Anal. Chem. 1999, 71, 4513-4518
An Automatic Analyzer for Organic Compounds in Water Based on Solid-Phase Microextraction Coupled to Gas Chromatography C. Grote,† K. Levsen,*,† and G. Wu 1 nsch‡
Prof. Dr. Karsten Levsen Fraunhofer Institute of Toxicology and Aerosol Research Nikolai-Fuchs-Str. 1 D-30625 Hannover, West Germany, and Prof. Dr. Gerold Wu¨nsch Institute of Inorganic Chemistry, University of Hannover Callinstr. 9 D-30167 Hannover, West Germany
An automated system for quasi-continuous and on-site monitoring of organic compounds in water is presented. It is based on solid-phase microextraction (SPME) coupled to gas chromatography (GC) using a stopped-flow approach. The analytes are extracted either by direct or headspace SPME. All steps including sampling, sample preparation, extraction, chromatographic separation, and detection are fully automated. Using industrial wastewater as an example, the system was extensively validated both in the laboratory and in the field. Thus, relative standard deviations ranging from 1 to 7% were found for 24 compounds typically present in the wastewater of a chemical plant in Germany. Unattended operation of the system at a wastewater plant for more than one week is possible. Remote control via modem allows easy access to the system and the analytical data from any place. Today, organic pollutants in ground, surface, or wastewater are usually analyzed off-site in central laboratories by conventional chromatographic methods such as GC and/or liquid chromatography (LC) after off-line extraction and preconcentration by liquid-liquid extraction (LLE), solid-phase extraction (SPE), or dynamic headspace (purge and trap). These extraction methods often require toxic organic solvents or are time-consuming, expensive, or difficult to automate. For a continuous or quasicontinuous monitoring of such contaminants, automated on-site analysis is desirable. Analytical systems in which extraction is online coupled to chromatography such as SPE/GC or SPE/HPLC have been developed for this purpose.1,2 Over the past few years, solid-phase microextraction, invented by Pawliszyn in 1989,3 has become an attractive alternative to the above-mentioned conventional sampling techniques. SPME is a simple, inexpensive, and solvent-free extraction technique based on an equilibration of the analytes between the aqueous (or gas) phase and a polymeric phase. Extraction is performed by exposing * Correspondence to K. Levsen E-mail:
[email protected]. † Prof. Dr. Karsten Levsen Fraunhofer Institute of Toxicology and Aerosol Research. ‡ Prof. Dr. Gerold Wu ¨ nsch Institute of Inorganic Chemistry. (1) Bagheri, H.; Brouwer, E. R.; Ghijsen, R. T.; Brinkman, U. A. T. J. Chromatogr., A 1993, 647, 121. (2) Mol, H.; Brinkman, U. A. T. J. Chromatogr., A 1995, 703, 277. (3) Belardi, R. P.; Pawliszyn, J. Water Pollut. Res. J. Can. 1989, 24, 179. 10.1021/ac9903656 CCC: $18.00 Published on Web 09/04/1999
© 1999 American Chemical Society
a fiber coated with the polymer either directly into the aqueous sample or into the headspace above the sample. The extracted compounds are then removed from the fiber by thermal desorption into the hot injector of a GC followed by chromatographic separation and detection or, in the case of LC, by exposing the fiber to the liquid mobile phase into which the analytes are released.4-6 More than 100 reports published so far demonstrate the usefulness of SPME in water analysis, as is also summarized in two recent books.7,8 In recent years, interlaboratory comparisons have demonstrated that SPME can be used as a reliable technique for quantification of analytes down to the ppt level.9-11 The SPME technique can be easily automated using, e.g., modified GC autosamplers. However, so far the aqueous samples still have to be transported to the laboratory and the autosampler vials filled manually. In this report, a fully automated system (including sampling and sample preparation) is presented which can be operated on-site for quasi-continuous monitoring of organic pollutants in water. The system was tested using industrial wastewater (a very difficult matrix) as an example. In a preceding publication, we presented a manual SPME method for the analysis of 24 compounds commonly found in the influent of an industrial wastewater plant in Northern Germany.12 Using a polyacrylate (PA) fiber, the SPME was linear over 4 orders of magnitude. A precision of
