100 Years of Photoionization: Ambient Analysis by APPI

This talk builds on the historical anniversary milestones of photoionization presented in the previous talks. We focus on atmospheric pressure photoionization (APPI), which is celebrating its own notable anniversaries marking 40 years since its introduction to mass spectrometry and 25 years since its commercialization and integration with liquid chromatography.

In this talk we focus on the application of APPI to ambient analysis methods of chemical detection. Ambient ionization is regarded as a relatively recent development emerging prominently with direct analysis in real time (DART) in 2005 followed concurrently by desorption electrospray ionization (DESI). Though strictly speaking ambient ionization refers to direct ionization of a collected sample on some substrate, the conceptual roots of ambient analysis go back to the 1980’s with the introduction of commercial ion mobility spectrometry (IMS) detectors incorporating various ionization methods for detection of explosives, chemical agents, narcotics, etc. using swab sampling and thermal desorption. We also consider the more recent atmospheric sample analysis probe (ASAP) desorption/ionization approach. Collectively, these techniques enable rapid, preparation-free analysis across a broad range of compounds.

We present previously demonstrated but underreported results for APPI-DART, APPI-IMS, and APPI-ASAP. In these ambient sampling contexts, APPI can replace or complement the more commonly used atmospheric pressure chemical ionization (APCI). As an adjunct to DART, APPI significantly expands compound coverage and enables the more economical and practical use of nitrogen rather than helium as the carrier gas. In IMS, most modern commercial explosives trace detectors,and related systems for chemical agent and narcotics detection, now rely on APPI-based ionization variants. Finally, we show that adapting ASAP to commercial APPI-MS systems broadens the analyte range compared with conventional APCI implementations.