Ion mobility spectrometer system with improved specificity

A method for increasing the specificity of an ion mobility spectrometer to the constituents of a sample characterized by the steps of:

• continuously mixing with a carrier gas, at least one reagent having a higher proton affinity, electron affinity, or acidity than the constituents of the sample to be detected and which does not cluster with water to form a reagent/carrier mixture;
• combining said reagent/carrier mixture with a sample gas to form a reagent/carrier/sample mixture;
• and
• ionizing said reagent/carrier/sample mixture to form stable ions of said reagent, said stable ions reacting with said sample to produce ions characteristic of the constituents of the sample.

An ion mobility spectrometer system comprising:

• an ion mobility spectrometer having a reaction chamber, a contiguous drift chamber, an injection grid separating said reaction and drift chambers, ionization means disposed in said reaction chamber, a collector electrode disposed in said drift chamber opposite said injection electrode and means for generating a electrostatic field gradient across said contiguous reactant and drift chambers;
• pump means for supply a continuous flow of a carrier gas though said reaction and drift chambers
• means for injecting a sample gas having at least one constituent to be detected into the carrier gas flow supplied to said reaction chamber;
• reagent source means for injecting at least one reagent into the flow of carrier gas supplied to said reaction chamber, said reagent having a proton affinity, electron affinity, or acidity greater than water an less the constituents of the sample gas to be detected and which does not cluster with water;
• means for periodically generating an injection signal biasing said injection grid for a short period of time to transmit a portion of the ions generated in said reaction chamber to said drift chamber;
• amplifier means for generating an ion signal indicative of the number of ions collected by the collector electrode;
• and
• an electronic processing unit responsive to the time differential between said injection signal and said ion signals for generating a signature indicative of the characteristics of the sample gas.

In an ion mobility spectrometer wherein a sample having at least one constituent to be detected and a carrier gas are injected into the reaction chamber of the ion mobility spectrometer and wherein the sample contains contaminants including water which reduce the specificity of the ion mobility spectrometer, an improvement for increasing the specificity of the ion mobility spectrometer characterized by:

• reagent source means for mixing with the carrier/gas at least one reagent having a proton affinity greater than water and less than the proton affinity of the constituents of the sample to be detected and which does not cluster with water to produce a reagent/carrier mixture;
• a permeable mebrane selectively permeable to the at least one constituent of the sample to be detected;
• means for directing a flow of the sample onto one surface of said permeable membrane;
• means for directing a flow of said reagent/carrier mixture onto the opposite surface of said permeable membrane to mix said reagent and carrier gas with the constituents of the sample permeated therethrough;
• and
• means for conducting said reagent/carrier mixture and the permeated constituents of the sample into the reaction chamber of said ion mobility spectrometer.