Electrospray and Atmospheric Pressure Chemical Ionisation of Aromatic Compounds in Dichloromethane Solvent

Abstract

Atmospheric pressure chemical ionisation (APCI) of chlorinated benzene derivatives was studied to develop a mass spectrometry technique for qualitative and quantitative determination of their aerobic and anaerobic microbial degradation products. Using conventional reversed phase-high performance liquid chromatography (RP-HPLC) eluents, such as methanol, water or acetonitrile, non-polar aromatic compounds showed very low response factors both in electrospray (ES) and in APCI either in positive or negative ion mode. Use of dichloromethane solvent in positive ion APCI showed high sensitivity both for polar and for apolar aromatics. Oxygen containing compounds gave [M + H]⁺ ions while ionisation of aromatic hydrocarbons and their chlorinated derivatives was found to be a complex process, generating mainly [M + 13]⁺ ions. Detailed investigations showed that ionisation proceeds by the addition of CH₂Cl⁺ followed by HCl elimination.