Quantification of small gas amounts with an ion trap mass spectrometer

Abstract

Accurate quantification of the composition in small amounts of gas is a challenging task, since there are a limited number of analytical methods having a highly sensitive and fast response. A recently introduced ion trap mass spectrometer (ITMS) was preliminarily studied as a candidate for routine quantitative analysis of small gas amounts detected as gas bursts. The ITMS was calibrated by an innovative in situ procedure using three pure gases: nitrogen, argon and hydrogen. Total pressure versus flow rate dependence was determined over three orders of magnitude, while the gas fraction pattern was simultaneously recorded by the ITMS. The obtained specific gas sensitivities of the ion gauge and pertaining ITMS fraction patterns were applied for quantification of synthetic binary gas mixtures with a composition ratio equal to 1:1, ranging from 3.17×10−3mbarL to 6.7×10−5mbarL. The error in quantification was substantially higher than for pure gases and depended on the amount and gas type. Argon was noticeably overestimated, while hydrogen was highly underestimated. At smallest gas amounts, the disproportion was as high as 1:0.36. The origin of error for low mass ions seems to be related to the ITMS's intrinsic principle of ion generation, separation and detection.