíduos de Praguicidas/isolamento & purificação , Poluentes do Solo/isolamento & purificação , Extração em Fase Sólida/instrumentação
7.
Anal Bioanal Chem ; 411(24): 6435-6447, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31367803

RESUMO

Acute respiratory distress syndrome (ARDS) is the most severe form of acute lung injury, responsible for high mortality and long-term morbidity. As a dynamic syndrome with multiple etiologies, its timely diagnosis is difficult as is tracking the course of the syndrome. Therefore, there is a significant need for early, rapid detection and diagnosis as well as clinical trajectory monitoring of ARDS. Here, we report our work on using human breath to differentiate ARDS and non-ARDS causes of respiratory failure. A fully automated portable 2-dimensional gas chromatography device with high peak capacity (> 200 at the resolution of 1), high sensitivity (sub-ppb), and rapid analysis capability (~ 30 min) was designed and made in-house for on-site analysis of patients' breath. A total of 85 breath samples from 48 ARDS patients and controls were collected. Ninety-seven elution peaks were separated and detected in 13 min. An algorithm based on machine learning, principal component analysis (PCA), and linear discriminant analysis (LDA) was developed. As compared to the adjudications done by physicians based on the Berlin criteria, our device and algorithm achieved an overall accuracy of 87.1% with 94.1% positive predictive value and 82.4% negative predictive value. The high overall accuracy and high positive predicative value suggest that the breath analysis method can accurately diagnose ARDS. The ability to continuously and non-invasively monitor exhaled breath for early diagnosis, disease trajectory tracking, and outcome prediction monitoring of ARDS may have a significant impact on changing practice and improving patient outcomes. Graphical abstract.


Assuntos
Testes Respiratórios/instrumentação , Cromatografia Gasosa/instrumentação , Síndrome do Desconforto Respiratório do Adulto/diagnóstico , Gasometria , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Monitorização Fisiológica , Prognóstico
8.
J Chromatogr A ; 1606: 460384, 2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31371199

RESUMO

With detection limits in the low ppbv-range, electron capture detectors (ECD) are the most sensitive GC-detectors available for electron affine compounds, such as pesticides or chlorofluorocarbons. The working principle is based on the generation of free electrons at atmospheric pressure, which are usually emitted from a radioactive Ni-63 source. However, the use of radioactive materials leads to regulatory restrictions regarding purchase, operation and disposal. Recently, we introduced a novel ECD based on a non-radioactive electron source, achieving comparable detection limits, e.g. 1 ppbv (6 ng/l) for 1,1,2-trichloroethane. However, the linear range was still below that of radioactive ECDs. In addition, the detector volume was too large to be used as a GC detector. We now present an improved version of this non-radioactive ECD with significantly increased linear range of 6.5∙103 for 1,1,2-trichloroethane by implementing pulsed operation using a newly developed, autonomous control electronics. In addition, the detector volume is reduced to 100 µl, leading to faster response times, less memory effects and thus less peak broadening. The improved ECD with non-radioactive electron source reaches similar analytical performance compared to commercially available radioactive ECDs and thus can be used as a possible replacement of radioactive ECDs.


Assuntos
Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Elétrons , Radioatividade , Pressão Atmosférica , Limite de Detecção , Praguicidas/análise
9.
J Chromatogr A ; 1608: 460420, 2019 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-31405571

RESUMO

Chiral crystalline sponges (CCSs) are a recent class of chiral porous metal complexes potential in chiral recognition. Here we report the fabrication of polysiloxane OV-1701 incorporated CCS-3S (PSO/CCS-3S) coated capillary column as a novel stationary phase for gas chromatographic separation of diverse racemates. CCS-3S with the chiral ligand of (S)-mandelic was selected as the model CCS. With the aid of polysiloxane OV-1701, PSO/CCS-3S coated capillary column gave improved resolution, broader enantiomers separation scope and much larger McReynolds constants than CCS-3S coated capillary column. Many racemates that cannot be separated on CCS-3S coated capillary column were well resolved on PSO/CCS-3S coated capillary column. The PSO/CCS-3S coated capillary column also gave wide linear range, low limit of detection, good repeatability and reproducibility, and fine inertness and anti-column bleeding properties for the separation of enantiomers. In addition, the PSO/CCS-3S coated capillary column presented better resolution for the studied racemates than commercial ß-cyclodextrin based Cyclosil B (30 m long ×0.32 mm i.d. × 0.25 µm film thickness), ß-DEX 225 (30 m long ×0.25 mm i.d. × 0.25 µm film thickness) and amino acid based Chirasil L-Val (25 m long ×0.25 mm i.d. × 0.12 µm film thickness) capillary columns. These results indicate the great potential of PSO/CCS-3S coated capillary column in separation of enantiomers.


Assuntos
Cromatografia Gasosa/instrumentação , Siloxanas/química , Cromatografia Gasosa/métodos , Compostos Orgânicos/química , Compostos Orgânicos/isolamento & purificação , Reprodutibilidade dos Testes , Estereoisomerismo , beta-Ciclodextrinas/química
10.
Artigo em Inglês | MEDLINE | ID: mdl-31229913

RESUMO

Two simplified methods based on manual thermally-assisted hydrolysis and methylation (THM) GC and GC × GC with flame ionization detection (FID) were developed for the detection of mycobacteria and Mycobacterium tuberculosis (MTB) in sputum. A central composite design was employed to optimize the THM derivatization conditions. For the detection of MTB the known mycobacterial markers tuberculostearic acid (TBSA) and hexacosanoic acid (C26), as well as three MTB specific markers, the mycocerosates, were evaluated. We found that the optimum conditions for THM release of TBSA and C26 differ from those for maximum release of the mycocerosates. Higher reagent volumes, higher temperatures and longer incubation increase the mycocerosates yield. Application of these conditions unfortunately resulted in unacceptable safety hazards. A GC × GC-FID method was developed that allowed accurate detection of mycocerosates even at poor conversion yields of the derivatization reaction. Using spiked sputum samples from non-TB patients, the detection limit of the method based on TBSA and C26 was found to be comparable to that of microscopy, i.e. 104-105 bacteria/mL sputum. To validate the new test, we compared the results we found for fifteen sputum samples from patients from South Africa suspected of having tuberculosis with those of culture, the gold standard method. Based on the presence of TBSA and C26, all eight microscopy and culture positive samples, and even two microscopy negative but culture positive samples were positive by THM-GC-FID. All five microscopy and culture negative sputum samples were also negative for THM-GC-FID, giving a specificity of 100%. Using GC × GC-FID we could detect mycocerosates, the specific markers for MTB in seven out of ten MTB culture positive sputum samples. The five culture negative cases were also negative for mycocerosates in manual THM-GC × GC-FID giving again 100% specificity. The results obtained indicate that the new methods hold great potential for the early diagnosis of TB in developing countries.


Assuntos
Cromatografia Gasosa/métodos , Testes Diagnósticos de Rotina/métodos , Mycobacterium tuberculosis/isolamento & purificação , Tuberculose Pulmonar/diagnóstico , Cromatografia Gasosa/instrumentação , Ácidos Graxos/análise , Ácidos Graxos/metabolismo , Humanos , Limite de Detecção , Mycobacterium tuberculosis/química , Mycobacterium tuberculosis/metabolismo , Sensibilidade e Especificidade , Escarro/microbiologia , Ácidos Esteáricos/análise , Ácidos Esteáricos/metabolismo , Tuberculose Pulmonar/microbiologia
11.
J Environ Sci Health B ; 54(8): 717-727, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31230521

RESUMO

The use of shipping containers for cargo transportation has the potential to transport insect pests from infested to non-infested areas. Therefore, fumigation is required as an appropriate biosecurity measure to exterminate these pests. In-transit fumigation trials were conducted in two 20 ft shipping containers during a two-day journey in both September and December 2017. Ethyl formate (90 g m-3) was purged with nitrogen (EF + N2) into the containers. Ethyl formate concentration inside containers and the surrounding environment were monitored at timed intervals throughout the journey. Fumigation achieved sufficient concentration × time (Ct) products in the containers during the journey, which can exterminate all stages of most common insect pests. The Ct products in-transit were greater than those in a shipping container being fumigated in a stationary position at a dose rate of 90 g m-³ for 24 hours exposure. Levels of EF in the environment between 1-15 m downwind from the containers and driver's cabin were less than 0.5 ppm at each of the timed intervals, 200 times below 100 ppm of EF Threshold Limit Value (TLV). Our study indicates that in-transit EF + N2 technology has the potential to deliver cost savings in the fumigation process through reduction of the Labor cost, elimination of the time a container and cargo must remain stationary in a fumigation yard and a significant decrease in total supply chain time (between container packing and receival).


Assuntos
Ésteres do Ácido Fórmico , Fumigação/métodos , Controle de Insetos/métodos , Animais , Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Ésteres do Ácido Fórmico/administração & dosagem , Ésteres do Ácido Fórmico/análise , Fatores de Tempo
12.
J Sep Sci ; 42(11): 2032-2043, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30938053

RESUMO

Liquid microextraction employing solidification of the floating organic droplet, with vortexing and heating to optimize extraction efficiency, was developed for the determination of seven insecticides in fruit juice, vegetables, and agricultural runoff water. The extracts were analyzed by gas chromatography with both flame ionization and mass spectrometry detection for the determination of chlorpyrifos, prothiofos, profenofos, ethion, λ-cyhalothrin, permethrin, and cypermethrin, respectively. Using 20 µL of 1-undecanol in 10 mL of aqueous solution containing 1% w/v sodium chloride provided preconcentration factor of 500. The enrichment factor of the analytes was in the range of 355 to 509 with extraction recovery >71%. The linearity ranges were 4-200 µg/kg for gas chromatography with flame ionization detection and 1-100 µg/kg for gas chromatography with mass spectrometry, with limits of detection ranging from 0.04 to 1.2 µg/kg, which are lower than the international maximum residue limits for vegetables and fruit juice. Intra-day and inter-day precisions are less than 5.4 and 7.0% relative standard deviation, respectively. The method was successfully applied to the determination of the seven insecticides in samples of vegetables, fruit juice and agricultural runoff, with recoveries ranging from 61.7 to 120.8%. The extraction method is simple, efficient and environmentally friendly.


Assuntos
Cromatografia Gasosa/métodos , Sucos de Frutas e Vegetais/análise , Inseticidas/química , Inseticidas/isolamento & purificação , Microextração em Fase Líquida/métodos , Espectrometria de Massas/métodos , Cromatografia Gasosa/instrumentação , Ionização de Chama , Contaminação de Alimentos/análise , Nitrilos/análise , Nitrilos/isolamento & purificação , Piretrinas/análise , Piretrinas/isolamento & purificação
13.
J Chromatogr A ; 1599: 247-252, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-31030953

RESUMO

Thermal desorption aerosol gas chromatography (TAG) is an effective tool for in situ analysis of particulate organic molecules. However, the performance of current TAG is limited by the detectability of low volatile compounds and the matrix effect. In this study, a dual-trap TAG system was developed to address these issues. Thermally desorbed effluent is focused by a weakly retained trap (for low volatile compounds) in a 1 m capillary column conditioned in the GC oven, followed by a strongly retained trap (for high volatile compounds). Then, the focused analytes are desorbed in a reverse flow into the GC column for analysis. Detection over a wide volatility range from C10 to C40 n-alkanes is achieved using the dual-trap TAG. We show that it has lower discrimination of injection, better linearity and higher detectability of n-alkanes. The dual-trap TAG was applied for in-situ measurement of ambient fine particles (PM2.5) in Beijing. Repeatable retention time of n-alkanes was demonstrated during a continuous measurement over two weeks.


Assuntos
Cromatografia Gasosa/instrumentação , Monitoramento Ambiental/métodos , Aerossóis/química , Alcanos/análise , Pequim , Temperatura Alta , Material Particulado/análise , Volatilização
14.
J Chromatogr A ; 1599: 223-230, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-31000208

RESUMO

This work presents the investigation of two triptycene-based materials (TP-3OB and TP-3Im) as the stationary phases for gas chromatographic (GC) separations. The TP-3OB and TP-3Im capillary columns fabricated by static coating exhibited column efficiency of 3000-3500 plates/m for n-dodecane at 120 °C. Also, their McReynolds constants and Abraham system constants were determined to characterize their polarity and molecular interactions with analytes. On the basis of the unique 3D TP architecture, the TP-3OB and TP-3Im stationary phases exhibited complementary high-resolution performance for analytes of a wide ranging polarity, including alkylbenzenes, alkylnaphthalenes, halobenzenes, phenols and anilines, respectively. Moreover, the TP-based columns exhibited good repeatability and reproducibility on the retention times of analytes with the relative standard deviation (RSD) values in the range of 0.01-0.14% for run-to-run, 0.11-0.47% for day-to-day and 0.68-4.7% for column-to-column, respectively. Additionally, their applications for the determination of isomer impurities in the commercial reagents of o-dichlorobenzene, p-/m-diethylbenzene, o-toluidine and 2,3-/3,5-xylidine proved their good potential for practical analysis. This work demonstrates the promising future of the triptycene-based stationary phases for chromatographic separations.


Assuntos
Antracenos/química , Técnicas de Química Analítica/métodos , Cromatografia Gasosa , Alcanos/isolamento & purificação , Compostos de Anilina/química , Cromatografia Gasosa/instrumentação , Isomerismo , Fenóis/química , Reprodutibilidade dos Testes
15.
Environ Sci Pollut Res Int ; 26(2): 1558-1564, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30443721

RESUMO

Alpha-cypermethrin (α-cypermethrin), an important chiral pyrethroid insecticide, is frequently detected in human samples. Because of the possible human health risks caused by α-cypermethrin, we studied dynamics, residues, and metabolism of α-cypermethrin in five common vegetables (tomato, cucumber, rape, cabbage, and pepper) on enantiomeric levels after foliar spray. α-Cypermethrin was qualified by a HP-5 column and its enantiomers could be separated by gas chromatograph (GC) using a BGB-172 chiral column. The results of degradation showed that α-cypermethrin dissipated rapidly in vegetables with half-lives being only 2.85-8.88 days. Stereoselective degradation was observed on pepper and cucumber while the two metabolites (cis-DCCA and 3-PBA) of α-cypermethrin were not detected during its dissipation in all plants. This is the first evidence of enantioselective degradation of α-cypermethrin in the five common vegetables and the results should be considered in future environmental risk and food safety evaluations.


Assuntos
Inseticidas/metabolismo , Piretrinas/metabolismo , Verduras/metabolismo , Biodegradação Ambiental , Brassica/efeitos dos fármacos , Brassica/metabolismo , Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Cucumis sativus/efeitos dos fármacos , Cucumis sativus/metabolismo , Contaminação de Alimentos , Meia-Vida , Inseticidas/química , Lycopersicon esculentum/efeitos dos fármacos , Lycopersicon esculentum/metabolismo , Piretrinas/química , Estereoisomerismo , Verduras/efeitos dos fármacos
16.
J Chromatogr A ; 1584: 179-186, 2019 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-30553504

RESUMO

We report here gas-liquid partition constants and activity coefficients for thirty-seven volatile organic solutes in ionic liquid trihexyl(tetradecyl)phosphonium dicyanamide measured by gas-liquid chromatography using capillary columns. Four capillary columns with exactly known phase ratios were constructed and employed to measure the solute retention factors at four temperatures between 313.15 and 343.15 K. The partition coefficients were calculated from the slopes of the linear regression between solute retention factors and the reciprocal of phase ratio at a given temperature. The partition coefficients thus calculated are free from errors due to the contribution to retention from gas-liquid interphase adsorption. For these reason, reliable solute's infinite dilution activity coefficients can be obtained, as well as partition enthalpies and entropies. A thorough discussion of the uncertainties of the experimental measurements and the main advantages of the use of capillary columns to acquire the aforementioned relevant thermodynamic information was performed.


Assuntos
Eletrocromatografia Capilar/métodos , Cromatografia Gasosa/métodos , Compostos Organofosforados/análise , Compostos Orgânicos Voláteis/análise , Cromatografia Gasosa/instrumentação , Termodinâmica
17.
J Biosci Bioeng ; 127(1): 121-127, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30072117

RESUMO

Many volatile compounds, such as isoprene, a precursor used in the synthesis of natural rubber, have been produced through fermentation using genetically engineered microorganisms. Despite this biotechnological success, measuring the concentrations of volatile compounds during fermentation is difficult because of their high volatility. In current systems, off-line analytical methods usually lead to product loss, whereas on-line methods raise the production cost due to the requirement of complex devices. Here, we developed a novel on-line gas chromatography (GC)-based system for analyzing the concentration of isoprene with the aim to minimize the cost and requirement for devices as compared to current strategies. In this system, a programmable logic controller is used to combine conventional GC with a syringe pump module (SPM) directly connected to the exhaust pipe of the fermentor, and isoprene-containing samples are continuously pumped from the SPM into the GC using an air cylinder recycle stream. We showed that this novel system enables isoprene analysis during fermentation with convenient equipment and without the requirement of an expensive desorption tube. Furthermore, this system may be extended to the detection of other volatile organic compounds in fermentation or chemical processes.


Assuntos
Eletrocromatografia Capilar , Fermentação/fisiologia , Compostos Orgânicos Voláteis/química , Compostos Orgânicos Voláteis/metabolismo , Aerobiose , Reatores Biológicos , Butadienos/química , Butadienos/metabolismo , Eletrocromatografia Capilar/instrumentação , Eletrocromatografia Capilar/métodos , Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Cromatografia Gasosa-Espectrometria de Massas/instrumentação , Cromatografia Gasosa-Espectrometria de Massas/métodos , Hemiterpenos/química , Hemiterpenos/metabolismo , Borracha/química , Volatilização
18.
Electrophoresis ; 40(4): 521-529, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30580436

RESUMO

The easy shrinkage and swelling of polymer monolithic column when exposed to mobile phase with different polarity is a problem that cannot be ignored. To overcome this drawback, a convenient aqueous two-phase polymerization approach was used to prepare poly (polyethylene glycol diacrylate, PEGDA) monolithic porous layer open tubular (mono-PLOT) columns (150 µm). The poly(PEGDA) mono-PLOT column with homogeneous polymer porous layer was synthesized successfully. A maximum plate number of 41,500 plates per meter for allyl thiourea was obtained under a velocity of 1.8 mm/s. Several kinds of polar molecule were separated on the proposed mono-PLOT column and a typical hydrophilic interaction retention mechanism was observed. High speed separation of benzoic acids was also carried out, baseline separation of five benzoic acids was successfully achieved within 5 min with a 70 cm mono-PLOT column at 50°C. Furthermore, the resulting PLOT column was also successfully applied to separate standard analytes of three DNA oxidative damage products and RNA-modified nucleosides and four chlorophenols. At last, the column could separate alcohols, alkanes, and aromatic isomers via GC. It had more than 20,000 plates per meter for butanol - higher than commercial coatings open tubular columns.


Assuntos
Cromatografia Gasosa/instrumentação , Cromatografia Líquida/instrumentação , Polietilenoglicóis/química , Cromatografia Gasosa/métodos , Cromatografia Líquida/métodos , Interações Hidrofóbicas e Hidrofílicas , Modelos Lineares , Modelos Químicos , Compostos Orgânicos/análise , Compostos Orgânicos/química , Compostos Orgânicos/isolamento & purificação , Polimerização , Porosidade , Reprodutibilidade dos Testes
19.
Chemosphere ; 215: 57-61, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30312917

RESUMO

Dihalobenzoquinones are a group of disinfection byproducts with high potential toxicity and thus currently receiving increased attention. A determination method of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ) was developed upon using liquid-liquid extraction and a gas chromatography with an electronic capture detector (LLE-GC-ECD). The optimized extraction condition was as the following: volume ratio of formic acid to water 0.005%, Na2SO4 dosage 200 g L-1, methyl-tert-butyl ether (MtBE)/water volume ratio 1/10, and extraction with MtBE for once. With the dosed concentrations of 0.5-5.0 µg L-1, the recovery rates of 2,6-DCBQ and 2,6-DBBQ were 81%-88% and 73%-96%. The limits of quantitation (LOQs) of the LLE-GC-ECD method were 2.4 and 2.7 ng L-1 in 1-L water for 2,6-DCBQ and 2,6-DBBQ. In six local tap waters, 2,6-DCBQ was detected in the range of

Assuntos
Benzoquinonas/análise , Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Elétrons , Hidrocarbonetos Halogenados/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Benzoquinonas/química , Desinfecção , Hidrocarbonetos Halogenados/química , Poluentes Químicos da Água/química
20.
J Chromatogr A ; 1577: 72-81, 2018 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-30348497

RESUMO

The development of the reversed fill/flush modulator represents a significant advancement in flow-modulated, comprehensive two-dimensional gas chromatography (GC × GC). Compared to the forward flush/fill modulator, the reversed-flow modulator is less susceptible to baseline anomalies and peak tailing as a result of modulator channel overfilling or insufficient purging of high concentration analytes. Flow reversal requires the addition of a bleed capillary not present in the forward-flow modulator. Selecting the appropriate restriction of the bleed capillary is critical. If the bleed capillary is too restrictive, eluate from the first-dimension column can split between the modulator channel and second-dimension column, which also results in baseline artifacts. To gain a better understanding of the reversed-flow modulator, a comprehensive pneumatic model was developed. The model was validated by comparing calculated and measured hold-up times. The errors in calculated hold-up times were less than 1% of the measured values. The model can be used to predict first-dimension eluate splitting and determine the optimal bleed capillary dimensions to prevent its occurrence. Calculation of the modulator hold-up time can be used to determine the maximum collection time to ensure comprehensive analysis and optimal flush times for partial fill operation.


Assuntos
Cromatografia Gasosa/instrumentação , Cromatografia Gasosa/métodos , Modelos Teóricos , Reprodutibilidade dos Testes
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