El gradiente de temperatura en el análisis cuantitativo de ácidos grasos de muy elevada masa molecular por cromatografía gaseosa capilar y de relleno

Abstract

The specific mass response (Rim) of each compound and the relationship between such response and that of the Internal Standard used, parameter known as mass response factor (fim) are important factors in quantitative determinations performed by gas chromatography (GC), defining the accuracy of results. The influence of temperature gradient on Rim and fim during the analysis of very longchain fatty acids methyl esters with odd carbon atoms (C20:0-C30:0), using C19:0 as internal standard was studied. A packed column with impregnated stationary phase and a wide-bore capillary column with bonded stationary phase were used. Two studies were carried out, the first one studied the variation of temperature gradient (5, 10, 15 and 20 ºC/min), and the second one was an accuracy assay by applying the method of standard addition. Results showed that when the packed column was used, the fim value increased with the molecular mass; while for each acid such value tended to decrease as the temperature gradient increased. However, when capillary column was used, fim values for all acids were similar and close to the theoretical ones, regardeless of the changes in the temperature gradient. Also, Rim values were greater than those obtained with the packed column. In spite of the variations of Rim observed for the packed column, the use of the internal standard method, previous calculation of the fim, allowed accurate quantitative determination using both columns.