Temperature Programmed Desorption of Quench-condensed Krypton and Acetone in Air; Selective Concentration of Ultra-trace Gas Components

Abstract

Selective concentration of ultra-trace components in air-like gases has an important application in analyzing volatile organic compounds in the gas. In the present study, we examined quench-condensation of the sample gas on a ZnO substrate below 50 K followed by temperature programmed desorption (TPD) (low temperature TPD) as a selective gas concentration technique. We studied two specific gases in the normal air; krypton as an inert gas and acetone as a reactive gas. We evaluated the relationship between the operating condition of low temperature TPD and the lowest detection limit. In the case of krypton, we observed the selective concentration by exposing at 6 K followed by thermal desorption at about 60 K. On the other hand, no selectivity appeared for acetone although trace acetone was successfully concentrated. This is likely due to the solvent effect by a major component in the air, which is suggested to be water. We suggest that pre-condensation to remove the water component may improve the selectivity in the trace acetone analysis by low temperature TPD.

Selective Concentration of Ultra-trace Acetone in the Air by Cryogenic Temperature Programmed Desorption (cryo-TPD)

“…The schematic illustration of our cryo-TPD has been published elsewhere. 7 The electron multiplier option of QMS was not used in the present study. Thus, the ion current of QMS was measured by merely a conventional faraday cup.…”

“…The removal of the water component by the pre-condensation technique has been examined in our previous study. 7 Briefly, the pre-condensation for concentrating the water component followed by cryo-TPD improves the trace analytical ability.…”

“…The prolonged exposure reduces the error in the estimation of the TPD peak, thus the y-axis error. 7 On the other hand, more precise control of the acetone partial pressure is needed to reduce the error along the x-axis. Thus, a more accurate gas mixing technique is needed to evaluate cryo-TPD in the range below the ppbv level.…”

“…7 The technique is essentially the same with TPD or thermal desorption spectroscopy, which have been widely used in solid surface analysis. [8][9][10] However, to the best of our knowledge, cryo-TPD has not been seriously examined from the point of view of the selective gas concentration for (ultra-) trace gas analysis.…”

“…4,6,[22][23][24][25][26] In our previous study, we have preliminarily shown that cryo-TPD is useful for the selective acetone concentration in the air, where the acetone concentration was in the range of the ppmv level. 7 In the present study, we have further investigated the performance of cryo-TPD for quantitative analysis of acetone at the ppbv level. This is motivated by the possible future application of cryo-TPD to exhaled breath analysis for medical monitoring.…”