Hydrazine, monomethylhydrazine, and unsymmetrical dimethylhydrazine can be detected and measured at concentrations as low as 10 parts per billion in the presence of ammonia at concentrations as high as 10 parts per million (greater than the odor threshold concentration of ammonia, approximately 5 ppm) by modified use of a portable, commercially available ion-mobility spectrometer. The modification consists in the substitution of 5-nonanone for acetone as the ion-forming compound in the drift or source region of the ion-mobility spectrometer. Previously, when acetone was used and ammonia was present in the sampled atmosphere even at ppm levels, chemical reactions between the ammonia and the acetone formed ion adducts that had mobilities comparable to those of monomethylhydrazine and that, consequently, interfered with the detection of hydrazines.

The simplicity and sensitivity of the modified ion-mobility spectrometric assay make it very attractive for use in monitoring atmospheres in vehicles and buildings where hydrazines, which can have serious adverse effects on health even at low concentrations, are being used. The modified assay also can be used to detect ammonia at concentrations ≥5 ppm.

Experience has shown that the commercially available ion-mobility spectrometer remains at top performance for 2 to 3 months, and modifications of its design may extend the performance lifetime to 12 months or more. Safety is not a factor as long as the integrity of the analyzer is maintained, and the nonanone vapor is not considered toxic at the low levels that one might expect to be vented to the atmosphere from the ion-mobility spectrometer.

Heretofore, the source of vapor has been clay adsorbent coated with nonanone, but other sources might also be used. The required concentrations of vapor are in excess of 100 parts per billion; exact values are expected to be established experimentally.

This work was done by Gary A. Eiceman of New Mexico State University, Thomas F. Limero of KRUG Life Sciences, Inc., and John L. Brokenshire of Graseby Ionics, Ltd., for Johnson Space Center. MSC21966


NASA Tech Briefs Magazine

This article first appeared in the November, 1999 issue of NASA Tech Briefs Magazine.

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