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1.
Food Chem ; 334: 127601, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-32712491

RESUMO

Quantitative labeling of oil compositions has become a trend to ensure the quality and safety of blended oils in the market. However, methods for rapid and reliable quantitation of blended oils are still not available. In this study, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used to profile triacylglycerols in blended oils, and partial least squares regression (PLS-R) was applied to establish quantitative models based on the acquired MALDI-MS spectra. We demonstrated that this new method allowed simultaneous quantitation of multiple compositions, and provided good quantitative results of binary, ternary and quaternary blended oils, enabling good limits of detection (e.g., detectability of 1.5% olive oil in sunflower seed oil). Compared with the conventional GC-FID method, this new method could allow direct analysis of blended oils, analysis of one blended oil sample within minutes, and accurate quantitation of low-abundance oil compositions and blended oils with similar fatty acid contents.


Assuntos
Análise de Alimentos/métodos , Óleos Vegetais/análise , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/métodos , Cromatografia Gasosa/métodos , Ácidos Graxos/análise , Análise de Alimentos/estatística & dados numéricos , Contaminação de Alimentos/análise , Análise dos Mínimos Quadrados , Azeite de Oliva/análise , Óleos Vegetais/química , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/estatística & dados numéricos , Óleo de Girassol/análise , Triglicerídeos/análise
2.
Food Chem ; 336: 127729, 2021 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-32768914

RESUMO

The roles of lipid oxidation substrates and muscle microstructure in lipid oxidation were investigated in two muscle models (cod and pig). Added myoglobin (Mb) promoted lipid oxidation in washed cod muscle (WCM) but not in washed pig muscle (WPM). The differing microstructure of WCM e.g. more exposed fat cells or membrane of muscle cells compared to the "denseness" or "wrapped" structure of WPM, may have contributed to the better ability of Mb to facilitate lipid oxidation in the WCM. Added phospholipids with polyenoic indexes of 282 and 24 activated Mb as an oxidant similarly in WPM while added neutral lipids and added free fatty acids had little effect. It is suggested that muscle microstructure and accessibility of Mb to phospholipids play critical roles in relation to Mb-mediated lipid oxidation while the degree of unsaturation in the phospholipids was less important.


Assuntos
Gadiformes/metabolismo , Lipídeos/química , Músculos/metabolismo , Mioglobina/química , Animais , Cromatografia Gasosa , Peroxidação de Lipídeos , Lipídeos/análise , Suínos , alfa-Tocoferol/análise
3.
Chemosphere ; 262: 127477, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32799136

RESUMO

Focus on the safety of herbal medicines has mainly been directed towards the presence of intrinsic toxicity, as found in the cases of renal and hepatic dysfunction caused by aristolochic acids. However, contamination from extrinsic hazards may impart an even greater reduction in their safety and efficacy. This study reveals that pesticides were present in the majority (88%) of a comprehensive cross-section (n = 1771) of herbal medicine samples. Alarmingly, more than half (59%) contained pesticides over the European Pharmacopoeia (EP) limit, and 43% of them contained 35 varieties of banned, extremely toxic pesticides, eight of which were detected at levels over 500 times higher than the default Maximum Residue Limit (MRL). DDTs, carbofuran, and mevinphos were confirmed as being among the most risk-inducing pesticides by three different risk assessment methods, reported to produce carcinogenic, genotoxic, reproductive, and developmental effects, in addition to carrying nephrotoxicity and hepatotoxicity. In light of these findings, and withstanding that extrinsic hazards can be controlled unlike intrinsic toxicity, the authors here strongly recommend the application of herbal medicine quality-control measures and solutions to safeguard against a neglected but certainly potentially serious health risk posed to the majority of the global population that consumes herbal medicines.


Assuntos
Contaminação de Medicamentos , Medicamentos de Ervas Chinesas/análise , Praguicidas/análise , Carbofurano , Cromatografia Gasosa , Cromatografia Líquida/métodos , Cromatografia Gasosa-Espectrometria de Massas/métodos , Humanos , Resíduos de Praguicidas/análise , Medição de Risco , Espectrometria de Massas em Tandem/métodos
4.
Food Chem ; 335: 127664, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-32739820

RESUMO

Odor-taste interaction has become a popular salt reduction method. In this study, the odorants associated with saltiness in soy sauce were selected by gas chromatography/olfactometry-associated taste (GC/O-AT), and their ability to induce saltiness/umami enhancement was verified by sensory evaluation. A total of 30 taste-associated odorants were perceived, including 5 saltiness-associated and 2 umami-associated odorants. Among them, 3-(methylthio)propanal, 1-octen-3-ol, 3-(methylthio)-1-propanol, and 2,5-dimethylpyrazine could significantly enhance saltiness of 0.3% NaCl solution (p < 0.05). Furthermore, 3-(methylthio)propanal, maltol, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (HDMF), dimethyl trisulfide, 3-(methylthio)-1-propanol and 1-octen-3-ol could also enhance the umami taste in 0.3% monosodium glutamate solution. Compared with zero or strong-salt-content (0.8%) solution, the saltiness of weak-salt-content (0.3%) was enhanced significantly by adding the odorant. These results suggest that salty food is an efficient source for selecting saltiness-enhancing odorants, which could be used to compensate NaCl reduction in food.


Assuntos
Odorantes/análise , Alimentos de Soja/análise , Paladar , Adulto , Cromatografia Gasosa , Feminino , Análise de Alimentos/métodos , Humanos , Masculino , Octanóis , Olfatometria , Pirazinas , Cloreto de Sódio na Dieta/análise , Glutamato de Sódio , Compostos Orgânicos Voláteis/análise , Adulto Jovem
5.
AAPS PharmSciTech ; 21(7): 286, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-33063151

RESUMO

The CoViD-19 pandemic has caused a sudden spike in demand and production of hand sanitisers. Concerns are rising regarding the quality of such products, as the safeguard of consumers is a priority worldwide. We analyse here the ethanolic content of seven off-the-shelf hand sanitiser gels (two biocides and five cosmetics) from the Italian market, using gas chromatography. The WHO recommends that products containing ethanol should have 60-95% (v/v) alcohol. Four of the tested hand gels have ethanolic contents within the recommended range, while three products (all cosmetics) contain < 60% (v/v), i.e. 52.1% (w/w), ethanol. The product with the lowest alcoholic content has 37.1% w/w ethanol. Toxic methanol is not found in any of the hand sanitisers. We show, in addition, that products with the highest ethanolic content have generally greater antibacterial activity. In conclusion, all tested products are complying with the EU regulations, as the three "substandard" products are classified as cosmetics, whose purpose is cleaning and not disinfecting. Nevertheless, if such hand cleaners were inappropriately used as hand disinfectants, they might be ineffective. Thus, consumer safety relays on awareness and ability to distinguish between biocidal and cosmetics hand gels. The obtained results might sensitise the scientific community, health agencies and ultimately consumers towards the risks of using hand sanitisers of substandard alcoholic concentration. If the wrong product is chosen by consumers, public health can be compromised by the inappropriate use of "low-dosed" cosmetic gels as disinfectants, particularly during the period of the CoViD-19 pandemic.


Assuntos
Infecções por Coronavirus , Higienizadores de Mão/análise , Pandemias , Pneumonia Viral , Antibacterianos/análise , Antibacterianos/farmacologia , Bactérias/efeitos dos fármacos , Cromatografia Gasosa , Cosméticos , Escherichia coli/efeitos dos fármacos , Etanol/análise , Europa (Continente) , Géis , Desinfecção das Mãos , Higienizadores de Mão/farmacologia , Higienizadores de Mão/normas , Metanol/análise , Testes de Sensibilidade Microbiana , Staphylococcus aureus/efeitos dos fármacos
6.
J Environ Qual ; 49(5): 1110-1125, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33016464

RESUMO

Certain aspects in the collection, handling, storage, and subsequent analysis of discrete air samples from non-steady-state flux chambers are critical to generating accurate and unbiased estimates of nitrous oxide (N2 O) fluxes. The focus of this paper is on air sample collection and storage in small vials (<12 ml) primarily for gas chromatography (GC) analysis. Sample integrity is assured through following simple procedures including storage under pressure and analysis within a few months of collection. Concurrent storage of standards in an identical manner to samples is recommended and allows the storage period to be reliably extended. In the laboratory, an autosampler is typically used in batch analysis of ∼200 sequentially analyzed samples by GC with an electron capture detector (ECD). Some comparisons are given between GC and alternatives including optical N2 O detectors that are increasingly being used for high-precision N2 O measurement. The importance of calibration and traceability of gas standards is discussed, where high-quality standards ensure the most accurate assessment of N2 O concentration and comparability between laboratories. The calibration allows a consistent and best estimate of flux to be derived.


Assuntos
Óxido Nitroso , Calibragem , Cromatografia Gasosa
7.
J Oleo Sci ; 69(11): 1381-1388, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33055451

RESUMO

The oil content and the fatty acid composition of roasted and unroasted melon seed and oils were determined. The oil contents of roasted melon seeds changed between 26.4% (Type 12) and 38.7% (Type 4). In general, oil contents of roasted melon seeds were found higher than that of unroasted seeds that could be due to the evaporation of water during roasting processes which consequently lead to increased concentrations of other seed components including oils. Saturated fatty acid contents of unroasted melon seed samples change between 13.5% (Type 6) and 17.1% (Type 20). In addition, polyunsaturated fatty acids of unroasted melon seed oils ranged from 51.9% (Type 13) to 70.2% (Type 6). Palmitic acid contents of roasted seed oils varied between 7.8% (Type 5) and 15.1% (Type 17). In addition, the oleic acid contents ranged from 15.4% (Type 10) to 37.7% (Type17). Also, linoleic acid contents were found between 34.7% (Type 17) and 70.3% (Type 6). Saturated fatty acid contents of roasted melon seed oils ranged from 13.5% (Type 6) to 16.7% (Type 13). The major tocopherols in both roasted and unroasted melon seed oils were α-tocopherol, É£-tocopherol and δ-tocopherols. Melon seed oils are rich in linoleic, oleic acids and É£-tocopherol.


Assuntos
Culinária , Cucurbitaceae/química , Ácidos Graxos Insaturados/análise , Ácidos Graxos/análise , Temperatura Alta , Óleos Vegetais/química , Sementes/química , Tocoferóis/análise , Cromatografia Gasosa , Cromatografia Líquida de Alta Pressão , Ácido Linoleico/análise , Ácido Oleico/análise , Ácido Palmítico/análise
8.
J Chromatogr A ; 1633: 461627, 2020 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-33128970

RESUMO

A Poly (3,4-ethylenedioxothiophene) (PEDOT)/UiO-66 composite was electrodeposited on an etched stainless-steel wire as head-space solid-phase microextraction (HS-SPME) coating. A robust, well controlled thickness, and uniform coating of metal organic framework composites can be realized by the electrodeposited strategy. The incorporated UiO-66 not only enhanced the uniformity and stability of the composite coating, but also effectively decreased the stacking phenomenon of PEDOT and improved its extraction efficiency, which was over 100 times higher than that of the PEDOT coating without UiO-66. The composite coating was used to enrich seven types of volatile organic compounds (VOCs) in ion-exchange resins, including methyl cyclohexane, benzene, toluene, ortho-xylene, styrene, para-xylene and divinyl-benzene. The results of adsorption isotherm analysis showed that π stacking effect played dominant role between the composite coating and VOCs in the extraction process. The composite coating was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared and thermogravimetric analysis, respectively. A determination method for seven kinds of VOCs was established by HS-SPME coupled with gas chromatography-flame ionization detection (GC-FID). Under the optimal experimental conditions, the detection linear range (LRs) was 0.09-100 ng mL-1, and the detection limit (LODs) was 0.03-0.06 ng mL-1 (S/N = 3). The method was applied for the migration detection of VOCs in four types of ion-exchange resin, which showed satisfactory recovery (84.5-117.2%).


Assuntos
Técnicas de Química Analítica/métodos , Estruturas Metalorgânicas/química , Polímeros/química , Tiofenos/química , Compostos Orgânicos Voláteis/isolamento & purificação , Adsorção , Benzeno/análise , Benzeno/isolamento & purificação , Cromatografia Gasosa , Ionização de Chama , Resinas de Troca Iônica/química , Limite de Detecção , Microextração em Fase Sólida , Aço Inoxidável/química , Tolueno/análise , Tolueno/isolamento & purificação , Compostos Orgânicos Voláteis/análise , Xilenos/análise , Xilenos/isolamento & purificação
9.
Artigo em Chinês | MEDLINE | ID: mdl-32892597

RESUMO

Objective: To establish a gas chromatography method for detecting isobutyl methacrylate in workplace air. Methods: From July to October 2019, isobutyl methacrylate in workplace air was collected by activated charcoal tube, absorbed using carbon disulfide and analyzed by gas chromatography (FID) with FFAP capillary column. Results: The linear range of isobutyl methacrylate in the method was 0-800 µg/ml, the correlation coefficient was 0.99993. The detection limit was 0.35 µg/ml. The lowest detected concentration was 0.12 mg/m(3). The within-run precision was 2.06%-2.72%, the between-run precision was 3.03%-3.83%. The rates of desorption was 96.7%. The breakthrough volume was 14.46 mg. The average sampling efficience was 100%. The samples could be stored at room temperature for 7 days. Conclusion: The method is simple, highly sensitive and precise. Isobutyl methacrylate in workplace air could be determined accurately.


Assuntos
Poluentes Ocupacionais do Ar/análise , Cromatografia Gasosa , Ácidos Polimetacrílicos/análise , Dissulfeto de Carbono , Monitoramento Ambiental , Metacrilatos , Local de Trabalho
10.
PLoS One ; 15(9): e0238921, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32925944

RESUMO

The objective of this study was to characterize the chemical composition and lipid profile of colostrum and milk of purebred Quarter Horse mares. Thirty-four (34) purebred mares were selected, which were then separated into groups according to age, birth order and lactation stage. Colostrum samples were collected in the first six hours after delivery and milk samples from the 7th postpartum day, with intervals of 14 days until the end of lactation. The samples were refrigerated and sent to the Milk Laboratory of the University (Laboleite-UFRN), where they were analyzed for chemical composition. Colostrum was assessed by refractometry. The lipid profile was determined by gas chromatography through a separation of methyl esters. The data were tabulated and subjected to descriptive statistics and analysis of variance by the F-Test, and the groups were compared by the Tukey test using a significance level of 5%. There was high protein content and reduced lactose content for the colostrum of the Quarter Horse mares, differing from other breeds. The milk composition was not influenced by the mares' age. However, variations in the lactation stage and in the birth order of the Quarter Horse mares altered the milk's chemical composition. There is variation in the lipid composition of milk according to the lactation stage, without changing the characteristic profile of the mares' milk or diminishing the nutritional quality of the lipid fraction.


Assuntos
Colostro/química , Lipidômica/métodos , Lipídeos/análise , Leite/química , Animais , Peso Corporal , Cruzamento , Cromatografia Gasosa , Feminino , Cavalos , Valor Nutritivo , Gravidez , Refratometria
11.
Exp Parasitol ; 218: 107984, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32871143

RESUMO

The fascioliasis is a parasitic disease of importance in veterinary medicine and public health. For this parasitosis, the treatment by synthetic fasciolicides is used and due to their intense use although they have been shown less effective because of the establishment of resistant Fasciola hepatica population to these drugs, with a global concern. The use of derived products of plants with biological activity has been shown promising in the control of parasites. In this context, we evaluated the chemical composition and action of ovicidal in vitro fixed oil of Helianthus annuus L. (FOH) and essential oil of Cuminum cyminum L. (EOC), as well as their combination (FOH + EOC) of F. hepatica. In the assay in vitro of F. hepatica were submitted to different concentrations of oils, such as FOH (2.3 mg/mL + 0,017 mg/mL); EOC (2.07 mg/mL + 0,004 mg/mL) and the combination of (1.15 mg/mL + 1.03 mg/mL to 0,0085 mg/mL + 0,008 mg/mL) as well as a positive control of thiabendazole (0.025 mg/mL) and a negative control with distilled water and tween. The identification of the majority chemical compounds was performed by gas chromatography. The -cell viability of the oils was tested in MDBK cellular line by the MTT method. The majority compounds in the FOH were the linoleic (53.6%) and oleic (35.85%) unsaturated fatty acids, and the majority phytochemicals compounds in the EOC were the Cumaldehyde (26.8%) and the 2-Caren 10-al (22.17%). The EOC and the combination presented effectiveness of 99% (±1) and of 94% (±1) in the concentration of 0.03 mg/mL and 0.035 mg/mL+0.03 mg/mL, respectively, and the FOH was insufficiently active as ovicidal. The cell viability at this concentration of EOC was 93%. From the results above we could infer that the EOC is promising as a new alternative for the fascioliasis control.


Assuntos
Cuminum/química , Fasciola hepatica/efeitos dos fármacos , Helianthus/química , Óleos Voláteis/farmacologia , Óleos Vegetais/farmacologia , Análise de Variância , Animais , Anti-Helmínticos/farmacologia , Bovinos , Sobrevivência Celular/efeitos dos fármacos , Cromatografia Gasosa , Cães , Combinação de Medicamentos , Indicadores e Reagentes , Fígado/parasitologia , Células Madin Darby de Rim Canino/efeitos dos fármacos , Óleos Voláteis/química , Óvulo/efeitos dos fármacos , Óleos Vegetais/química , Sais de Tetrazólio , Tiabendazol/farmacologia
12.
J Chromatogr A ; 1628: 461449, 2020 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-32822988

RESUMO

This paper reported a new method for the determination of the water distribution in sludge. It was based on a multiple headspace extraction (MHE) procedure to step-wise remove the water vapor from a closed vial containing a sludge sample, followed by a gas chromatographic measurement (GC). By plotting the GC signal of water vapor vs. the headspace extraction number, three different trend lines from the profile can be observed. From which two transition points can be determined and thus the stages for the free water, capillary water, and adsorption water release can be divided. Based on the sum of GC peak areas ate each stage, the content of these water types in the sludge can be calculated through a method calibration. The results showed that the MHE-GC method has a better measurement repeatability (RSD < 18.6%) and sensitivity (limit of quantitation = 0.028%) than the thermal drying method (used as a reference method). There was also a good agreement between the MHE-GC and the reference method on the free water and capillary water analysis. Moreover, the results on the adsorption water and bound water testing by the present method is more justifiable than the reference method.


Assuntos
Cromatografia Gasosa/métodos , Esgotos/análise , Água/análise , Calibragem , Dessecação , Pressão , Reprodutibilidade dos Testes , Temperatura , Fatores de Tempo
13.
J Chromatogr A ; 1626: 461369, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797848

RESUMO

Pumped sorbent tube sampling is a well established method for the sampling of volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) in ambient, indoor and workplace atmospheres1. Safe sampling volumes and breakthrough volumes have been published for commonly found VOCs on widely used sorbents such as Tenax, however for newer sorbents and less commonly found VOCs there is less robust data. The Safe Sampling Volumes (SSVs) were determined from 15 tests of Retention Volume on 12 VOCs across the 3 sorbents. VOCs tested were: Aldehydes (C5, C6, C8, C9), Ketones (C4, C6), Alcohols (C3, C4), Furan, Limonene, Isoprene and Ethyl Acetate. 12 VOC / sorbent combinations gave SSVs large enough for practical sampling of indoor atmospheres, while SSVs for Furan on Carbopack-X, Isovaleraldehyde on Tenax TA and Methyl Ethyl Ketone on Tenax TA gave SSVs that were too small to be of practical use. This work identifies suitable sorbents and sampling volumes for the complete range of species tested.


Assuntos
Cromatografia Gasosa/métodos , Polímeros/química , Compostos Orgânicos Voláteis/análise , Adsorção , Poluição do Ar em Ambientes Fechados/análise , Aldeídos/química , Monitoramento Ambiental , Furanos/química , Compostos Orgânicos Voláteis/química
14.
J Chromatogr A ; 1626: 461381, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797855

RESUMO

A reliable and sensitive analytical approach has been optimized for the extraction of seven polychlorinated biphenyls (PCBs) from human breast milk. Hollow fiber liquid phase microextraction (HF-LPME) was applied for the first time for the extraction and pre-concentration of the analytes. Analytes were separated by gas chromatography with electron capture detector (GC-µECD) for the sensitive detection and mass spectrometry for the unequivocal identification. A rotable central composite design (RCCD) was performed for the multivariate optimization of the method. The best results were obtained at 40 °C during 30 min and 600 rpm of stirring speed using a hollow fiber length of 5 cm and toluene as an extractant phase and salt addition was not required. The detection limits were in the range 7-14 ng L-1 for PCBs. The coefficients of determination of the calibration curves indicated good linearity (R2> 0.96) and the enrichment factors ranged from 74 to 143. This type of study is of great importance due to the deleterious effect that the presence of contaminants can produce in infants health related to the immature character of the defense system. Moreover, exclusive breastfeeding is recommended by neonatologists up to six months of life and as complementary food during the first two years.


Assuntos
Microextração em Fase Líquida/métodos , Leite Humano/química , Bifenilos Policlorados/análise , Cromatografia Gasosa , Humanos , Concentração de Íons de Hidrogênio , Limite de Detecção , Bifenilos Policlorados/isolamento & purificação , Porosidade , Reprodutibilidade dos Testes , Sais/química
15.
J Chromatogr A ; 1626: 461384, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797857

RESUMO

More and more various chemical media are being applied in enantioseparation; among them, ionic liquids (ILs) have attracted the long-term attention in this decade as green designable solvents. This paper provides comprehensive overview for the applications of ILs in chiral extraction, gas chromatography, liquid chromatography, capillary electrophoresis and other techniques for enantioseparation. Additionally, the important resolution mechanisms based on ILs have also been summarized and discussed. This review focuses on the latest development of enantioseparation methods by using ILs in various modes, leading to meaningful and valuable information to related fields and thus promotes further research and application of reported methods.


Assuntos
Cromatografia Gasosa/métodos , Cromatografia Líquida de Alta Pressão/métodos , Eletroforese Capilar/métodos , Líquidos Iônicos/química , Ligantes , Extração Líquido-Líquido , Extração em Fase Sólida , Estereoisomerismo
16.
Artigo em Chinês | MEDLINE | ID: mdl-32746580

RESUMO

Objective: To develop a solvent desorption-gas chromatography method for determination of trichlorobenzene in workplace air. Methods: Trichlorobenzene in workplace air were captured by Sampling tube consisting of glass fiber filter and solvent desorption activated carbon and desorbed with carbon disulfide, separated through capillary chromatographic column, and then analyzed by gas chromatography-electron capture detector. Results: The linear ranges of 1, 2, 3-trichlorobenzene, 1, 2, 4-trichlorobenzene and 1, 3, 5-trichlorobenzene were 12.20-1220.00, 16.60-1660.00 and 14.80-1480.00 µg/L, respectively, and the related coefficients were between 0.99946 to 0.99948. The relative standard deviations (RSD) within the groups of 1, 2, 3-trichlorobenzene, 1, 2, 4-trichlorobenzene and 1, 3, 5-trichlorobenzene were 1.96%-2.68%, 1.73%-2.82% and 1.81%-2.56%, respectively, and the RSD between the groups were 3.27%-4.25%, 2.85%-4.83% and 3.46%-4.43%, respectively. The average recovery efficiencies were 92.4%, 92.0% and 93.6%, respectively. The minimum quantification concentrations were 0.81, 1.53 and 1.18 µg/m(3), respectively (3 ml desorption solution, 15.00 L sample) . The samples could be stored at room temperature for at least 5 days. Conclusion: This method could be used for monitoring of 1, 2, 3-trichlorobenzene, 1, 2, 4-trichlorobenzene and 1, 3, 5-trichlorobenzene in workplace air.


Assuntos
Poluentes Ocupacionais do Ar/análise , Clorobenzenos/análise , Cromatografia Gasosa , Local de Trabalho , Solventes
17.
J Chromatogr A ; 1629: 461500, 2020 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-32861091

RESUMO

To facilitate faster selectivity evaluation of wall-coated, open-tubular columns using the solvation parameter model a reduced set of calibration compounds is identified and validated for the temperature ranges 60-140 °C and 160-260 °C. The Kennard-Stone uniform mapping algorithm is used to identify the calibration compounds from a larger database of compounds with known retention properties previously adopted for column selectivity evaluation. Thirty-five compounds for each temperature range are required to minimize the standard deviation of the system constants used for selectivity evaluation and to minimize differences between system constants determined by conventional calibration and the reduced calibration compounds. The models for the reduced calibration compounds on ten siloxane-based and poly(ethylene glycol) stationary phases have a coefficient of determination of 0.984 to 0.998 and standard error of the estimate of 0.012 to 0.30. The predictive capability of models is evaluated for the reduced sets of calibration compounds using external test sets with ranking of the calibration models by changes in the average error, average absolute error and root mean square error of prediction for the test sets. For the selected thirty-five reduced calibration compounds the range for the average absolute error was 0.014 to 0.033 and 0.016 to 0.040 for the root mean square error of prediction for the independent test sets.


Assuntos
Cromatografia Gasosa/métodos , Algoritmos , Benzofenonas/análise , Benzofenonas/normas , Calibragem , Cromatografia Gasosa/normas , Polietilenoglicóis/química , Siloxanas/química , Solventes/química , Temperatura
18.
J Chromatogr A ; 1626: 461355, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797835

RESUMO

Quantification of the gas streams from chemical systems such as catalytic reactors are routinely performed by on-line gas chromatography. Gas chromatographs used for this purpose are typically provided with a combination of thermal conductivity (TCD) and flame ionization (FID) detectors to be able to detect and quantify both permanent gases; COx, N2, H2, etc., and hydrocarbons. However, the accuracy of the quantification is hindered by the intrinsic limitations of each type of detector. Namely, TCD has low sensitivity and FID does not detect permanent gases. Therefore, modern gas chromatographs include methanizer units to partially overcome this shortcoming by converting COx to methane. However, as far as these authors know, the literature has not presented an analytical method to characterize gas streams with high accuracy by the simultaneous use of a combination of a TCD-FID detection system provided with a methanizer. This work is an attempt to solve this problematic; it consists of the formulation of a mathematical model for the well-known external and internal standard quantification methods in gas chromatography. The analysis of the gas stream from a catalytic reactor performing the combustion of methane was used to validate the developed method. The concentration ranges of the analysed gases were: 0.8-7.7 vol% of CH4, CO2, and CO, 7.7-38.5 vol.% of O2, and 46.2-90.8 vol.% of N2 at a total flow of 130 mL min-1. It was found that the commonly applied external standard method leads not only to inaccurate quantification but also to physically meaningless carbon balances and conclusions on the behaviour of the selected model system. In contrast, the internal standard method led to a highly accurate quantification with a physically meaningful carbon balance. Considering these findings, this contribution also draws attention to the need for a thoughtful application of chromatographic methods when studying the reactivity of gas systems.


Assuntos
Cromatografia Gasosa/métodos , Gases/análise , Sistemas On-Line , Carbono/análise , Catálise , Ionização de Chama , Metano/análise , Oxigênio/análise , Padrões de Referência , Reprodutibilidade dos Testes , Condutividade Térmica
19.
J Chromatogr A ; 1626: 461342, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797823

RESUMO

GC × GC is an advanced separation technique allowing to achieve quantitative and qualitative characterization of complex samples. In order to perform two-dimensional separation, the system must provide suitable peak modulation which will direct short impulses of first column flow towards the second column. Forward fill/ flush differential flow modulation is a cost effective and no cryogen requiring approach which allows modulation over a wide range of analytes with very different boiling points. However, optimization of the flow modulation process can be difficult to understand and quantification performance might be compromised if the parameters of the modulation process are not properly set. Modulated peak shape can be a good indication of the efficiency of the modulation process, however it is not sufficient to guarantee good quantification. Different average velocities in the beginning and the end of the thermally programmed GC run may cause different efficiency of the modulation process in various parts of the chromatogram. The purpose of this work is to investigate quantitative performance of the forward/fill flush modulation and delineate parameters that determine the effectiveness of the modulation process and its ability to properly reflect the quantitative composition of the investigated sample.


Assuntos
Cromatografia Gasosa/métodos , Modelos Teóricos , Parafina/química , Temperatura
20.
J Chromatogr A ; 1626: 461308, 2020 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-32797813

RESUMO

The Wayne State University (WSU) experimental descriptor database is utilized to bench mark the current capability of the solvation parameter model for use as a quantitative structure-retention relationship tool for estimating retention in gas and reversed-phase liquid chromatography. The prediction error for the retention factors of varied compounds on six open-tubular columns for gas chromatography (Rtx-5 SIL MS, DB-35 ms, RtxCLPesticides, HP-88, HP-INNOWAX and SLB-IL76) and three packed columns for reversed-phase liquid chromatography (SunFire C18, XBridge Shield RP18, and XBridge Phenyl) is used to establish expectations related to current practices. Each column data set was divided into a training set for calibration and a test set for validation employing a roughly 1 to 2 split, such that each test set contained about 40 to 80 varied compounds. The average absolute error for the prediction of retention factors by gas chromatography varied from about 0.1 to 0.4 on the retention factor scale with the larger error typical of stationary phases ranked as the most polar (or cohesive). For reversed-phase liquid chromatography the average error for the prediction of retention factors was 0.3 to 0.5 and generally larger than for gas chromatography. Statistical filters where utilized to identify a group of polycyclic aromatic compounds without hydrogen-bonding functional groups with a larger prediction error on the SunFire C18 column than for other compounds of smaller size, flexible structure or containing hydrogen-bonding functional groups. The heterogeneity of the retention mechanism is speculated to be the main contribution to the prediction error for both gas and liquid chromatography using the solvation parameter model.


Assuntos
Cromatografia Gasosa/métodos , Cromatografia de Fase Reversa/métodos , Ligação de Hidrogênio , Cinética , Solventes/química
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