Liquid chromatography–atmospheric pressure laser ionization–mass spectrometry (LC-APLI-MS) analysis of polycyclic aromatic hydrocarbons with 6–8 rings in the environment

Jan B. Thiäner, Christine Achten

A method has been developed for the sensitive and rapid analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples using liquid chromatography time-of-flight mass spectrometry as well as the selective atmospheric pressure laser ionization (APLI) process (LC-APLI-MS). Upon analyzing 34 PAHs, the limits of detection of this method were found to range from 0.008 to 1.824 pg (0.024 pg for benzo[a]pyrene). The method therefore provides 30-fold to 5,400-fold increased sensitivity compared with the established GC-MS technique. This LC-APLI-MS method was optimized for higher molecular weight PAHs (C24-C30 PAHs with 6-8 rings), which are difficult to detect or cannot be detected by GC-MS. Using the LC-APLI-MS method, various 6- to 8-ring PAHs were detected in environmental samples for the first time. After developing the method, it was successfully validated in ruggedness tests. The concentrations determined by the LC-APLI-MS method were in good accord with the certified concentrations in three certified reference materials (contaminated soils and sediments). Upon applying the method to environmental samples, it was found that (1) the presence of dibenzo[a,i]pyrene and dibenzo[a,h]pyrene in urban soil samples could only be detected using LC-APLI-MS (i.e., not GC-MS) due to its high sensitivity, (2) a bituminous coal sample yielded 211 tentative peaks from aromatic compounds in the C24-C30 range, and (3) eleven of those compounds occurred in different environmental samples in similar patterns. Hence, 6- to 8-ring PAHs occur in solid environmental samples in which other 6-ring PAHs such as indeno[1,2,3-cd]pyrene or benzo[ghi]perylene may also be present. Some of these numerous higher molecular weight PAH compounds could have very high carcinogenic potential, which will need to be elucidated to ensure the reliability of PAH risk assessments.