The syringyl/guaiacyl ratio was determined for six different Eucalyptus spp. wood clones cultivated in four regions in Brazil. The determinants were made by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the results were compared with those obtained by alkaline nitrobenzene oxidation method. The S/G ratios were obtained considering all the identified lignin derivatives in the pyrograms and also using two groups of markers. The first group of markers consisted of guaiacol, 4-methylguaiacol, 4-vinylguaiacol, trans-isoeugenol, syringol, 4-methylsyringol, 4-vinylsyringol and trans-4-propenylsyringol compounds as markers. The second group included guaiacol, 4-methylguaiacol, 4-vinylguaiacol, vanillin, 4-ethylsyringol, 4-vinylsyringol, syringaldehyde, syringylacetone and trans-4-propenylsyringol. It was observed from the statistical analysis that the values of S/G obtained by Py-GC-MS using the two groups of markers did not differ significantly from those obtained by nitrobenzene oxidation method.

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Recebido em 8/2/08; aceito em 2/9/08; publicado na web em 15/4/09 MATRIX EFFECT IN PESTICIDE QUANTIFICATION BY GAS CHROMATOGRAPHY. The lack of accuracy of a chromatographic method can be associated with the matrix effect. This effect is observed in pesticide quantification by gas chromatography when the chromatographic signals of standards prepared in solvents are compared with those of the analyte in extracts of complex matrices. In the competition between the matrix components and the pesticides for the active sites of the liner, a larger amount of pesticides is transferred to the column, giving apparent extractions above 100%. In this work, we discuss factors that contribute to the matrix effect and present some attempts to overcome the problem.