Abstract The hyphenation of gas-diffusion separation and ion chromatography (IC) is described as a convenient, reliable, robust, and economic method for in-line sample pre-treatment. The high selectivity associated with this method permits direct analysis of samples containing mi- croparticulates, colloidal matter, and/or high molecular weight compounds. The determination of sulfite serves as a first example of its application. The method is based on the diffusional separation of SO 2 following in-line oxida- tion with hydrogen peroxide to sulfate and final determi- nation of the sulfate formed using IC. The influence of operational parameters has been thoroughly investigated and gas-diffusion cells of different geometries compared with respect to the gas-transfer rates obtained. Application to the analysis of wines demonstrates the utility of the method. Introduction Ion chromatography is a highly versatile method for the determination of many ions in a large variety of samples. However, samples containing particulate matter and/or constituents that are capable of poisoning the stationary phase must be removed prior to sample injection by ap- propriate means. To this end, (costly and cumbersome) microfiltration and solid-phase extraction are generally employed [1, 2]. Although they offer many beneficial fea- tures, membrane-based sample preparation techniques have only recently attracted attention as viable alternatives [3, 4]. A particularly interesting feature of membrane separa- tion is its ability to be performed continuously in a flow system. This enables sample preparation to be performed in-line with inherent automation capabilities. The use of dialysis [5, 6, 7] and membrane extraction [8, 9] has been described in hyphenation with gas and liquid chromatog- raphy, demonstrating efficient sample clean-up, high se- lectivity, and applicability to a wide variety of analytes. In certain configurations these techniques have also been used as means for analyte preconcentration. To the best of our knowledge the in-line coupling of gas-diffusion sepa- ration and ion-chromatography has so far only been re- ported in two papers on the determination of total and la- bile cyanide in waters [10] and on the determination of ammonia and methylamines in seawater and precipitates [11]. Both papers describe ingenious, yet rather compli- cated means of sample manipulations using several switch- ing valves and intermittent pumping of the respective so- lutions, whereas the operational parameters affecting sen- sitivity and selectivity have not been studied in detail. In this paper we present the results of a thorough in- vestigation of gas-diffusion separation in hyphenation with ion-chromatography. A simple to operate, yet robust and extremely flexible system is described. As an exam- ple of this widely applicable system, sulfite has been se- lected as a model compound for various reasons. First, our previously gained experience in the gas-diffusion of sul- fite in flow injection analysis [12, 13] permitted straight- forward optimization of the experimental parameters re- lated to the separation step. Secondly, ion-chromato- graphic determination of sulfite is handicapped by the low stability of sulfite which (if not converted to hydroxy- methanesulfonate by the addition of formaldehyde) is readily oxidized to sulfate; partial oxidation also occurs on-column during the chromatographic separation [14]. This complicates the simultaneous determination of sul- fate and sulfite. Thirdly, sulfite is a frequently determined compound in a wide variety of industrial and food sam- ples, where sample clean-up is often mandatory. Finally, most standard methods for the determination of sulfite are time consuming and tedious manual methods, including distillation and titration or spectrophotometric determina- Sara Fäldt · Bo Karlberg · Wolfgang Frenzel Hyphenation of gas-diffusion separation and ion chromatography Part 1: Determination of free sulfite in wines Fresenius J Anal Chem (2001) 371 : 425–430 DOI 10.1007/s002160101081 Received: 12 June 2001 / Revised: 14 August 2001 / Accepted: 14 August 2001 / Published online: 14 September 2001 SPECIAL ISSUE PAPER S. Fäldt · B. Karlberg Department of Analytical Chemistry, Stockholm University, 10691 Stockholm, Sweden W. Frenzel (✉) Technische Universität Berlin, Institut für Technischen Umweltschutz, Strasse d. 17. Juni 135, 10623 Berlin, Germany e-mail: frenzel@itu101.ut.tu-berlin.de © Springer-Verlag 2001