Phenyl-modified reversed-phase liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry: A universal method for the analysis of partially oxidized aromatic hydrocarbons

A new liquid chromatographic method for the efficient separation of aromati c compounds having a wide range of sizes, molecular structures, and polarit ies has been developed. Based on a phenyl-modified silica reversed stationa ry phase and a methanol-water solvent gradient, it allows the separation of mono- and polycyclic aromatic hydrocarbons (PAHs) having up to five conden sed aromatic rings and partially oxidized derivatives within a single chrom atographic run of 40-min duration. The applicability of the method is demon strated using 81 reference substances (PAHs, phenols, quinones, acids, lact ones, esters, etc.) and real samples of environmental, medical, and technic al relevance (ozonized PAHs, lake water, human urine, diesel exhaust conden sates). The retention times of the investigated aromatics exhibit a regular increase with molecular mass and a systematic decrease with increasing num ber and polarity of functional groups. In case of intramolecular hydrogen b onding, a positive shift of retention time provides additional structural i nformation. The combination of chromatographic retention time with the mole cular mass and structural information from mass spectrometric detection all ows the tentative identification of unknown aromatic analytes at trace leve ls, even without specific reference substances. With atmospheric pressure c hemical ionization (APCI), low detection limits and highly informative frag mentation patterns can be obtained by in-source collision-induced fragmenta tion in a single-quadrupole LC-APCI-MS system as applied in this study, and multidimensional MS experiments are expected to further enhance the potent ial of the presented method.