Evaluation of Solid-Phase Microextraction in Combination with Gas ( ) Chromatography SPME-GC as a Tool for Quantitative Bioanalysis Mohamed Abdel-Rehim, Margareta Bielenstein, Torbjorn Arvidsson ¨ Astra Pain Control AB, SE-151 85 Sodertalje, Sweden ¨ ¨ Received 27 August 1999; revised 21 January 2000; accepted 21 January 2000 Abstract: Solid-phase microextraction in combination with capillary gas chro- matography and a nitrogen phosphorus detector as a bioanalysis tool was investi- gated. Lidocaine and three of its metabolites were used as model compounds, and human plasma and urine samples were used in this evaluation. Carbowax divinyl- benzene, polyacrylate, and polydimethylsiloxane fibers were tested. Absorption times were studied for all analytes separately. Carbowax divinylbenzene fiber gave highest recovery in plasma samples compared to other fibers. Effects of tempera- ture, addition of salt and agitation of the sample were studied. Recovery from plasma was improved by 2 4 times at pH 9 compared to pH 3. This is due to analytes not charged at high pH. Recovery from water was 2 4 times higher than from plasma using Carbowax divinylbenzene coated fiber. This is due to protein binding of analytes in plasma. Chromatographic selectivity was high and all metabolites were well separated. Calibration curves were linear for all metabolites in human plasma and urine in the range 0.035 7.7 M for lidocaine and 2,6-xyli- Ž . dine while 0.1 3.5 M for glycinexylidide GX and monoethylglycinexylidide Ž . MEGX . Precision, measures as relative standard deviation, was less than 15% and accuracy was in the range 80 115%. Limits of quantitation using plasma were Ž . Ž . Ž . 0.035 M 8ngmL , 0.035 M 4ngmL , 0.100 M 18 ngmL , and 0.100 M Ž . 21 ngmL for lidocaine, 2,6-xylidine, GX, and MEGX, respectively. 2000 John Wiley & Sons, Inc. J Micro Sep 12: 308 315, 2000 INTRODUCTION Ž . Solid-phase microextraction SPME is a simple sample-preparation method for gas and liquid chro- Ž . matography GC, LC that has been used mainly for the analysis of aqueous samples of environmental pollution 1 5 . This extraction technique has many advantages such as no use of solvent, easy handling, a relatively short extraction time, easy automation, and high linearity for many analytes. The extraction is based on the partitioning of the analyte between Ž the fiber coating Carbowax or polydimethylsilox- . Ž ane and the matrix air, water, soil, plasma, or . urine . The distribution of a solute between two phases depends on the physical and chemical inter- actions between the solute and the polymer phases. The partition equilibrium may be affected by factors such as pH, temperature, salts, and stirring. Sample-preparation is an important part in the analysis of pharmaceutical compounds in body flu- Correspondence to: Mohamed Abdel-Rehim. ids. The aim for the sample-preparation method is to eliminate interfering from the biological samples, to be reproducible, easy handling, easy automation, and requires a minimum number of steps. Different types of sample-preparation were tested using lido- caine and its metabolites. Liquid liquid extraction Ž . Ž . LLE and solid phase extraction SPE takes more time and more steps compared to SPME. However, for drug analysis in body fluids the SPME is still under test. Few publications with SPME involving drugs and their metabolites in human urine or plasma has been reported 6 16 . In the present application, the SPME is tested for lidocaine and its metabolites as a sample-preparation for urine and plasma samples and the method is validated. Lidocaine, an amide-type local anesthetic, is widely used in anesthesiology. It also has antiar- rhythmic properties and is frequently used as a therapeutic agent in the treatment of cardiac disor- ders. The major metabolites of lidocaine are conju- Ž . gated 4-hydroxy-2,6-xylidine 4-OH-XYL , 2,6-xyli- Ž . Ž . dine 2,6-XYL , monoethylglycinexylidide MEGX , Ž. Ž . J. Microcolumn Separations , 12 5 308 315 2000 2000 John Wiley & Sons, Inc. 308