Comparação entre métodos de quantificação em cromatografia gasosa: um experimento para cursos de química

This article describes an experiment designed to teach quantitative determination in gas chromatography (GC) in Organic and Analytical Chemistry practical classes. The experiment consisted of extracting and analyzing eugenol from clove seeds to perform a quantitative approach aimed at comparing results obtained by external and internal calibration procedures. Therefore, this experiment proved to be very effective tool to enhance students awareness on the need to understand different types of calibration in GC and on how to avoid common experimental errors, and to find the best ways to eliminate their interference during the quantitative analysis phase.

Composição molecular e origem paleobotânica de âmbares da bacia do Araripe, Formação Santana

The terpenoid composition of seven amber samples from Araripe Basin (Santana Formation, Crato Member) has been analyzed by gas chromatography-mass spectrometry to determine their botanical origin. The diterpenoids, which have been identified in the fossil resin extracts are derived primarily from the abietane class, e.g., dehydroabietane, 4-epidehydroabietol, 16,17,18-trisnorabieta-8,11,13-triene, 7-oxo-16,17,19-trisnorabieta-8,11,13-trieno, dehydroabietic acid, ferruginol, hinokiol and hinokione. Their composition is certainly typical for conifers, and angiosperms can be excluded as the botanical source, as no triterpene was identified. The terpenoid characteristics strongly support a relationship to the Araucariaceae or Podocarpaceae families. In addition, the fossil record of the embedding sediments (pollen and fossil leaves) also supports the proposal of these paleobotanical origins for the ambers.

Comparação de diferentes abordagens para avaliação da incerteza na cromatografia gasosa do gás natural

The evaluation of uncertainty associated with an analytic result is an essential part of the measurement process. Recently, several approaches to evaluate the uncertainty in measurement have been developed. Here, the gas chromatography assay uncertainty for natural gas is compared by some of these approaches: the guide to the expression of uncertainty in measurement (GUM) approach, top-down approach (reproducibility estimate from an inter-laboratory study), Barwick & Ellison (data from validation), study of variability and fuzzy approach. The comparison shows that GUM, Barwick & Ellison and fuzzy approaches lead to comparable uncertainty evaluations, which does not happen with the top-down approach and study of variability by the absence of data normality.

Determinação de resíduos de pesticidas em plasma bovino por cromatografia gasosa-espectrometria de massas

An analytical method for the isolation based on matrix solid-phase dispersion technique and gas chromatographic determination of pesticides in cattle plasma is presented. It was fortified 0.25 g of plasma with pesticides and blended with 1 g each C18 and Na2SO4. The homogenized matter was transferred to a SPE cartridge, which contained 1 g of activated florisil with 5 mL acetonitrile. The analites were eluted under vaccum with 15 mL acetonitrile, the extract was analyzed by gas chromatography-mass spectrometry. The limit of quantification of the method was 0.04 mg L-1 for chlorphenvinfos and fipronil and 0.02 mg L-1 for cypermethrin..

Teores de compostos orgânicos em cachaças produzidas na região norte fluminense - Rio de Janeiro

This work aimed to quantify some organic compounds in "cachaças" (sugar cane spirit). The ethyl alcohol was quantified by densimetry, after distillation. The acetic acid, methyl alcohol, n-propyl alcohol, n-butyl alcohol, isobutyl alcohol, isoamyl alcohol (mixture of 2-methyl-butyl and 3-methyl-butyl), ethyl acetate and acetaldehyde were determined by gas chromatography; and the furfural, 5-hydroxy-methylfurfural and acrolein by high efficiency liquid chromatography. From the 30 samples analyzed, 63.3% showed non-conformity with national legislation regarding at least one of the analyzed components.

Determinação de etanol e voláteis relacionados em sangue e fluido oral por microextração em fase sólida em headspace associada à cromatografia gasosa com detector de ionização em chama

The aim of this study was to validate a method for the determination of acethaldehyde, methanol, ethanol, acetone and isopropanol employing solid-phase microextraction associated to gas chromatography with flame ionization detection. The operational conditions of SPME were optimized by response surface analysis. The calibration curves for all compounds were linear with r² > 0.9973. Accuracy (89.1-109.0%), intra-assay precision (1.8-8.5%) and inter-assay precision (2.2-8.2%) were acceptable. The quantification limit was 50 µg/mL. The method was applied to the meaurement of ethanol in blood and oral fluid of a group of volunteers. Oral fluid ethanol concentrations were not directly correlated with blood concentrations.

Determinação de citrato de sildenafila e de tadalafila por cromatografia líquida de ultraeficiência com detecção por arranjo de diodos (CLUE-DAD)

A simple ultra-performance liquid chromatographic method for the simultaneous determination of sildenafil citrate and tadalafil was developed and validated. Sample preparation was dissolution in methanol, followed by centrifugation and dilution (1:10) with methanol. Analysis was performed in an Acquity® UPLC system with Acquity® BEH C18 column (2.1 x 50 mm, with 1.7 μm particles). The elution was isocratic with phosphate buffer pH 2.3 and acetonitrile (65:35, v/v) at a flow rate of 0.7 mL/min. The method presented adequate specificity, linearity, precision and accuracy and allowed the determination of the drugs in seized forensic samples.

Hidrólise do óleo de Azadirachta indica em água subcrítica e determinação da composição dos triacilglicerídeos e ácidos graxos por cromatografia gasosa de alta resolução a alta temperatura e cromatografia gasosa de alta resolução acoplada à espectrometria de massas

The development of modern analytical tools plays an important role in quality control. The main purpose of this study was to explore the use of subcritical water as a versatile analytical tool, employed simultaneously as a reagent and solvent, as well as the application of high temperature-high resolution gas chromatography (HT-HRGC) to develop a procedure for the analysis of triacylglycerides and fatty acids in Azadirachta indica A. Juss. (Neem) oil without the need for solvents, chemical reagents, or catalytic agents. The developed method presented satisfactory results and is in agreement with the concepts of Green Analytical Chemistry (GAC).

Desenvolvimento de métodos analíticos para determinação de agrotóxicos em sedimentos por cromatografia gasosa monodimensional e bidimensional abrangente com micro detector de captura de elétrons

The development of analytical methods for determination of eight pesticides of different chemical classes (trichlorfon, propanil, fipronil, propiconazole, trifloxystrobin, permethrin, difenoconazole and azoxystrobin) in sediments with gas chromatography-micro-electron capture detector (GC/µECD) and comprehensive two-dimensional gas chromatography with micro-electron capture detector (GCxGC/µECD) is described. These methods were applied to real sediment samples, and the best results were obtained using a 5% diphenyl-methylpolysiloxane column for 1D-GC. For GCxGC the same column was employed in the first dimension and a 50%-phenyl-methylpolysiloxane stationary phase was placed in the second dimension. Due to the superior peak capacity and selectivity of GCxGC, interfering matrix peaks were separated from analytes, showing a better performance of GCxGC.

Determinação do teor de ésteres graxos em biodiesel metílico de soja por cromatografia gasosa utilizando oleato de etila como padrão interno

A method for ester content determination in soybean methyl biodiesel was studied, using ethyl oleate as internal standard. A biodiesel sample was analyzed and had its purity estimated as 92.8%. Method accuracy was evaluated by comparison with the result obtained via EN14103, with a relative difference of 0.1%. Repetitivity and intermediate precision were estimated as 2 and 1.5%, respectively.

MSPD procedure combined with GC-MS for the determination of procymidone, bifenthrin, malathion and pirimicarb in honey

A method based on matrix solid-phase dispersion and gas chromatography-mass spectrometry to determine procymidone, malathion, bifenthrin and pirimicarb in honey is described. The best results were obtained using 1.0 g of honey, 1.0 g of silica-gel as dispersant sorbent and acetonitrile as eluting solvent. The method was validated by fortified honey samples at three concentration levels (0.2, 0.5 to 1.0 mg kg-1). Average recoveries (n=7) ranged from 54 to 84%, with relative standard deviations between 3.7 and 8.5%. Detection and quantification limits attained by the developed method ranged from 0.02 to 0.08 mg kg-1 and 0.07 to 0.25 mg kg-1 for the honey, respectively.

Desenvolvimento de metodologia para determinação de piretroides em manteiga

The objective of this study was to evaluate the use of the matrix solid-phase dispersion technique associated with purification at low temperature for the determination of pyrethroids in butter. Evaluated parameters included: sample/adsorbent ratio, type of adsorbent and extractor solvent. The optimized method was validated based on predetermined requirements. The detection limits of the pyrethroids cypermethrin and deltamethrin were 0.082 and 0.11 μg g-1, and quantification limit were 0.28 and 0.32 μg g-1, respectively, with extraction percentages near 90% and coefficients of variation less than of 10%..

Determinação do coeficiente de atividade em diluição infinita de hidrocarbonetos em furfural a 298,15 K por SPME-GC/FID

In this work a new method (SPME-GC/FID) was developed to analyze the activity of binary liquid mixtures. The purpose is to demonstrate that SPME is capable to be used to determinate activity coefficients at infinite dilution knowing the fiber properties, with a lower cost than the conventional methods encountered in literature such as GLC. The activity coefficients at infinite dilution in furfural for n-hexane, n-heptane and cyclohexane at 298.15 K was determined using SPME and deviations of literature data was about 7%.

Ácidos orgânicos em aguardentes produzidas em alambique e em coluna

The concentration of 14 organic acids of 50 sugarcane spirits samples was determined by gas chromatography using flame ionization detection. The organic acids analytical quantitative profile in stills and column distilled spirits from wines obtained from the same must were compared. The comparison was also carried in "head", "heart" and "tail fractions of stills distilled spirits. The experimental data were analyzed by Principal Components Analysis (PCA) and pointed out that the distillation process (stills and column) strongly influences the lead spirits' organic acid composition and that producers' operational "cuts off" to produce "tail", "heart" and "head", fractions should be optimized.

Aplicação de métodos quimiométricos na caracterização de charutos utilizando extração por dispersão da matriz em fase sólida e análise por cromatografia gasosa acoplada à espectrometria de massas

In this work, the organic compounds of cigar samples from different brands were analyzed. The compound extraction was made using the matrix solid-phase dispersion (MSPD) technique, followed by gas chromatography and identification by mass spectrometry (GC-MS) and standards, when available. Thirty eight organic compounds were found in seven different brands. Finally, with the objective of characterizing and discriminating the cigar samples, multivariate statistical analyses were applied to data, e.g.; principal component analysis (PCA) and hierarchical cluster analysis (HCA). With such analyses, it was possible to discriminate three main groups of three quality levels.