The detection of hydrazine and related materials by ion mobility spectrometry.

A technique known as ion mobility spectrometry (IMS), which has been under development for about thirty years, has been shown to be capable of detecting hydrazines at low concentrations but with interference from ammonia. Ammonia is usually present in hydrazine environments, as a breakdown product or a by-product of the human metabolism. This project was undertaken to investigate mechanical and chemical parameters for improved detection of these hydrazines in the presence of ammonia, and for the detection of nitrogen dioxide, by IMS. The subject areas investigated were compatibility of detector cell construction materials with the analytes, detector temperature, comparison of membrane versus direct inlet systems under their optimum conditions, pneumatics configurations for the spectrometer, and the investigation into the effects of different ion molecule chemistry regimes for the improvement of selectivity, sensitivity, and response and recovery times. The optimum spectrometer operating conditions, for the detection of hydrazine, methylhydrazine, and 1,1-dimethylhydrazine in the presence of ammonia, and for the detection of nitrogen dioxide, were incorporated into a hand portable instrument (linked to a computer) capable of near real-time detection. Ammonia is still an interferent in the ion mobility spectrometry detection of the parent hydrazine. The use of ketones as dopant chemicals has been shown to be effective in the ion mobility spectrometric determination of the hydrazines. However, the mobility of the ion-molecule clusters formed from these hydrazines are in the reverse order to that expected. In order to gain insight to the ion-molecule chemistry of the hydrazines/ketones systems molecular modelling and IMS coupled with tandem mass spectrometry studies were undertaken to investigate ion cluster formations of the hydrazines with an homologous series of symmetrical ketones. A fluorinated ketone was also studied by IMS-MS-MS to determine the effect of electron withdrawing groups upon ion cluster formation. The ion-molecule clusters formed were shown to be concentration dependent, with gas phase reaction recorded between the dopants and analytes at low ketone concentration.