The Selected Ion Flow Tube Method for Workplace Analyses of Trace Gases in Air and Breath: Its Scope, Validation, and Applications

Abstract

We report the results of experiments that have validated our novel selected ion flow tube (SIFT) method as a rapid, real-time determination of the concentrations of trace organic vapors in air. This flow tube method relies on the soft ionization of the trace gases (to the exclusion of the major atmospheric gases) with an appropriate precursor ion species; in all these validation experiments H₃O⁺ ions were used. Standard atmospheres were created in air of several organic vapors, including ethanol, acetone, benzene, and toluene, over the concentration range from 10 ppb to 30 ppm using both the syringe dilution and the permeation tube methods, and the concentrations were measured directly using our flow tube method. Good agreement is observed between the generated concentrations as derived by these standard methods and those measured by our flow tube method, with the regression coefficients ranging from 0.91 to 1.13, the measured values being on average about 10 percent higher than the syringe-generated concentrations and about 4 percent lower than those generated by the permeation tubes. We therefore conclude that the SIFT method is a reliable, rapid method for the simultaneous determination of concentrations of several trace gases in air in real time. This technique can now be used with confidence for biological monitoring in health and safety practice, as is well demonstrated by two simple examples of breath analysis.