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1.
J Chromatogr A ; 1641: 461994, 2021 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-33676112

RESUMO

A new approach of characterizing the specific properties of 4-(trans-4'-n-alkylcyclohexyl) benzoates, based on the interaction of the acidic and basic testing substances, for their form Crystalline, Smectic B and Nematic have been proposed. The testing substances selected for our study have been considered in the light of the results obtained in the previous research and the data available in the literature for other liquid crystals with different structures. The DN values denoting the electron donor number in the Gutmann scale and the AN* values indicating the acceptor number in the Riddle-Fowkes scale have been chosen in the estimation of the electron acceptor parameter KA and electron donor parameter KD values. The temperature-dependent quotients of KA to KD are employed for the assessment of the electron donor-acceptor properties of 4-(trans-4'-n-alkylcyclohexyl) benzoates. The 4-(trans-4'-n-alkyl cyclohexyl) benzoates tested have the affinity to act as a donor of electrons concerning electron acceptor of the testing substance. The sizes and shapes effects of the testing substances (or penetrants) and the LCs tested (or solvents while in mesophases) are taken into account. The inverse gas chromatography tests were supported by the Quantitative Structure-Activity Relationship modelling technique to determine which part (or group) of liquid crystals tested was dominant in the interaction with the testing substances.


Assuntos
Benzoatos/química , Cromatografia Gasosa/métodos , Cicloexanos/química , Elétrons , Cristais Líquidos/química , Cloreto de Metileno/química , Relação Quantitativa Estrutura-Atividade , Solventes/química , Temperatura
2.
Methods Mol Biol ; 2278: 87-100, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33649950

RESUMO

The biological significance of conjugated fatty acids (CFAs) has been linked to positive health effects based on biomedical, in vitro, and clinical studies. Of note, conjugated linoleic acids (CLAs) are the most widely characterized fatty acids as geometric isomers cis-9,trans-11 and trans-10,cis-12 CLA occur naturally in ruminant fats, dairy products, and hydrogenated oils. Concerning CLAs, it is known that bacterial biohydrogenation, a process whereby ruminal bacteria or starter cultures of lactic acid bacteria have the ability to synthesize CLA by altering the chemical structure of essential fatty acids via enzymatic mechanisms, produces a multitude of isomers with desirable properties. Bifidobacterium species are classed as food grade microorganisms and some of these strains harness molecular determinants that are responsible for the bioconversion of free fatty acids to CLAs. However, molecular mechanisms have yet to be fully elucidated. Reports pertaining to CLAs have been attributed to suppressing tumor growth, delaying the onset of diabetes mellitus and reducing body fat in obese individuals. Given the increased attention for their bioactive properties, we describe in this chapter the qualitative and quantitative methods used to identify and quantify CLA isomers produced by bifidobacterial strains in supplemented broth media. These approaches enable rapid detection of potential CLA producing strains and accurate measurement of fatty acids in biological matrices.


Assuntos
Bifidobacterium/metabolismo , Ácidos Linoleicos Conjugados/metabolismo , Bifidobacterium/química , Técnicas de Cultura de Células/métodos , Cromatografia Gasosa/métodos , Isomerismo , Ácidos Linoleicos Conjugados/análise , Espectrofotometria/métodos
3.
J Chromatogr A ; 1641: 461983, 2021 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-33611124

RESUMO

One of the main causes for the sparse use of multivariate analytical methods in routine laboratory work is the dependency on the measuring instrument from which the analytical signal is acquired. This issue is especially critical in chromatographic equipment and results in limitations of their applicability. The solution to this problem is to obtain a standardized instrument-independent signal -or instrument-agnostic signal- regardless of the measuring instrument or of the state of the same instrument from which it has been acquired. The combined use of both internal and external standard series, allows us to have external and transferable references for the normalization of both the intensity and the position of each element of the data vector being arranged from the raw signal. From this information, a simple mathematical data treatment process is applied and instrument-agnostic signals can be secured. This paper describes and applies the proposed methodology to be followed for obtaining standardized instrumental fingerprints from two significant fractions of virgin olive oil (volatile organic compounds and triacylglycerols), obtained by gas chromatography coupled to mass spectrometry (GC-MS) and analysed with two temperature conditions (conventional and high-temperature, respectively). The results of both case studies show how the instrument-agnostic fingerprints obtained are coincidental, regardless of the state of the chromatographic system or the time of acquisition.


Assuntos
Cromatografia Gasosa/métodos , Cromatografia Gasosa/normas , Temperatura Alta , Azeite de Oliva/química , Padrões de Referência , Triglicerídeos/análise , Compostos Orgânicos Voláteis/análise
4.
J Chromatogr A ; 1640: 461943, 2021 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-33556678

RESUMO

The effect of a gradient of solute velocity on the chromatographic separation of closely spaced solutes is investigated by usage of a simulation. The concept of the ideal basic separation (IBS), introduced by Blumberg, is used to determine the theoretical limit of a separation without any natural or artificial gradients of features of the chromatographic medium. The IBS is the best achievable separation and can therefore be used as a baseline to which other separations can be compared to. An addition of a negative velocity gradient cannot improve the separation of closely spaced solutes. The velocity gradient is realized by adding a temperature gradient to a GC separation. The simulation confirms this theoretical limit for a range of differently strong retained solutes. In a second part controlled deviations from IBS are used to show, that a velocity gradient can be beneficial in realistic, non-IBS. The addition of a negative velocity gradient can improve e.g. the separation of broad injected solute zones or counteract a positive gradient of the mobile phase velocity caused by gas decompression along the GC column. However, the improved separation cannot exceed that of a corresponding ideal basic separation. The resolution of broadly injected solutes can be increased by up to 45% of the corresponding IBS resolution by adding a negative velocity gradient. A positive velocity gradient due to gas decompression reduces the separation by up to 6%. The added negative velocity gradient, realized by a linear temperature gradient, can compensate this resolution loss by up to 2%.


Assuntos
Cromatografia Gasosa/métodos , Simulação por Computador , Temperatura
5.
J Chromatogr A ; 1639: 461894, 2021 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-33497832

RESUMO

Inverse gas chromatography was employed to investigate the sorption and diffusion of hydrocarbons into polydimethylsiloxane (PDMS) in the headspace-solid phase microextraction (HS-SPME) sampling process. Six hydrocarbons as molecular probes and two types of non-cross-linked PDMS with different average molecular weights as stationary phases were used in this study. Experimental measurements with columns containing a PDMS stationary phase were carried out to obtain specific retention volumes, molar enthalpies of sorption, interaction parameters, diffusion coefficients, and activation energies of diffusion of hydrocarbon probes over temperatures ranging from 60 to 90°C. The primary driving force of the hydrocarbon sorption into the PDMS SPME fibers was found to be the molar enthalpy of sorption, which depended on the molecular size of the hydrocarbons. As the molecular size of the hydrocarbon increased, the molar enthalpies of sorption became more exothermic. Interaction parameters and diffusion coefficients indicated that both n-heptane and n-octane were diffused into the PDMS matrix and localized to form clusters or aggregates, which were responsible for more negative molar entropies of sorption. However, the diffusivities of n-nonane and aromatic probes were limited due to their large molecular size and lack in the structural flexibility, respectively. The molar enthalpies of hydrocarbon sorption were independent of the average molecular weight of PDMS. However, specific retention volumes, interaction parameters, diffusion coefficients, and activation energies of diffusion of the hydrocarbons depended on the molecular weight of PDMS as well as the molecular weights and structures of hydrocarbons, as shown by the results of the Wilcoxon signed-rank test.


Assuntos
Cromatografia Gasosa/métodos , Dimetilpolisiloxanos/química , Hidrocarbonetos/análise , Microextração em Fase Sólida/métodos , Adsorção , Difusão , Peso Molecular , Temperatura
6.
Nat Protoc ; 16(2): 1152-1169, 2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-33432233

RESUMO

Chemical space is vast, and chemical reactions involve the complex interplay of multiple variables. As a consequence, reactions can fail for subtle reasons, necessitating screening of conditions. High-throughput experimentation (HTE) techniques enable a more comprehensive array of data to be obtained in a relatively short amount of time. Although HTE can be most efficiently achieved with automated robotic dispensing equipment, the benefits of running reaction microarrays can be accessed in any regularly equipped laboratory using inexpensive consumables. Herein, we present a cost-efficient approach to HTE, examining a Buchwald-Hartwig amination as our model reaction. Experiments are carried out in a machined aluminum 96-well plate, taking advantage of solid transfer scoops and pipettes to facilitate rapid reagent transfer. Reaction vials are simultaneously heated and mixed, using a magnetic stirrer, and worked up in parallel, using a plastic filter plate. Analysis by gas chromatography provides the chemist with 96 data points with minimal commitment of time and resources. The best-performing experiment can be selected for scale-up and isolation, or the data can be used for designing future optimization experiments.


Assuntos
Ensaios de Triagem em Larga Escala/métodos , Aminação/fisiologia , Catálise , Fenômenos Químicos , Cromatografia Gasosa/métodos
7.
J Am Soc Mass Spectrom ; 32(4): 860-871, 2021 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-33395529

RESUMO

Masks constructed of a variety of materials are in widespread use due to the COVID-19 pandemic, and people are exposed to chemicals inherent in the masks through inhalation. This work aims to survey commonly available mask materials to provide an overview of potential exposure. A total of 19 mask materials were analyzed using a nontargeted analysis two-dimensional gas chromatography (GCxGC)-mass spectrometric (MS) workflow. Traditionally, there has been a lack of GCxGC-MS automated high-throughput screening methods, resulting in trade-offs with throughput and thoroughness. This work addresses the gap by introducing new machine learning software tools for high-throughput screening (Floodlight) and subsequent pattern analysis (Searchlight). A recursive workflow for chemical prioritization suitable for both manual curation and machine learning is introduced as a means of controlling the level of effort and equalizing sample loading while retaining key chemical signatures. Manual curation and machine learning were comparable with the mask materials clustering into three groups. The majority of the chemical signatures could be characterized by chemical class in seven categories: organophosphorus, long chain amides, polyethylene terephthalate oligomers, n-alkanes, olefins, branched alkanes and long-chain organic acids, alcohols, and aldehydes. The olefin, branched alkane, and organophosphorus components were primary contributors to clustering, with the other chemical classes having a significant degree of heterogeneity within the three clusters. Machine learning provided a means of rapidly extracting the key signatures of interest in agreement with the more traditional time-consuming and tedious manual curation process. Some identified signatures associated with plastics and flame retardants are potential toxins, warranting future study to understand the mask exposure route and potential health effects.


Assuntos
Cromatografia Gasosa/métodos , Manufaturas/análise , Máscaras , Espectrometria de Massas/métodos , Automação Laboratorial , Humanos , Exposição por Inalação/prevenção & controle , Modelos Químicos , Compostos Orgânicos/análise , Polímeros/análise , Segurança , Software
8.
Food Chem ; 347: 129030, 2021 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-33515968

RESUMO

A modified quick, easy, cheap, effective, rugged, and safe (QuEChERs) method for determining triazine herbicide residues in bivalves (Mussels, Scallops, Cockles) was developed. The use of molecularly imprinted polymers (MIPs) as a selective purification material during dispersive-solid phase extraction (d-SPE) increased the removal rate of pigments interference. With 4% acidic acetonitrile as the organic modifier, the modified QuEChERs method achieved good extraction rate of herbicide residues. The satisfactory recoveries (80%-118%) and RSDs (1.0%-11.6%) of herbicide residues were obtained at three spiked levels. The limits of quantification of herbicide residues ranged from 0.10 µg/kg to 1.59 µg/kg. Further, the herbicide residues in bivalves collected in the eastern coasts of China was analyzed. The developed QuEChERs procedure coupled with GC-MS/MS was successfully applied to the herbicide residues detection in bivalves, and due to the extensive use of herbicides and the large consumption of bivalves in globally, the ongoing risk evaluation is needed.


Assuntos
Bivalves/química , Resíduos de Praguicidas/análise , Extração em Fase Sólida/métodos , Triazinas/análise , Animais , China , Cromatografia Gasosa/métodos , Herbicidas/análise , Espectrometria de Massas em Tandem/métodos , Triazinas/isolamento & purificação
9.
Food Chem ; 346: 128924, 2021 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-33429297

RESUMO

The increasing interest of consumers in the still-developing craft beer market and the strict tax-related legal regulations concerning alcoholic beverages require precise methods for quality control. Determination of ethyl alcohol concentration was performed in 167 samples of alcoholic beverages (craft beers, soft drinks, wines, and cider). We applied headspace gas chromatography using a dual column/dual flame ionization detector (HS-GC-FID/FID), a technique routinely used in forensic toxicology. The method was linear in range, from 0.01 to 20.0%, with a coefficient of determination of 0.999 (R2). The limit of quantification was 0.01%; the detection limit was 0.003%. Furthermore, very good validation parameters were achieved (precision and accuracy below 5%). The samples were analyzed for compliance with EU standards and recommendations of The Beer Judge Certification Program. Moreover, the content of trace quantities of volatile compounds and fusel alcohols (1-propanol, 2-propanol, acetone, and acetaldehyde) was found in the majority of alcoholic beverages.


Assuntos
Cerveja/análise , Bebidas Gaseificadas/análise , Cromatografia Gasosa/métodos , Etanol/análise , Análise de Alimentos/métodos , Vinho/análise , Ionização de Chama , Humanos
10.
J Chromatogr A ; 1638: 461882, 2021 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-33453657

RESUMO

This paper reported a headspace gas chromatography (HS-GC) for the determination of denitrifying enzyme activity in soil samples. It was based on measuring the NO2 signal in a set of closed/air-free vials containing soil samples that incubated at the designated conditions. The results showed that the method has a good measurement precision (RSD < 5.0%) and reasonable accuracy for determining the denitrifying enzyme activity in soil samples. It is simple and efficient, and very suitable to be used in batch sample analysis.


Assuntos
Cromatografia Gasosa/métodos , Desnitrificação , Enzimas/metabolismo , Solo/química , Calibragem , Dióxido de Nitrogênio/análise , Tamanho da Amostra , Fatores de Tempo
11.
J Chromatogr A ; 1636: 461792, 2021 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-33340747

RESUMO

Chiral metal-organic cages (MOCs) are a new type of porous materials with unique molecular recognition ability, which have received research attention as a chiral stationary phase (CSP) for gas chromatography (GC). Herein, we report the detailed investigation of a chiral MOC ([Cu12(LPA)12(H2O)12], PA = L-phenylalanine, MOC-PA) as a novel stationary phase for GC separations. The MOC-PA capillary column exhibited a high-resolution performance for a wide range of analytes, including n-alkanes, n-alcohols, esters, aromatic compounds and the Grob mixture, positional isomers and racemates. In particular, MOC-PA coated column displayed good resolution and performance for amino acid derivatives. Moreover, the MOC-PA column showed excellent separation repeatability and reproducibility. The relative standard deviation (RSD) values for the retention times were in the range of 0.16-0.30% for run to run (n = 3), 0.31-0.77% for day-to-day (n = 3), and 3.6-4.7% for column-to-column (n = 3), respectively. The experimental results showed that MOC-PA had great potential as a GC stationary phase.


Assuntos
Cromatografia Gasosa/métodos , Metais/química , Compostos Orgânicos/química , Álcoois/química , Alcanos/química , Ésteres/química , Fenilalanina/química , Reprodutibilidade dos Testes , Espectroscopia de Infravermelho com Transformada de Fourier , Estereoisomerismo , Termogravimetria , Difração de Raios X
12.
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
13.
Food Chem ; 338: 127712, 2021 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-32829295

RESUMO

Herein, a new method for quantifying the brominated vegetable oil content in commercial soft drinks was developed, which accelerated the sample preparation process and improved analytical efficiency. First, simple and accurate chromatographic separation techniques were performed using a VF-5ht column for both GC-FID (quantitative) and APGC-QTOF (qualitative) analyses. The samples were subjected to chromatography on a reversed-phase solid-phase extraction cartridge. (PoraPak™RxnRP). Transesterification using a boron trifluoride methanol complex in methanol solution was performed. When validating this method, the analyte recovery percentages were between 82.2% and 99.9%, and the recovery and standard deviation of repeatability values were between 1.2% and 3.5%. Using an isotope library, the bromostearic acid methyl esters (9,10-dibromostearic acid methyl ester, 9,10,12,13-tetrabromostearic acid methyl ester, and hexabromostearic acid methyl ester) in the sample mixtures were qualitatively confirmed via APGC-QTOF. A novel aqueous ammonium adduct, which has not been previously reported, was also confirmed. These results indicated that this new method was simple, accurate, and also allowed for precise qualitative and quantitative confirmation as well as high reproducibility.


Assuntos
Bebidas Gaseificadas/análise , Cromatografia Gasosa/métodos , Cromatografia Gasosa-Espectrometria de Massas/métodos , Óleos Vegetais/química , Ionização de Chama , Halogenação , Óleos Vegetais/isolamento & purificação , Reprodutibilidade dos Testes , Extração em Fase Sólida
14.
J Chromatogr A ; 1637: 461837, 2021 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-33383237

RESUMO

The conversion of waste streams into a useable material through a recycling process is a hot topic. Waste streams can originate from domestic and industrial sources and range from plastic waste to medical waste to various industrial waste streams, both solid and liquid. In addition to waste circularity, circularity for bio-based waste streams and renewable sources are also being investigated. To simplify this complexity, this article presents a case study evaluating the output from the feedstock recycling of plastic waste originating from municipal solid waste. Plastic waste entering the environment is undesired, and many initiatives are working towards a plastics circular economy. Once disposed of, ideally, plastic waste should be either re-used or recycled in order to avoid incineration or disposal in landfills. Recycling waste plastic can occur either via mechanical recycling or feedstock (chemical) recycling, where feedstock recycling can occur for example, through gasification or pyrolysis technologies. This article will focus only on the oils obtained from the pyrolysis of mixed waste plastic. The output from pyrolysis has a different composition than traditional fossil-based hydrocarbon streams, and therefore, must be evaluated to correctly process as feedstock. The authors have previously shown that gas chromatography coupled to vacuum ultraviolet detection (GC-VUV) provides accurate identification and quantification of the hydrocarbon composition (paraffins, isoparaffins, olefins, naphthenes, and aromatics - PIONA) of fossil-based liquid hydrocarbon streams.1 Therefore, GC-VUV was evaluated for analysis of the pyrolysis oils from plastic waste. Using an in-house modified spectral library in combination with the PIONA+ software, accurate identification and quantification of the hydrocarbon composition of pyrolysis oils from C4 through C30+ was possible with a limit of detection of 0.1 wt.%. To the best of our knowledge, this article is the first example of accurate PIONA-type quantification of pyrolysis oils by GC-VUV.


Assuntos
Cromatografia Gasosa/métodos , Óleos/química , Plásticos/química , Pirólise , Resíduos Sólidos/análise , Alcenos/análise , Hidrocarbonetos/análise , Reprodutibilidade dos Testes
15.
J Chromatogr A ; 1632: 461596, 2020 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-33045497

RESUMO

Despite nearly 80 years of advancements in gas chromatography (GC), indirect chemical matrix effects (MEs), known as the matrix-induced response enhancement effect, still occur to cause a high bias in the GC analysis of susceptible analytes, unless precautions are taken. Matrix-matched calibration is one common option used in GC to compensate for the MEs, but this approach is usually inconvenient, imprecise, and inefficient. Other options, such as the method of standard additions, surface deactivation techniques, chemical derivatizations, priming the GC, and/or use of internal standards, also have flaws in practice. When methods are accommodating, the use of analyte protectants (APs) can provide the best practical solution to not only overcome MEs, but also to maximize analyte signal by increasing chromatographic and detection efficiencies for the analytes. APs address the source of MEs in every injection by filling active sites in the GC inlet, column, and detector, particularly in GC-MS, rather than the analytes that would otherwise undergo degradation, peak tailing, and/or diminished response due to interactions with the active sites. The addition of an adequate amount of APs (e.g. sugar derivatives) to all calibration standards and final extracts alike often leads to lower detection limits, better accuracy, narrower peaks, and greater robustness than the other options to compensate for MEs in GC. This article consists of a critical review of the scientific literature, proposal of mechanisms and theory, and re-evaluation studies involving APs for the first time in GC-orbitrap and GC-MS/MS with a high-efficiency ion source design. The findings showed that 1 µg each of co-injected shikimic acid and sorbitol in the former case, and 1 µg shikimic acid alone in the latter case, led to high quality results in multi-residue analysis of pesticides and environmental contaminants.


Assuntos
Cromatografia Gasosa/métodos , Calibragem , Cromatografia Gasosa-Espectrometria de Massas , Publicações , Processamento de Sinais Assistido por Computador
16.
J Chromatogr A ; 1632: 461604, 2020 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-33080532

RESUMO

Fine-tuning of the SiF62--containing metal-organic frameworks (SIFSIX) through the substitution of metal centers and ligands changed the apertures from 8.3 Å to 3.8 Å, resulting in ultramicropores and notably improving the separation performance of alkane isomers. Herein, we reported SIFSIX-1-Zn, SIFSIX-1-Cu and SIFSIX-3-Zn as representative stationary phases for capillary gas chromatography (GC). The capillary column coated with ultramicroporous SIFSIX-3-Zn efficiently separated the alkane isomers and benzene homologues, which outperformed SIFSIX-1-Zn and SIFSIX-1-Cu. This resulted from size matching between the window of the ultramicroporous SIFSIX-3-Zn and the analytes, which was also supported by McReynolds constants, column efficiency and peak tailing effect. It opened up a new avenue for ultramicroporous materials in the chromatography separation of isomers.


Assuntos
Cromatografia Gasosa/métodos , Estruturas Metalorgânicas/química , Alcanos/química , Benzeno/química , Isomerismo , Porosidade
17.
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
18.
J Chromatogr A ; 1627: 461372, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823089

RESUMO

This paper demonstrated the non-validity of Schultz et al. method by proving that the surface areas of n-alkanes and polar molecules strongly depend of the temperature. Consequently, the results of surface properties obtained by this method are inaccurate. Inverse gas chromatography (IGC) at infinite dilution and the dynamic contact angle (DCA) technique were used on the polytetrafluoroethylene (PTFE) fibers. DCA measurements led to the determination of the surface energy γs(T) of PTFE fibers as a function of the temperature T (Relation 6). The variations of the surface areas of n-alkanes and polar molecules versus the temperature were determined by studying the same PTFE fibers by IGC at infinite dilution. We proved that the product of the surface area a(T, Cn) (in Å2) of an alkane by the dispersive component of the surface energyγsd(T)of the solid is constant at any temperature: [Formula: see text] , where b(Cn) is a constant only depending on the carbon atom number n of n-alkane Cn. An analytical relation of the surface area of n-alkanes as a function of the temperature was obtained (equation 18). Our results highlighted the failure of Dorris-Gray method that was largely used to determine γsd of solids. This method considered the surface area a-CH2- of methylene group equal to 6 Å2 and constant for any used temperature. The obtained results proved the non-validity of Dorris-Gray method and gave the expression of a-CH2- as a function of the temperature T (Equation 20) proved the non-validity of Dorris-Gray method. The calculations of the thermal expansion coefficients of the surface area a and radius R represented by the respective derivatives da/dT and dR/dT, showed their important variations as a function of the temperature. The general expression of the surface area aX(T) of polar molecules was given as a function of the temperature (Expression 48). The large effect of the temperature on surface areas and radii of molecules was highlighted, except for toluene. The surface area of toluene was proved to remain constant whatever the temperature. Our results showed, in general, non-linear variations of the radius rX(T) of polar molecules adsorbed on PTFE fibers. However, except for chloroform, dichloromethane and diethyl ether where their thermal expansion coefficient depends on the temperature, the linearity of rX(T) was verified in the temperature interval [293 K, 353 K].


Assuntos
Cromatografia Gasosa/métodos , Modelos Moleculares , Compostos Orgânicos/análise , Temperatura , Adsorção , Alcanos/análise , Politetrafluoretileno/análise , Dióxido de Silício/química , Propriedades de Superfície
19.
J Chromatogr A ; 1627: 461396, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823101

RESUMO

Comprehensive two-dimensional gas chromatography (GC×GC) based on flow-modulation (FM) is gaining increasing attention as an alternative to thermal modulation (TM), the recognized GC×GC benchmark, thanks to its lower operational cost and rugged performance. An accessible, rational procedure to perform method translation between the two platforms would be highly valuable to facilitate compatibility and consequently extend the flexibility and applicability of GC×GC. To enable an effective transfer, the methodology needs to ensure preservation of the elution pattern, separation power, and sensitivity. Here, a loop-type thermal modulation system with dual detection (TM-GC×GC-MS/FID) used for the targeted analysis of allergens in fragrances is selected as reference method. Initially, six different columns configurations are systematically evaluated for the flow-modulated counterpart. The set-up providing the most consistent chromatographic separation (20 m x 0.18 mm dc x 0.18 µm df + 1.8 m x 0.18 mm dc x 0.18 µm df) is further evaluated to assess its overall performance in terms of sensitivity, linearity, accuracy, and pattern reliability. The experimental results convincingly show that the method translation procedure is effective and allows successful transfer of the target template metadata. Additionally, the FM-GC×GC-MS/FID system is suitable for challenging applications such as the quantitative profiling of complex fragrance materials.


Assuntos
Cromatografia Gasosa/métodos , Alérgenos/análise , Calibragem , Cromatografia Gasosa/normas , Ionização de Chama , Limite de Detecção , Perfumes/análise , Perfumes/normas , Reprodutibilidade dos Testes
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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