Method and apparatus for improving the specificity of an ion mobility spectrometer utillizing sulfur dioxide dopant chemistry

Claim 2

An improved method for operating an ion mobility spectrometer using air as a carrier gas and as a drift gas, said spectrometer comprising an analyzer cell having an inlet region, a reaction region, an ionization source in said reaction region, a shutter grid, a drift region, an ion current detector for detecting ions transiting said cell drift region, and means for measuring the transit times through said cell drift region of ions generated in said cell reaction region and released into said cell drift region through said shutter grid, the method comprising the steps of: applying a drift gas stream of air to said cell drift region; mixing sulfur dioxide with a carrier gas stream of air to create a doped carrier gas stream; introducing a test sample of gas into said analyzer cell inlet region; applying said carrier gas stream to said cell inlet region to carry said test sample into said cell reaction region; and measuring an ion current at said ion current detector at a time corresponding to the transit time through said cell drift region of ions generated by said test sample in said cell reaction region; whereby said sulfur dioxide dopant causes ions generated by said carrier gas stream in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 3

The improved method according to claim 1, whereby said step of mixing sulfur dioxide suppresses a componant of said measured ion current attributable to ions generated by test sample acid gasses with low charge affinities, said measured ion current being attributable mainly to ions generated by test sample acid gasses with high charge affinities.

Claim 4

The improved method of claim 1, wherein: said test sample comprises hydrogen fluoride.

Claim 5

The improved method as claimed in claim 1, wherein: said test sample comprises sulfur dioxide.

Claim 6

The improved method as claimed in claim 1, wherein: said test sample comprises carbonyl sulfide.

Claim 7

The improved method of claim 1, wherein: said step of mixing sulfur dioxide comprises mixing sulfur dioxide dopant in said carrier stream of air at a concentration of approximately 1 part per million.

Claim 8

The improved method of claim 1 wherein: said step of mixing sulfur dioxide with said carrier gas stream of air is accomplished by using a sulfur dioxide permeation tube immersed in said carrier gas stream, whereby said carrier gas mixes with sulfur dioxide permeating through said tube.

Claim 9

The improved method of claim 1, wherein said ion mobility spectrometer is operated in a negative ion mode.

Claim 10

An improved method for operating an ion mobility spectrometer using air as a carrier gas and as a drift gas, said spectrometer comprising an analyzer cell having an inlet region, a reaction region, an ionization source in said reaction region, a shutter grid, a drift region, an ion current detector for detecting ions transiting said cell drift region, and means for measuring the transit times through said cell drift region of ions generated in said cell reaction region and released into said cell drift region through said shutter grid, the method comprising: introducing a test sample of gas into said analyzer cell inlet region; applying a carrier gas stream to said cell inlet region to carry said test sample into said cell reaction region; applying a drift gas stream of air to said cell drift region; mixing sulfur dioxide with said drift gas stream of air to create a doped drift gas stream for carrying product ions generated by said test sample in said cell reaction region into said cell drift region; and measuring a product ion current at said ion current detector at a time corresponding to the transit time through said cell drift region of said product ions; whereby said sulfur dioxide dopant causes ions generated by said drift gas in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 11

An improved method for operating an ion mobility spectrometer using air as a carrier gas and as a drift gas, said spectrometer comprising an analyzer cell having an inlet region, a reaction region, an ionization source in said reaction region, a shutter grid, a drift region, an ion current detector for detecting ions transiting said cell drift region, and means for measuring the transit times through said cell drift region of ions generated in said cell reaction region and released into said cell drift region through said shutter grid, the method comprising: introducing a test sample of gas into said analyzer cell inlet region; applying a carrier gas stream to said cell inlet region to carry said test sample into said cell reaction region; applying a drift gas stream of air to said cell drift region; mixing sulfur dioxide with said drift gas stream of air to create a doped drift gas stream for carrying product ions generated by said test sample in said cell reaction region into said cell drift region; and measuring a product ion current at said ion current detector at a time corresponding to the transit time through said cell drift region of said product ions; whereby said sulfur dioxide dopant causes ions generated by said drift gas in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 12

The improved method according to claim 9, whereby said step of mixing sulfur dioxide suppresses a componant of said measured ion current attributable to ions generated by test sample acid gasses with low charge affinities, said measured ion current being attributable mainly to ions generated by test sample acid gasses with high charge affinities. ions generated by test sample acid gases with high charge affinities to have transit times through said cell drift region which are different from the transit times through said cell drift region of product ions generated by test sample acid gasses with low charge affinities.

Claim 13

The improved method as claimed in claim 9, wherein: said test sample comprises hydrogen fluoride.

Claim 14

The improved method as claimed in claim 9, wherein: said test sample comprises sulfur dioxide.

Claim 15

The improved method as claimed in claim 9, wherein: said test sample comprises carbonyl sulfide.

Claim 16

The improved method of claim 9, wherein: said step of introducing sulfur dioxide comprises introducing sulfur dioxide in said drift gas stream of air at a concentration of approximately 1 part per million.

Claim 17

The improved method of claim 9, wherein: said step of mixing sulfur dioxide with said drift gas stream of air is accomplished by using a sulfur dioxide permeation tube immersed in said drift gas stream, whereby said drift gas mixes with sulfur dioxide permeating through said tube.

Claim 18

The improved method of claim 9, further comprising the step of: mixing sulfur dioxide with said carrier gas stream of air to create a doped carrier gas stream.

Claim 19

The improved method as claimed in claim 9, wherein said ion mobility spectrometer is operated in a negative ion mode.

Claim 20

An ion mobility spectrometer for analyzing an acid gas in a test sample, comprising: an inlet region for inputting a test sample of gas; a reaction region in fluid communication with said inlet region; means for applying a carrier gas stream of air to said inlet region for carrying said test sample therefrom into said cell reaction region; doping means for introducing sulfur dioxide into said carrier gas stream of air; an ionization source in said reaction region for generating product ions from the test sample carried into the reaction region by said carrier gas; a drift region through which said product ions travel in accordance with a charge and molecular size characteristic; a shutter grid for selectively releasing said product ions from said reaction region into said drift region; an ion current detector for detecting product ions transiting said cell drift region; means for measuring a transit time through said cell drift region of product ions generated in said cell reaction region and released into said cell drift region through said shutter grid; and means for measuring an ion current detected by said cell ion current detector at a time corresponding to the drift time of ions generated from said analyte gas in said cell reaction region; whereby sulfur dioxide dopant introduced by said doping means causes ions generated by said carrier gas stream in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 21

An ion mobility spectrometer for analyzing an acid gas in a test sample, comprising: an inlet region for inputting a test sample of gas; a reaction region in fluid communication with said inlet region; means for applying a carrier gas stream of air to said inlet region for carrying said test sample therefrom into said cell reaction region; doping means for introducing sulfur dioxide into said carrier gas stream of air; an ionization source in said reaction region for generating product ions from the test sample carried into the reaction region by said carrier gas; a drift region through which said product ions travel in accordance with a charge and molecular size characteristic; a shutter grid for selectively releasing said product ions from said reaction region into said drift region; an ion current detector for detecting product ions transiting said cell drift region; means for measuring a transit time through said cell drift region of product ions generated in said cell reaction region and released into said cell drift region through said shutter grid; and means for measuring an ion current detected by said cell ion current detector at a time corresponding to the drift time of ions generated from said analyte gas in said cell reaction region; whereby sulfur dioxide dopant introduced by said doping means causes ions generated by said carrier gas stream in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 22

The ion mobility spectrometer according to claim 18, whereby said sulfur dioxide dopant suppresses a componant of said measured ion current attributable to ions generated by test sample acid gasses with low charge affinities, said measured ion current being attributable mainly to ions generated by test sample acid gasses with high charge affinities.

Claim 23

The apparatus according to claim 18, wherein said sulfur dioxide doping means comprises a gas permeable tube immersed in said carrier gas stream for allowing dopant contained therein to permeate into said carrier gas stream.

Claim 24

The apparatus according to claim 20, wherein said gas permeable tube introduces said dopant to said carrier gas at a rate of about 365 nanograms per minute.

Claim 25

The apparatus according to claim 18, wherein said inlet region is partitioned by means for preventing passage of select constituents of said test sample.

Claim 26

The apparatus according to claim 22, wherein said partition means is a gas-permeable membrane.

Claim 27

The apparatus according to claim 18, further comprising processing means for computing a quantity of an acid gas constituent in said test sample based on said ion current measured by said ion current measurement means.

Claim 28

The apparatus according to claim 24, wherein said processing means further comprises a memory for storing expected peak ion current data characteristic of said constituent acid gas in said test sample, said processing means comparing actual measured ion currents detected by said cell ion current detector to said expected peak ion current data and quantifying said constituent based on said comparison.

Claim 29

The apparatus according to claim 25, wherein said expected peak ion current data comprises a calibration curve relating said actual measured ion currents to said constituent concentration.

Claim 30

An ion mobility spectrometer for analyzing an acid gas in a test sample, the spectrometer comprising: an inlet region for introduction of said test sample of gas, said inlet region having means for allowing a limited amount of said test sample to penetrate; a reaction region in fluid communication with said inlet region; an ionization source in said reaction region for generating product ions from the test sample carried into the reaction region by said carrier gas; a drift region through which said product ions travel in accordance with a charge and molecular size characteristic; a shutter grid for selectively releasing said product ions from said reaction region into said drift cell drift region; means for applying a drift gas stream of air to said to said drift region for carrying test sample having penetrated said membrane into said cell reaction region; means for introducing sulfur dioxide dopant to said carrier gas stream of air and to said drift gas stream of air; an ion current detector for detecting product ions transiting said cell drift region; and means for measuring the transit times through said cell drift region of product ions generated in said cell reaction region and released into said cell drift region through said shutter grid; means for measuring an ion current detected by said cell ion current detector at a time corresponding to the drift time of ions generated from said analyte gas in said cell reaction region to provide an ion current value; whereby said sulfur dioxide dopant causes ions generated by said carrier gas stream and drift gas stream in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 31

An ion mobility spectrometer for analyzing an acid gas in a test sample, the spectrometer comprising: an inlet region for introduction of said test sample of gas, said inlet region having means for allowing a limited amount of said test sample to penetrate; a reaction region in fluid communication with said inlet region; an ionization source in said reaction region for generating product ions from the test sample carried into the reaction region by said carrier gas; a drift region through which said product ions travel in accordance with a charge and molecular size characteristic; a shutter grid for selectively releasing said product ions from said reaction region into said drift cell drift region; means for applying a drift gas stream of air to said to said drift region for carrying test sample having penetrated said membrane into said cell reaction region; means for introducing sulfur dioxide dopant to said carrier gas stream of air and to said drift gas stream of air; an ion current detector for detecting product ions transiting said cell drift region; and means for measuring the transit times through said cell drift region of product ions generated in said cell reaction region and released into said cell drift region through said shutter grid; means for measuring an ion current detected by said cell ion current detector at a time corresponding to the drift time of ions generated from said analyte gas in said cell reaction region to provide an ion current value; whereby said sulfur dioxide dopant causes ions generated by said carrier gas stream and drift gas stream in said cell reaction region to have transit times through said cell drift region which are different from the transit times through said cell drift region of ions generated by the test sample.

Claim 32

The ion mobility spectrometer according to claim 27, whereby said sulfur dioxide dopant suppresses a componant of said measured ion current attributable to ions generated by test sample acid gasses with low charge affinities, said measured ion current being attributable mainly to ions generated by test sample acid gasses with high charge affinities.

Claim 33

The ion mobility spectrometer according to claim 27, whereby said means for allowing a limited amount of said test sample to penetrate said inlet region further comprises a gas permeable membrane.

Claim 34

The apparatus according to claim 27, wherein said sulfur dioxide doping means comprises a gas permeable tube immersed in said drift gas stream, and a gas permeable tube immersed in said carrier gas stream, whereby dopant in said tube permeates therethrough into said drift and carrier gas streams.

Claim 35

The apparatus according to claim 30, wherein said gas permeable tube introduces said dopant to each of said drift and carrier gas streams at a rate of about 365 nanograms per minute.

Claim 36

The apparatus according to claim 27, further comprising processing means for computing a quantity of an acid gas constituent in said test sample based on said ion current measured by said ion current measurement means.

Claim 37

The apparatus according to claim 32, wherein said processing means further comprises a memory for storing expected peak ion current data characteristic of said constituent acid gas in said test sample, said processing means comparing actual measured ion currents detected by said cell ion current detector to said expected peak ion current data and quantifying said constituent based on said comparison.

Claim 38

The apparatus according to claim 33, wherein said expected peak ion current data comprises a calibration curve relating said actual measured ion currents to said constituent concentration.