Microextraction in packed syringe online with liquid chromatography-tandem mass spectrometry: Molecularly imprinted polymer as packing material for MEPS in selective extraction of ropivacaine from plasma

The excellent performance of a new sample preparation method, microextraction in packed syringe (MEPS), was recently illustrated by online LC-MS and GS-MS assays of local anaesthetics in plasma samples. In the method, approximately 1 mg of solid packing material was inserted into a syringe (100-250 mu L) as a plug. Sample preparation took place on the packed bed. The new method was easy to use, fully automated, of low cost, and rapid in comparison with previously used methods. This paper presents the use of molecularly imprinted polymers (MIPs) as packing material for higher extraction selectivity. Development and validation of a method for MIP-MEPS online with LC-MS-MS using ropivacaine in plasma as model compound were investigated. A bupivacaine imprinted polymer was used. The method was validated and the standard curves were evaluated by means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 2-2000 nM. The applied polymer could be used more than 100 times before the syringe was discarded. The extraction recovery was 60%. The results showed high correlation coefficients (R-2 > 0.999) for all runs. The accuracy, given as a percentage deviation from the nominal concentration values, ranged from -6% to 3%. The precision, given as the relative standard deviation, at three different concentrations (QC samples) was consistently about 3% to 10%. The limit of quantification was 2 nM.