Analysis of quaternary ammonium compounds by pyrolysis gas chromatography

Quaternary ammonium halides (Quats) are antimicrobial compounds that are used as disinfectants and sanitizers. Promotion of their use as clinical disinfectants on hard surfaces has necessitated a method for the determination of their chemical composition. Not only is the quantity of halogen and nitrogen present in each needed, but also the length of the carbon chains attached to nitrogen. Gas Chromatography (GC) is a viable technique for separating and detecting these complex mixtures. This method has been used for the separation and identification of commercial quat disinfectants with highly complex composition containing many quaternary ammonium halides with long carbon chains. Quats are stable molecules with an estimated evaporation rate much slower than ethyl ether. They are ionic, non volatile, and they will not pass through the GC. If the injector port of the GC is held at high temperatures (250 deg. C), the long chain quaternary ammonium halide will undergo a Hofmann elimination yielding a tertiary amine. The resulting tertiary amine can then be separated by the GC. Since the Hofmann elimination can give more than one product, pure quatenary ammonium compounds were injected into the GC and the resulting products were measured. The results of these experiments were then used to determine which quats were present in the commercial preparations. Under these conditions, chromatograms with narrow and sharp peaks were obtained. Gas Chromatography coupled to mass spectroscopy (GC/MS) was used to confirm the structures of the tertiary amines produced by the Hofmann elimination. Quat standards were injected into the hot injection port of the GC/MS and the mass spectrum of the peaks eluting from the GC were measured. This method gave reproducible spectra using the same chromatographic conditions.