Development of a next-generation field-free atmospheric pressure photoionization source for liquid chromatography/mass spectrometry.

Rationale: Atmospheric pressure photoionization (APPI) is considered a candidate ionization method suitable for a broad range of liquid chromatography/mass spectrometry (LC/MS) applications. Questions remain, however, regarding the ultimate potential of the technique. We propose that sensitivity and thus detection limits may be restricted by geometric source design, limiting widespread acceptance of the technique.

Methods: The relative performance of two geometrically distinct APPI source configurations was evaluated through comprehensive performance comparison upon a single MS platform. To facilitate a fair comparison, a prototype orthogonal geometry, field-free APPI source was developed and tested against two currently commercially available open-geometry APPI sources. The prototype device was engineered based upon the geometry and functionality of first-generation, co-axial field-free APPI sources.

Results: Initial characterization experiments were performed by flow injection analysis using a range of analyte standards exhibiting a variety of chemical properties. A standard panel of 16 polycyclic aromatic hydrocarbons (PAHs) identified as priority pollutants by the EPA was also analyzed, demonstrating relative performance using an LC/MS workflow. The prototype field-free APPI source demonstrated the potential for order-of-magnitude performance enhancement over open-geometry sources that lack a confined field-free reaction region.

Conclusions: An APPI source configuration that includes an extended field-free reaction region was demonstrated to have the potential to provide enhanced sensitivity relative to commercially available open-geometry source designs. Improved performance will no doubt lead to increased acceptance and widespread application of the technique.