Desorption Atmospheric Pressure Photoionization

TLDR

Desorption atmospheric pressure photoionization (DAPPI) is introduced as an ambient ionization method enabling rapid surface analysis of compounds across a range of polarities. DAPPI employs a heated nebulizer microchip to vaporize solvent (e.g., toluene) and direct a heated jet onto sample spots for desorption, while a 10‑eV photon lamp ionizes the released analytes before they enter the mass spectrometer, and its performance was benchmarked against DESI. DAPPI achieved limits of detection between 56 and 670 fmol, successfully analyzed pharmaceuticals directly from tablet surfaces, and proved equally or more sensitive than DESI, particularly for less polar analytes.

Abstract

An ambient ionization technique for mass spectrometry, desorption atmospheric pressure photoionization (DAPPI), is presented, and its application to the rapid analysis of compounds of various polarities on surfaces is demonstrated. The DAPPI technique relies on a heated nebulizer microchip delivering a heated jet of vaporized solvent, e.g., toluene, and a photoionization lamp emitting 10-eV photons. The solvent jet is directed toward sample spots on a surface, causing the desorption of analytes from the surface. The photons emitted by the lamp ionize the analytes, which are then directed into the mass spectrometer. The limits of detection obtained with DAPPI were in the range of 56−670 fmol. Also, the direct analysis of pharmaceuticals from a tablet surface was successfully demonstrated. A comparison of the performance of DAPPI with that of the popular desorption electrospray ionization method was done with four standard compounds. DAPPI was shown to be equally or more sensitive especially in the case of less polar analytes.