Miniature ThermoelectricCooler for Long-Term StableDehydration for On-Site Breath Analysis by Direct Inlet PhotoionizationIon Mobility Spectrometry and Mass Spectrometry

Rapid and highly frequent measurements of exhaled breath hold significant value for disease diagnosis and exposure assessments. Direct inlet mass spectrometry and ion mobility spectrometry demonstrate great potential for on-site breath analysis, but their accuracy and sensitivity are notably affected by the high humidity in the breath samples. A miniature and continuous dehydration device based on dual-switching thermoelectric cold traps has been developed to efficiently reduce the humidity of breath gas from saturation to relative humidity of 4.3%, and a subcooling compensation method was adopted to eliminate the humidity fluctuations when switching the two cold traps to remove the condensed water in the trap, which could achieve a stable outlet humidity with RSD of 8.2% regardless of inlet humidity variations. The performance and profits of the miniature dehydration device for on-site analysis of breath samples have been tested by coupling with direct inlet photoionization ion mobility spectrometry and time-of-flight mass spectrometry. Trace breath acetone could be directly measured, and its concentration profiles over an 8 h period in fasting volunteers could be continuously monitored every 30 s. Furthermore, the <i>m</i>/<i>z</i> peaks from chlorinated hydrocarbons in exhaled breath samples were clearly identified after passing the dehydration device, which can be used for an occupational health assessment of the widely used halocarbon solvents.