A Simple Atmospheric Pressure Ionization Source Coupled to a Timeof-Flight Mass Spectrometer for Breath Analysis

10. Dresdner Sensor-Symposium 2011
2011-12-05 - 2011-12-07
Sensoren für die Medizin I
J. Langejuergen, P. Cochems, S. Zimmermann - Hannover
87 - 90


The analysis of exhaled breath accesses a variety of new diagnostic methods. However, this requires new analytical tools combining sufficient separation power (mass resolution) with ppt-level detection limits. A time-of-flight mass spectrometer (ToF-MS) is a suitable choice to analyze an entire mass spectrum of gaseous samples within a comparatively short sample time (0.5 s) at high mass resolution. However, the required detection limits can only be obtained by using atmospheric pressure ionization known from ion mobility spectrometry. Here we present a simple atmospheric pressure ionization source based on electron impact ionization coupled to a Bruker micrOTOF II mass spectrometer giving excellent mass resolution combined with ultra-high sensitivity. We achieve detection limits, e.g. for Acetone, in the lower ppt-range at 0.5 s integration time. The mass resolution is approx. 3000 at 60 u. However, one major drawback of this method is that competing proton transfer processes in the ionization chamber make quantitative analysis difficult. Thus, we use a gas chromatograph for pre-separation. As an example, here we analyze end-tidal human breath sampled on Tenax TA adsorption tubes using our CO2-triggered breath sampling unit.
Furthermore, a thermal desorption system (TDS) coupled to a cold injection system (CIS) for sample injection into the gas chromatograph (GC) is used. Two-dimensional heat-maps of the abundance of ion masses versus the GC retention time are shown for inhaled (laboratory air) and exhaled human breath. Several substances are detected within the breathing gas sample only. An identification of these substances as well as a better control of the ionization process are subject to future investigations. Here we just present our tool for breath analysis.