RESUMEN
Diesel and naphtha samples were analyzed using ionic liquid (IL) columns to evaluate the best column set for the investigation of organic sulfur compounds (OSC) and nitrogen(N)-containing compounds analyses with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry detector (GC×GC/TOFMS). Employing a series of stationary phase sets, namely DB-5MS/DB-17, DB-17/DB-5MS, DB-5MS/IL-59, and IL-59/DB-5MS, the following parameters were systematically evaluated: number of tentatively identified OSC, 2D chromatographic space occupation, number of polyaromatic hydrocarbons (PAH) and OSC co-elutions, and percentage of asymmetric peaks. DB-5MS/IL-59 was chosen for OSC analysis, while IL59/DB-5MS was chosen for nitrogen compounds, as each stationary phase set provided the best chromatographic efficiency for these two classes of compounds, respectively. Most compounds were tentatively identified by Lee and Van den Dool and Kratz retention indexes, and spectra-matching to library. Whenever available, compounds were also positively identified via injection of authentic standards.
Asunto(s)
Cromatografía de Gases y Espectrometría de Masas/métodos , Líquidos Iónicos/química , Compuestos de Nitrógeno/análisis , Petróleo , Compuestos de Azufre/análisis , Brasil , Cromatografía de Gases y Espectrometría de Masas/normas , Hidrocarburos Aromáticos/análisis , Hidrocarburos Aromáticos/química , Compuestos de Nitrógeno/química , Estándares de Referencia , Compuestos de Azufre/químicaRESUMEN
A new material for matrix solid phase dispersion (MSPD) was synthesized -- p-nitro-N-propylaniline/silica (pNNPASi) by grafting reactions, characterized by elemental analysis and N(2)-adsorption-desorption isotherms, and tested for multiclass multiresidue analysis of pesticides in wet and freeze-dried carrots. Results obtained applying this new solid phase sorbent to MSPD extraction of ten pesticides (trichlorphon, trifluralin, dicloran, chlorothalonil, prometryn, linuron, captan, procymidone, prochloraz, and deltametrin) in wet carrots showed better results than the ones obtained for freeze-dried samples. Recoveries were in the range of 48-106% and precisions varied from 6 to 20% when wet samples were employed. Comparison between pNNPASi sorbent and C(18) showed better performance of pNNPASi for eight out of ten pesticides tested. The LOQs show that the developed method can be used to detect the pesticides investigated in carrots at concentrations below the maximum residue levels (MRL) established by EU, USEPA, and National Sanitary Surveillance Agency (ANVISA). Linuron, captan, prochloraz, and deltamethrin were found in at least one of the two commercial samples studied in concentrations above the LOQ of this method. Concentrations of the last three pesticides were above the European MRL in one of the commercial samples.
Asunto(s)
Compuestos de Anilina , Cromatografía/instrumentación , Daucus carota/química , Análisis de los Alimentos/métodos , Plaguicidas/análisis , Dióxido de Silicio , Extracción en Fase Sólida/métodos , Compuestos de Anilina/síntesis química , Compuestos de Anilina/química , Cromatografía/métodos , Humanos , Ensayo de Materiales , Estructura Molecular , Porosidad , Reproducibilidad de los Resultados , Dióxido de Silicio/síntesis química , Dióxido de Silicio/químicaRESUMEN
The objective of this work was to investigate the extraction of Ilex paraguariensis leaves by means of three extraction techniques: pressurized liquid extraction (PLE, also called accelerated solvent extraction--ASE), maceration, and sonication. Samples of mate tea leaves were collected from an experiment conducted under agronomic control at Indfistria e Comércio de Erva-Mate Barão LTDA, Brazil. Six solvents with increasing polarities (n-hexane, toluene, dichloromethane, ethyl acetate, acetone, and methanol) were used in this investigation. Chemical analysis of the extracts was performed by GC coupled with a mass spectrometer detector. The identification and quantification were accomplished by coinjections of certified standards. The results showed that no significant differences in the qualities of the extracts were noticed regarding the extraction methods. On the other hand, the PLE technique was found to be more effective for the extractions of caffeine, phytol, palmitic, and stearic acid. The use of PLE led to a significant decrease in the total extraction time, amount of solvent consumption, and manipulation of samples compared to maceration and ultrasound-assisted extraction methods.
Asunto(s)
Cromatografía de Gases/métodos , Ilex paraguariensis/química , Hojas de la Planta/químicaRESUMEN
A simple method for benzene, toluene, and xylenes (BTX) quantitative analyses in human urine was developed, using headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry detection in the single ion monitoring mode. The developed method is solventless, non-invasive, requires small volume of sample (1 ml), shows high selectivity, sensitivity, repeatability, and linearity (correlation coefficients >0.998), providing a useful alternative to assess human exposure to BTX compounds due to occupational reasons or eventual exposure to organic solvents. Detection limit varies from 0.28 to 0.5 ppb (v/v).
Asunto(s)
Benceno/análisis , Cromatografía de Gases/métodos , Tolueno/orina , Xilenos/orina , Humanos , Exposición Profesional , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
In this work a simple method was described for selective extraction of benzoic acid from landfill leachate samples. The samples were submitted to solid-phase extraction (SPE) with XAD-4 resin as the stationary phase and ion-exchange chromatography (IEC) using the ion-exchange resin Amberlyst A-27. The instrumental analysis was performed by gas chromatography with mass spectrometric detection (GC-MSD). Benzoic acid was isolated, identified and quantified. The extraction process is rapid, simple and of low cost. It was also environmental friendly, that is, it was used a minimum amounts of hazardous organic solvents and produced also minimum quantities of residues.
Asunto(s)
Ácido Benzoico/análisis , Cromatografía de Gases y Espectrometría de Masas/métodos , Resinas de Intercambio IónicoRESUMEN
In this work, preparative liquid chromatography was used for the separation of the nitrogen compounds in a sample of heavy gas oil from a Brazilian petroleum. Initially it took place a pre-fractionation by neutral aluminium oxide and the compounds were separated in different classes such as: hydrocarbons, resins (compounds of low molecular mass and intermediate polarity) and asphalthenes (polar compounds with high molecular mass). A comparison of the fraction of resins was performed by re-fractionating with modified silica (with potassium hydroxide and hydrochloric acid), or with ion exchange resins (Amberlyst A-27 and A-15), being isolated the basic and neutral compounds, that were analyzed by GC-MS in the scan and selected ion monitoring modes. Quinolines, benzoquinolines, tetrahydroquinolines were found in the basic fraction and carbazoles derivatives were found in the neutral fraction.