Determination of the carbon deficiency in the flame ionization detector response of long-chain fatty acid methyl esters and dicarboxylic acid dimethyl esters

Abstract

Carbon deficiencies (CDs) of long-chain fatty acid methyl esters (FAMEs) and dicarboxylic acid dimethyl esters (DDMEs), which lead to decreased response in a flame ionization detection (FID) system, were determined by using full responding hydrocarbons (heptadecane, eicosane and alpha-cholestane) as references. For saturated FAMEs ranging from C 12 to C 22 and for DDMEs ranging from C 4 to C 10, CDs between 1.3 ± 0.12 and 1.7 ± 0.36 per ester group were recorded. All values were significantly ( P < 0.05) greater than 1. Generally, response factors for gas-chromatographic analysis using FID have been calculated on the theory that the CD of FAMEs is 1 per ester group. However, this theory could not be confirmed experimentally for short-chain FAMEs of less than 8 carbons as CDs of around 1.5 were reported for C 4 and C 6 FAMEs. The study presented here contributes an approach to this problem by confirming the validity of response factors calculated from a CD of 1.5 per ester group as well as for long-chain FAMEs and DDMEs.