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Use of Calibration Gas in a Helium Matrix for Calibrating APIMS Used to Analyze Impurities in any Gas

IP.com Disclosure Number: IPCOM000019382D
Publication Date: 2003-Sep-12
Document File: 2 page(s) / 105K

Publishing Venue

The IP.com Prior Art Database

Abstract

The normal practice in the calibration of an atmospheric pressure ionization mass spectrometer (APIMS) is to use a calibration gas mixture in the same gas as the gas to be analyzed. Typically an APIMS is used to determine impurities in bulk N2, Ar, H2 and He. Thus to analyze the four bulk gases four calibration standards one each in N2, Ar, H2 and He are required. In addition if one wants to estimate the maximum concentration possible of CO and N2 in Ar, H2 and He, single component standards of either N2 or CO in Ar, H2 and He are also needed. Thus a total of at least 7 calibration standards are required. In order to accurately quantify the APIMS results the calibration standards have to be analyzed against primary standards.

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Use of Calibration Gas in a Helium Matrix for Calibrating APIMS Used to Analyze Impurities in any Gas

The normal practice in the calibration of an atmospheric pressure ionization mass spectrometer (APIMS) is to use a calibration gas mixture in the same gas as the gas to be analyzed. Typically an APIMS is used to determine impurities in bulk N2, Ar, H2 and He. Thus to analyze the four bulk gases four calibration standards one each in N2, Ar, H2 and He are required. In addition if one wants to estimate the maximum concentration possible of CO and N2 in Ar, H2 and He, single component standards of either N2 or CO in Ar, H2 and He are also needed. Thus a total of at least 7 calibration standards are required. In order to accurately quantify the APIMS results the calibration standards have to be analyzed against primary standards.

Helium has the highest ionization potential known, so the presence of a small quantity of helium in the ionization source of an APIMS, which is being used to analyze any gas, will not quench the ion-molecule reactions between the ions of the gas being analyzed and the atoms/molecules of the impurities being detected. This fact can be used to our advantage by using a calibration standard prepared in a helium. At high dilution ratios ( from 1000:1 to 10000:1) the presence of a small amount of helium will not influence the charge transfer to the impurities. As the dilution ratio is decreased the helium will start to influence the charge transfer till a point is reached when the helium will totally dominate the charge transfer rates thereby giving response factors which will be valid only in helium. By the appropriate choice of impurity concentrations in the calibration gas we can restrict ourselves to high dilution ratios so that the presence of small amount of helium will not produce any undesired results.

Calibration experiments were performed using calibration standards in He and calibration standards in N2, to calibrated the APIMS use...