Comparison of liquid chromatography/mass spectrometry interfaces for the analysis of polycyclic aromatic compounds

Abstract

Three liquid chromatography/mass spectrometry interfaces were evaluated for their suitability for the analysis of complex mixtures of polycyclic aromatic compounds (PACs). Preliminary qualitative experiments, which used a carbon black extract as test material, confirmed that the moving belt interface is mechanically awkward, is limited with respect to the mobile phase composition which it can tolerate, and is not efficient in detecting the more volatile compounds. For these reasons it was not examined further, although it performed well for larger PACs and provided electron ionization (EI) mass spectra. The particle beam (PB) interface also provides EI spectra, but detection limits are poor (low nanogram range) and calibration curves are nonlinear. Only seven of the 16 PACs targeted for quantification in a complex coal tar reference material could be detected because of the difficulty the PB interface has with the analysis of compounds with very high or very low volatility. The heated pneumatic nebulizer (HPN) interface, which uses atmospheric pressure chemical ionization, produces both molecular ions (M .+ ) and protonated molecules (MH + ) of PACs. Detection limits were in the low picogram range, and calibration curves were linear. Using the HPN interface, 17 target PACs in the coal tar reference material could be detected and quantified within satisfactory agreement with certified values when perdeuterated internal standards were employed.