FLAME-BASED THERMIONIC DETECTION COUPLED ONLINE WITH MICROCOLUMN LIQUID-CHROMATOGRAPHY .1. OPTIMIZATION OF THE SYSTEM

A thermionic detector originally developed for gas chromatography was coupled with microcolumn (0.3 mm I.D.) liquid chromatography. For coupling, an interface used previously for flame photometric detection was used. Minor modifications to the burner head and detector were necessary. The eluent and analyte introduction were studied by varying parameters such as the air, hydrogen and helium gas flow-rates and the rubidium source-burner rim distance. To obtain stable eluent and analyte introduction. a minimum flame length of about 6 mm was required. A near-stoichiometric H-2:O2 ratio was found to give optimum detector sensitivity; the optimum rubidium source-burner rim distance and hydrogen flow-rate were mutually dependent. The system was used for the determination of organophosphorus compounds, e.g., the pesticide dichlorvos and its polar non-volatile metabolite dimethylphosphoric acid and the herbicide glyphosate. For the analytes tested, the detection limit was 10-20 pg/s of phosphorus.