Solid-Phase Microextraction: Artefact Formation and its Avoidance H. Verhoeven 1 / T. Beuerle 2 / W. Schwab 2. 1 Centrum voor Plantenveredelings- en Reproduktieonderzoek (CPRO-DLO), P.O.Box 16, 6700 AA Wageningen, The Netherlands 2 Lehrstuhl ftir Lebensmittelchemie, Universit~it Wtirzburg, Am Hubland, 97074 Wtirzburg, Germany Key Words Solid-phase microextraction Artefact formation Strawberry flavour analysis Summary The application of solid-phase microextraction (SPME) for the flavour analysis of strawberry and apple fruits has been studied. An SPME liquid sampling method based on poly(acrylate)-coated fibers was developed. Immediate thermal desorption of the adsorbed com- pounds led to the formation of Maillard products due to the high concentration of carbohydrates and amines in the samples, remaining on the surface of the fiber. Arte- fact formation was significantly reduced by rinsing the fiber with water prior to thermal desorption. The SPME liquid sampling and headspace method (HS- SPME) has been studied mainly for pollutants [3, 4, 7-10]. Recently, HS-SPME has also been applied for the analysis of flavour compounds [11] from hop [12], truffle [13], coffee [14], and strawberry fruits [15]. As several aroma-intensive flavour compounds occur only in trace amounts in the headspace and are rarely adsorbed by the fiber coating [14], we decided to apply SPME liquid sampling for the flavour analysis of fruits and beverages. This paper focuses on the development of a method to qualitatively determine certain flavour volatiles present in strawberries and apples. Experimental Samples Freshly picked strawberries (cv. Elsanta) and apples (cv. Elstar) were obtained from CPRO-DLO, Wageningen, The Netherlands. Introduction Solid-phase microextraction (SPME) is a fast, sol- ventless alternative to conventional sample extraction techniques developed by Pawliszyn and co-workers [1-5]. The procedure employs a stationary phase coated on a fused silica fiber to concentrate trace compounds from the sample matrix. When the SPME fiber is im- mersed in an aqueous sample or is extended into its headspace, a partitioning of the compounds in the sam- ple between either the aqueous phase or the gas phase, and the fiber surface occurs. The adsorbed compounds can then be thermally desorbed in a gas chromatograph (GC) injection port [6]. Solid-Phase Microextraction (SPME) The SPME device was purchased from Supelco Inc. (Bellfonte, PA, USA), as was the fused silica fibre coated with 85 pm polyacrylate. For liquid sampling, the SPME fiber was inserted into an intact fruit or ho- mogenate of the fruit. The fiber remained in the fruits or homogenate for 30 s and was then either immediately introduced into the GC injection port or rinsed with wa- ter prior to thermal desorption. For comparison, one strawberry (6 g) was homogenized after addition of liquid N2 in a mortar. The homogenate was subjected to SPME liquid sampling and then ex- tracted three times with 1 mL of diethyl ether. After drying over sodium sulphate the solvent was carefully removed to 50 gL by a gentle nitrogen stream. Original Chromatographia Vol. 46, No. 1/2, July 1997 63 0009-5893/97/07 63-04 $ 03.00/0 9 1997 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH