STRIPPING POTENTIOMETRY FOR ORGANOLEAD COMPOUNDS - APPLICATION TO THE DETERMINATION OF TOTAL LEAD IN GASOLINE

A 10-mu-l gasoline sample is added to 590-mu-l of a modifying matrix composed of 1.5 g l-1 mercury(II), 0.50 M nitric acid and 1% (v/v) Triton X-100 in 90% ethanol. Tetraethyl- and/or tetramethyllead (TEL and TML, respectively) are reduced and simultaneously amalgamated on a glassy carbon electrode employing a pulsed electrolysis sequence, and the amalgamated lead is re-oxidized by means of a constant current. One analysis, which is performed automatically under computer control with a commercial potentiometric stripping analyser, takes approximately 5 min including the time for sample preparation and result evaluation. The system is calibrated by means of a single-point calibration using a standard prepared in isooctane and containing 15 mg l-1 of lead, half from TEL and half from TML. The relative difference in sensitivity between TEL and TML is 8%, in accordance with theory. The method is best suited for unleaded gasoline with total lead concentrations in the range 0.1-30 mg l-1 of total lead. The results obtained agree well with those obtained by atomic absorption spectrometry. The estimated precision is 4-8% (R.S.D.) and the detection limit 0.07 mg l-1 of total lead.