Analysis of hydrocarbons in a hydrogen atmosphere by gas chromatography with flame ionization

Abstract

The ionization response of hydrocarbons In a hydrogen-atmosphere flame was compared to that of a normal flame ionization detector used in gas chromatography. Absolute response in the hydrogen-atmosphere flame lonizatlon detector (HAFID) was found to be two orders of magnitude less than that of the normal FID. This reduced response is attributed both to oxidation of hydrocarbons in the precombustion zone of the flame and to differences In collecting electrode positions in the two detectors. Relative responses for hydrocarbons in the two flames were found to be similar. Both systems responded to hydrocarbons in a manner proportional to the number of carbon atoms in a test compound. These results do not support the postulate that H-atom cracking in the precombustion zone of a flame Is the initial mechanism for the origin of single carbon units in the FID. Relative response similarities did not extend to aromatic or hetero compounds.Since the introduction of the flame ionization detector (FID) by McWilliams and Dewar in 1958 (1, Z), flame ionization has been the major detection method for hydrocarbons in gas chromatography (GC). The FID enjoys a widespread popularity for a variety of reasons such as durability, low cost, high sensitivity, and a predictable relative response. For hydrocarbons, response is proportional to the number of unoxidized carbon atoms in a molecule (3-9).T h e origin of this proportional carbon response is one of the most interesting facets of the FID mechanism. Though it is generally accepted that preionization reactions which reduce hydrocarbons to single carbon units in the precombustion zone of the flame are the origin of this response, it is not a t all clear what reactions these might be. Sternberg et al. (5) suggested that single carbon units are produced near the outer boundary of the oxygen free precombustion zone by partial pyrolysis followed by Rice-Herzfeld cracking processes (10) that are initiated by back-diffusion of hydrogen atoms from the main reaction zone. On the other hand, Peeters, Lambert, Hertoghe, and Van Tiggelen (11) have proposed oxidative degradation while, more recently, Blades (12) has argued for H-atom cracking.Blades claimed evidence for H-atom cracking based on a comparison of four flames in which reaction gases were introduced in a variety of ways: an H2-in-air diffusion flame with the hydrocarbons in air, an 0,-N2 diffusion flame in H 2 with hydrocarbons in 02-N2, a premixed H2-02-N2-hydrocarbon flame and a normal FID with hydrocarbons in H2. Only when hydrocarbons were placed in a hydrogen-rich precombustion environment did he observe response proportional to the number of carbon atoms.T h e hydrogen atmosphere flame ionization detector (HAFID), which has been developed as a GC selective detector for organometallics and silicon containing compounds (13)(14)(15)(16), offers a convenient method by which to explore further the effects on ionization when hydrocarbons are introduced into a flame from an oxygen-rich environment. This paper serves to investigate ...

CH and C2 Measurements Imply a Radical Pool within a Pool in Acetylene Flames

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Production of positive ions during the catalytic oxidation of organic vapors on hot platinum

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Comparison of metal-sensitive flame ionization and carbon-sensitive flame ionization detectors for the gas chromatographic determination of organotins

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