Response of flame ionization detectors to different homologous series

Hydrogen flame-ionization detectors (FIDs) are the most widely used type of detector in gas chromatography The FID signal is proportional to the number of carbon atoms in a hydrocarbon molecule; the presence of heteroatoms usually reduces the signal. If the extent of the signal-reducing effect of heteroatoms were known, it would be possible to measure compounds which are not available as pure standards, or cannot be prepared, or their preparation is very expensive. The sensitivity of a detector to on organic molecule containing heteroatoms is referred to normal hydrocarbons by means of the effective carbon-atom number (ECN) value. By use of the values of increments in ECN for heteroatoms and functional groups, the ECN can be calculated far any organic molecule. For this, exact values of the ECN increments are needed, and the effects of different factors on the increments must be known. In this study a wide range of homologues of normal paraffins, alcohols, amines, and esters was investigated, with emphasis on differences between the behaviour of lower and higher homologues. Studies were extended to the ECN values of ketones, and aromatic and halogenated compounds. For all types of compound investigated the difference between the actual carbon number and the calculated effective carbon number (dECN) was compared with literature data, and an attempt was made to interpret the differences.