68 trends in analytical chemistry, vol. 13, no. 2, 1994 zyxwvutsrqp C o ntinuo us liq uid - liq uid e xtra c tio n a nd d e riva tiza tio n module coupled on-line with g a s c hro m a to g ra p hic d e te c tio n M. ValcBrcel*, E. Ballesteros and M. Gallego Cchdoba, Spain The combined use of a gas chromatograph and a continuous sample pretreatment mod- ule based on liquid-liquid extraction for automatic conditioning of samples (precon- centration, dilution, derivatization, solvent changeover) has a great, scarcely explored potential. Existing applications of this hy- phenated methodology and foreseeable trends are discussed. Introduction The preliminary operations of the analytical process can be improved through simplification, automatization and miniaturization [ 11. This has been acknowledged by instrument manufacturers, who are beginning to commercialize off-line and on-line instrumentation for establishing a fluent link between the unsampled, untreated, unmeas- ured material to be analysed and detection. Chromatographic techniques (including on-line detection) and methods are quite commonplace in laboratories devoted to routine analyses, particu- larly organic analyses. Commercially available chromatographs have reached rather impressive performance levels in the last few years, as have the chemometric methodologies for data process- ing. However, most gas, liquid and solid samples require some pretreatment because they are too complex and/or incompatible with the chroma- tographic system used, and the analyte concentra- tions are too low or high. Collection, storage, extraction, dilution, concentration, isolation, sol- vent changeover, etc. are customary preliminary *To whom correspondence should be addressed. 01659936/94/$07.00 operations of chromatographic analysis [2]. They involve a high degree of human participation and are rather time-consuming and a source of major errors that affect the quality of analytical results and can occasionally be hazardous. Any steps taken to overcome these drawbacks are thus worthwhile. Non-chromatographic continuous separation techniques [3] based on mass transfer through a fixed or mobile liquid-gas, liquid-liquid or solid- liquid interface offer clear advantages over con- ventional/manual approaches, namely: l easy implementation in modules coupled on- line with column chromatographs (gas chroma- tography, GC; high-performance liquid chromatography, HPLC; supercritical fluid chromatography, SFC); l reduction of hazards involved in the manipula- tion of toxic reagents and solvents; l increased precision resulting from automation and simplification; l increased sample throughput; l reduced sample and reagent consumption through miniaturization; and . lower analytical costs. The performance of analytical separation tech- niques coupled on-line with chromatography (GC, HPLC, SFC) depends on the state of aggregation of the sample. Solid samples are particularly well handled by supercritical fluid extraction coupled on-line with any of the three chromatographies [4]. Gaseous samples are most often processed by a mixed off/on-line approach involving collection of the analytes in sorption tubes and subsequent on- line treatment by the gas chromatograph using a programmed thermal desorption module [2]. Liq- uid samples are highly compatible with on-line coupled HPLC systems (e.g., dialysis, liquid-liq- uid extraction, sorption) [3]; however, they are more difficult to introduce directly into GC and SFC owing, among other factors, to incompatibil- ity of the sample matrix (e.g. water) and the sepa- ration system. 0 1994 Elsevier Science B.V. All rights reserved