Abstract Determination of Cu, Pb, Cd and Zn was per- formed in sediment extracts obtained according to the three steps sequential extraction procedure proposed by the European Community Standards, Measurements and Testing Program. The metal content was determined by anodic stripping voltammetry with a thin mercury film electrode controlled by a sequential injection (SIA) sys- tem. The proposed method improved the reproducibility of conventional anodic stripping voltammetry, as well as the sample throughput, allowing analysis of 30 to 45 samples per hour. The influence of flow rate and sample volume was studied to achieve an adequate sensitivity for the leachate studied. No interferences due to adsorption of or- ganic matter, colloids, or complexes with slow rate of dis- sociation were observed. The intermetallic formation of Cu-Zn was avoided by forming the mercury film in pres- ence of Ga(III) ions in the SIA system, resulting in low consumption of reagent in comparison to flow injection or continuous flow systems. Results were in good agreement with those obtained by Induced Coupled Plasma – Atomic Emission Spectroscopy (ICP- AES). Introduction Anodic stripping voltammetry is a very sensitive multiele- mental technique for determination of heavy metals, where a pre-concentration step is performed by deposition of analytes on the hanging mercury drop electrode (HMDE), or thin mercury film electrode (TMFE) [1]. When the technique is applied in the batch mode, the an- alytical throughput is low, since deaeration, electrolytic deposition, resting or equilibration and the potential scan are necessary steps in the experiment. Reliable and repro- ducible results are obtained if it is possible to reproduce with high precision the conditions of mass and charge transport, that requires very reproducible electrode sur- face area, stirring and time control. In fresh waters and sediment extracts, the size and shape of the ASV peak is influenced by the chemical composition of the extract and may be dependent on adsorption processes, rate of com- plex dissociation and formation of intermetallic com- pounds [2, 3]. Because of these characteristics, methods based on atomic spectroscopy are often preferred for ser- ial determination of metals in waters or sediment extracts, despite the higher costs of spectrometers compared to po- tentiostats. The highly reproducible flow patterns obtained in flow injection (FIA) systems have been used for anodic strip- ping voltammetry, permitting a precise time control and reproducible conditions of charge and mass transport [4–12]. Recently, Ivaska and Kubiak [13] proposed the automation of anodic stripping voltammetry by sequential injection analysis (SIA) to perform the in-situ mercury film formation, sample injection, and the medium ex- change in the stripping step in order to improve the selec- tivity of the measurements. Sequential injection analysis is a robust flow analysis technique that meet the requirements of industrial process and environmental monitoring, with minimal needs for maintenance and recalibration. The principles of repro- ducible time and mixing in SIA are similar to those of FIA. The system is consisting of a syringe pump con- nected by a holding coil to the starting port of a multi-port selection valve. This starting port can access, by electrical actuation, each one of the other ports, which are con- nected to reagents, samples, standards, reaction/dilution coils and detectors. The system is computer controlled and, on operation, the syringe pump aspirates reagents and sample into the holding coil. Reversing the flow, the mixture zone is injected in the reaction coil and the detec- tor flow cell at a pre-programmed flow rate. An interest- ing feature of SIA is that different conditions of analysis, or sample preparation (dilution, pre-concentration, sensor conditioning), may be performed with minimal or even none mechanical reconfiguration, which is very useful for complete analysis automation. Clóvis L. da Silva · Jorge C. Masini Determination of Cu, Pb, Cd, and Zn in river sediment extracts by sequential injection anodic stripping voltammetry with thin mercury film electrode Fresenius J Anal Chem (2000) 367 : 284–290 © Springer-Verlag 2000 Received: 18 October 1999 / Revised: 14 December 1999 / Accepted: 19 December 1999 ORIGINAL PAPER C. L. da Silva · J. C. Masini () Instituto de Química, Universidade de São Paulo, Caixa Postal 26.077, 05599-970, São Paulo, SP, Brazil e-mail: jcmasini@quim.iq.usp.br