Eiution characteristics of fatty acid methyl esters on capillary columns

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Abstract
The elution characteristics of fatty acid methyl esters on support‐coated and open tubular capillary columns were investigated using reference standards and natural mixtures of fatty acid methyl esters. Over an extended range of fatty acid methyl esters chain lengths (C‐11–C‐26), the plot of the log of the adjusted retention time, t′R, vs. number of carbon atoms in the fatty acid chain was not linear, as has been previously assumed by many investigators. With support‐coated open tubular columns and with diethylene glycol succinate as the stationary phase, the relationship between the log of the retention time and carbon number was best approximated by a second‐order equation: log (t′R)x=α+β(CNx)+γ(CNx)2 where α, β, and γ are the virial coefficients of the equation. In addition, for the longer fatty acid methyl esters, the plots all tended to converge. Hence, for data from capillary columns, especially over a wide range of carbon numbers, all tentative indications based upon linear log plots and parallel lines for different homologous series of fatty acid isomers should be viewed with caution. A method is presented for identifying peaks from capillary columns; it uses quadratic equations and three reference fatty acid methyl ester standards for each homologous series being studied.

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