A simple, versitile approach for coupling a liquid chromatograph and chemical ionization mass spectrometer for offline analysis of organic aerosol

Abstract. A method is described for coupling a high-performance liquid chromatograph (HPLC) and chemical ionization mass spectrometer (CIMS) for offline analysis of organic aerosol. It employs a nebulizer interface and an Aerodyne Vaporization Inlet for Aerosols (VIA), allowing for the transmission of analytes from the HPLC eluent into the CIMS inlet. Performance of the HPLC-VIA-CIMS system was assessed through analysis of carboxylic acid standards, environmental chamber-generated secondary organic aerosol (SOA) formed from the ozonolysis of α-pinene, and ambient OA collected at an urban setting. Chromatographic peak shapes were retained through nebulization and evaporation, providing baseline-resolved separation of C₆-C₁₈ carboxylic acids and generating molecular-level detail that is not attainable using HPLC or CIMS alone. Instrument response was found to be linear (R²>0.97) over an order of magnitude (0.2–3.0 nmol or 2–30 nmol) for each of the 12 standards. Analysis of α-pinene ozonolysis SOA achieved isomer-resolved detection of both monomer and dimer reaction products and, through the use of a diode array detector (DAD), illustrated the preservation of chromatographic peak shape through nebulization and evaporation. The HPLC-VIA-CIMS instrument also shows potential for quantitative analysis, provided that authentic standards can be purchased or synthesized, and semiquantitative analysis of UV-absorbing compounds such as nitrates and carboxylic acids by using a DAD. The system is compatible with small sample quantities (e.g., 30 μg of α-pinene ozonolysis SOA), allowing for detailed molecular characterization of field-collected SOA, including the identification of several monoterpene oxidation products.