Determination of liquid chromatography/flame ionization detection response factors for N-heterocycles, carboxylic acids, halogenated compounds, and others

Many gas chromatography-flame ionization detection (GC/FID) studies are dealing with response behavior of analytes such as alcohols and alkanes. Studies in the field of liquid chromatography (LC)/FID mainly focused on volatile analytes. In contrast, studies on LC/FID by conveyor type interface covered high molecular weight non-volatile biopolymers, whereby no response factors were calculated. With this study, we fill the gap and present response factors of volatile and non-volatile analytes by LC/FID in terms of flow injection (FIA) measurements of the single compounds without an analytical separation by an LC column. In the present study, 56 different compounds such as carboxylic acids, N-heterocycles, halogenated acids, pharmaceuticals, and other compounds were investigated. In some cases, the obtained response factor data confirmed aspects known from GC/FID studies. But this study also disproves several assumptions done in previous response studies as well as the prediction models based upon the experimental data and literature. Especially the response factors and effective carbon number (ECN) values of structural isomers such as pyrazine, pyridazine, and pyrimidine are assumed to be equal in current response prediction models. Contradictory to these assumptions, the experimental response factors and ECN values of, e.g., the structural isomers pyrazine (RFExp = 0.59; ECNExp = 3.66), pyridazine (RFExp = 0.66; ECNExp = 4.1), and pyrimidine (RFExp = 0.63; ECNExp = 3.93) reveal different experimental response factors and ECN than proposed by response factor prediction models (RFExp = 0.64; ECNExp = 4). Graphical abstract Graphical abstract.