AUTOMATED SAMPLE PREPARATION FOR THE DETERMINATION OF BUDESONIDE IN PLASMA SAMPLES BY LIQUID-CHROMATOGRAPHY AND TANDEM MASS-SPECTROMETRY

An automated bioanalytical method for the determination of the glucoco rticosteroid drug budesonide in plasma samples at pM levels was invest igated. The method was built using three separate automated analytical steps with manual transfer of samples between them. In the first step , a Tecan RSP150 (Genesis) pipetting robot was used to transfer 1 mi o f centrifuged plasma samples and deuterated budesonide internal standa rd solutions into tubes and to homogenise the resulting admixture. In the second step, a solid-phase extraction was performed using an ASPEC Xli (Gilson) with 100 mg Isolute C-18 columns. In order to avoid conv entional time-consuming evaporation and reconstitution steps, the soli d-phase extraction was coupled on-line to a trace enrichment system fo r further purification and concentration of the sample extracts. The c oncentrated samples were eluted in 300 mu l ethanol into injection via ls, which were capped and transferred to the autosampler in the detect ion system In the third step, the pre-treated samples were chromatogra phed in a gradient LC system and detected using a tandem MS system (Fi nnigan TSQ 7000), with an atmospheric pressure chemical ionisation int erface. The described Analytical System consisting of one Tecan robot, two ASPEC systems and one LC-MS-MS system may analyse up to about 800 samples a week with less routine work for the analyst. The concentrat ion range studied was 15 to 2500 pM in 1 ml spiked plasma samples and the limit of quantitation for the described method was determined as 1 5 pM, as defined by accuracy and precision better than 20%. (C) 1998 E lsevier Science B.V. All fights reserved.