RESUMO
This work reports a study on the use of Pressurized Liquid Extraction (PLE) for the selective extraction of organic compounds (aliphatic hydrocarbons - AHs, polycyclic aromatic hydrocarbons - PAHs and polycyclic aromatic compounds - PACs) from high-ash Brazilian coal. A homemade PLE system was built and solvents of different polarities (hexane, toluene and ethanol) were employed to extract the organic compounds from coal samples at a pressure of 10 MPa, under temperatures of 80°C and 200°C and extraction times up to 120 min. The selectivity of the extraction process was evaluated by a well-established methodology employed for the characterization of coal extracts (Preparative Liquid Chromatography - PLC 8). The fractions obtained in the PLC-8 method were dried and, after, quantified by gravimetry. Results showed that the proposed method of extraction was selective for the extraction of AHs using hexane at the temperature of 80°C and for the extraction of PAHs at 200°C. Additionally, the method showed to be selective for the extraction of PACs using ethanol at both studied temperatures. The AHs and PAHs fractions were also analyzed by GC-MS, showing that the first was composed mainly by low molecular weight compounds (<31 carbons) while the second by pyrenes, fluoranthenes, crysenes, benzopyrenes, perylenes and benzofluoranthenes. The present method showed to be a powerful tool for selective extraction of organic compounds from coal samples with simplicity, low quantity of solvent and filling other the requirements to be considered a greener method of extraction.
RESUMO
The determination of residues and contaminants in complex matrices such as in the case of food, environmental, and biological samples requires a combination of several steps to succeed in the aimed goal. At least three independent steps are integrated to provide the best available situation to deal with such matrices: (1) a sample preparation technique is employed to isolate the target compounds from the rest of the matrix; (2) a chromatographic (second) step further "purifies" the isolated compounds from the co-extracted matrix interferences; (3) a spectroscopy-based device acts as chromatographic detector (ideally containing a tandem high-resolution mass analyzer) for the qualitative and quantitative analysis. These techniques can be operated in different modes including the off-line and the on-line modes. The present report focus the on-line coupling techniques aiming the determination of analytes present in complex matrices. The fundamentals of these approaches as well as the most common set ups are presented and discussed, as well as a review on the recent applications of these two approaches to the fields of bioanalytical, environmental, and food analysis are critically discussed.