PNNL

Abstract

We present here a description of an LED photoemmision ionization source for use in mass spectrometry for detection of volatile organic vapors and organic residues. This technique relies upon the generation of photoelectrons from a low-work function metal via low-energy UV light (280nm) generated by a single LED at atmospheric pressure and room temperature. These low-energy photoelectrons result in both direct electron capture by the analyte or chemical ionization via O2-. Ion generation occurs without use of high electric fields such as corona discharge or ESI. Further, this source was found to be effective for measuring both organic vapors and organic residues off surfaces. Experimental evidence suggests the dominant ionization pathway involves: first, photoemission off a conductive surface; second, electron capture by oxygen (or an electrophilic analyte), followed thirdly by atmospheric chemical ionization of an analyte. Several classes of organic vapors were analyzed and found to be effectively detected including alcohols, acids, heterocyclic aromatics and halo-organic solvents. Analysis of dry organic residues of 100ng of TNT on various surfaces is measured, including glass, various metal foils and a stainless steel mesh.