Sono-Electroanalysis: Application to the Detection of Lead in Petrol

Abstract

The quantitative detection of lead in petrol is shown to be possible by anodic stripping voltammetry in aqueous media under conditions of insonation-induced emulsification. An immersion horn probe is introduced into a thermostatted conventional three-electrode cell opposite a mercury plated platinum disk working electrode. Under ultrasonic emulsification of the sample, lead is preconcentrated as an amalgam on the Hg/Pt electrode surface via reduction at –1.0 V (vs. SCE). The large mass transport associated with power ultrasound makes this step highly efficient. Subsequently the lead is quantified by applying an anodic linear sweep of the potential from –1.0 V to –0.15 V (vs. SCE) so as to oxidize the Pb(0) to Pb(II). The area under the stripping peak gives a measure of the lead formed during the initial step. By use of standard microaddition of lead to the solution the system can be calibrated to give the total amount of lead present in the petrol sample. Experiments using samples of 4 star leaded petrol gave a total lead content of 380±40 mgL–1. This value was in quantitative agreement with that obtained by an independent laboratory using atomic absorption spectroscopy (AAS). In addition to the high mass transport and emulsification insonation offers the crucial benefits of first surface activation and cleaning, helping to prevent electrode fouling by the organic components of petrol and second the complete extraction of lead from the water-insoluble target phase.