Ion mobility spectrometry of hydrazine, monomethylhydrazine, and ammonia in air with 5-nonanone reagent gas

Abstract

Hydrazine (HZ) and monomethylhydrazine (MMH) in air were monitored continuously using a hand-held ion mobility spectrometer equipped with membrane inlet, 63Ni ion source, acetone reagent gas, and ambient temperature drift tube. Response characteristics included detection limit, 6 ppb; linear range, 10-600 ppb; saturated response, >2 ppm; and stable response after 15-30 min. Ammonia interfered in hydrazines detection through a product ion with the same drift time as that for MMH and HZ. Acetone reagent gas was replaced with 5-nonanone to alter drift times of product ions and separate ammonia from MMH and HZ. Patterns in mobility spectra, ion identifications from mass spectra, and fragmentation cross-sections from collisional-induced dissociations suggest that drift times are governed by ion-cluster equilibria in the drift region of the mobility spectrometer. Practical aspects including calibration, stability, and reproducibility are reported from the use of a hand-held mobility spectrometer on the space shuttle Atlantis during mission STS-37.

Mobility resolution and mass analysis of ions from ammonia and hydrazine complexes with ketones formed in air at ambient pressure

“…The reason for the success with a reagent gas was not understood in reference [4] where the observed order of the drift times of the complexes, ammonia Ͼ hydrazine Ͼ monomethylhydrazine was inverted from the size or mass of the neutral molecules, M. In this study, the order of drift times for 5-nonanone complexes as shown previously was confirmed as: ammonia Ͼ hydrazine Ͼ monomethylhydrazine Ͼ unsymmetrical dimethylhydrazine. Experiments with a simple drift tube interfaced to a mass spectrometer were used to identify the complexes and other unexpected complexes of protonated hydrazones and protonated azines.…”

“…In contrast, addition of ketone vapor in at the detector (FigureÅ 1,Å bottomÅ frame)Å providedÅ aÅ uniformÅ gasÅ atmosphere for ion drift, favoring equilibria as shown in eq 1. Concentrations of reagent gas were referenced to a prior studyÅ [4]Å andÅ judgedÅ byÅ observationÅ andÅ analysisÅ ofÅ the mobility spectra.…”

“…When 5-nonanone was used as a reagent gas, instead of acetone, the reactant ions generated were the protonated molecule C 9 H 18 OH ϩ and the proton-bound dimer (C 9 H 18 O) 2 H ϩ . Significantly, the ion-molecule complexes formed by these ions with ammonia and the hydrazines had even longer drift times than those obtained with acetone, and the resolution between peaks in mobility spectra was sufficient for monitoring vapor levels on board the Space Shuttle [4]. Ion drift times and resolution in spectra were shown to be dependent upon the concentration of ketone in the drift gas changing rapidly until 100 ppm v of ketone in the entire supporting atmosphere of the drift tube.…”

“…Traditional methods of colorimetry and amperometry [1,2] are limited in convenience of use and in specificity by chemical or physical interferences from ammonia, moisture, and other vapors. A selective, sensitive, and fast method for the quantitative determination of hydrazines has been demonstrated [3,4] through the gas-phase ionization technique of ion mobility spectrometry (IMS). Such favorable performance can be ascribed to the high proton affinities of hydrazines as found also in atmospheric pressure chemical ionization mass spectrometry (APCI-MS).…”

“…Extension of this concept to a hand-held mobility spectrometer, with a drift tube at ambient temperature, lead to unacceptable resolution of the protonated molecules through formation of hydrated cluster ions without distinctive drift times [4]. Analytically viable separation of ions was sought with acetone as a reagent gas to generate reactant ions (C 3 H 6 O) n H ϩ that would then form ion-molecule complexes containing ammonia or a hydrazine, proton-bound with one or more acetone molecules [4]. Though the resulting ion-molecule com-plexes had drift times larger than those for hydrated protonated molecules, the improved stability in drift behavior and peak separations in spectra were insufficient for specific and quantitative determinations.…”