Odorant Detection by On-line Chemical Ionization Mass Spectrometry

The nasal olfactory receptors allow us, as human beings, to detect and perceive odors almost instantaneously upon exposure and over a broad range of concentrations down to ultratrace levels. Translating this rapid and sensitive detection of odorant molecules to the analytical laboratory is a challenging, nontrivial endeavor that remains unachieved to date. On-line mass spectrometry based on chemical ionization (CIMS) comprises sophisticated analytical techniques that meet several of the key requirements in odorant detection, namely fast response times and direct analyses, trace level limits of detection, and a high sensitivity to a suite of odors or, more specifically, odorants. This chapter discusses on-line CIMS and its application in odorant detection in selected fields. The prominent CIMS techniques of selected ion flow tube mass spectrometry (SIFT -MS ), proton transfer reaction MS (PTR -MS ) and atmospheric pressure chemical ionization MS (APCI-MS) are considered, commencing with a brief introduction to their historical developments and a discussion of their operational features and suitability for odorant detection, followed by a review of their widespread applications in odorant measurements in diverse fields of study.