A measurement method for atmospheric ammonia and primary amines based on aqueous sampling, OPA derivatization and...

A method of precolumn derivatization HPLC with fluorescence detection has been developed for the measurement of ammonia, primary methylamine, ethylamine, propylamine, and butylamine in the atmosphere. Air samples were collected by two continuously wetted glass frit/coil samplers, one directly from ambient air for the sum of gaseous and aerosol species, and the other after an acid-coated annular denuder for the aerosol species. The collection efficiency for all analytes was found to be > or = 99% at a sampling gas flow rate of 2 L min(-1) and a scrubbing water flow rate of 0.24 mL min(-1). The collected ammonia and primary amines were derivatized with o-phthalaldehyde (OPA) and n-acetyl-cysteine (NAC) reagents in an in-line derivatization coil to form highly fluorescent sulfonatoisoindole derivatives. Detailed kinetic study showed that derivatization reactions were fast but the derivatives were not very stable. Derivatization conditions, such as reagent concentrations, derivatication medium pH, and derivatization time, were optimized to achieve maximum derivative yields for all the analytes. The derivatives were separated on a C-18 reverse-phase column using a gradient elution and detected by a fluorescence detector at an excitation wavelength of 330 nm and an emission wavelength of 471 nm. The respective lower detection limits for ammonia and for the four primary amines were 24 parts per trillion by volume (pptv) and < or = 3 pptv, with a sample time resolution of about 1 min and a sampling/ analysis time of 20 win per cycle. The analytical methodology has been applied in the field measurements; results from two case studies are presented.