Analysis of trace n-alkane in air by cryogenic-temperature programmed desorption

Abstract

Exhaled breath analysis is a promising medical monitoring method, but its practical use is currently very limited. This is due to the very low concentration of the disease marker; hence, advanced (research-level) analytical instrumentation has been typically employed. Cryogenic-temperature programmed desorption (cryo-TPD) has been developed as a simple method of breath analysis. In cryo-TPD, the disease markers are selectively concentrated by quench condensation at cryogenic temperature combined with subsequent ramped heating. The influence of the interaction between the markers on the thermal desorption (gas mixing effect) is crucial for the practical use of cryo-TPD for breath analysis. In the present study, the authors found that the gas mixing effect causes almost no change in thermal desorption of n-alkanes (CNH2N+2, 2 ≦ N ≦ 12) in air. Consequently, trace alkanes were successfully and selectively concentrated and subsequently quantified in the concentration range of 1 × 10−9 (1 ppbv) to 1 × 10−4 (100 ppmv) volume fractions. The lowest limit of detection of n-hexane, which was estimated to be less than 0.5 ppbv for a condensation duration of 100 s, is expected to be substantially improved by the prolonged condensation.