A wooden stick coated with a novel graphene-based nanocomposite (Graphene\noxide/polyethylene glycol (GO/PEG)) is introduced and investigated for its efficacy in solid\nphase microextraction techniques. The GO/PEG-stick was prepared and subsequently applied\nfor the extraction of Beta-blockers, acebutolol, and metoprolol in human oral fluid samples, which\nwere subsequently detected by liquid chromatography tandem mass spectrometry (LC-MS/MS).\nExperimental parameters affecting the extraction protocol including sample pH, extraction time,\ndesorption time, appropriate desorption solvent, and salt addition were optimized. Method\nvalidation for the detection from oral fluid samples was performed following FDA (Food and\nDrug Administration) guidelines on bioanalytical method validation. Calibration curves ranging\nfrom 5.0 to 2000 nmol L-1 for acebutolol and 25.0 to 2000 nmol L-1 for metoprolol were used.\nThe values for the coefficient of determination (R2) were found to be 0.998 and 0.996 (n = 3) for\nacebutolol and metoprolol, respectively. The recovery of analytes during extraction was 80.0%\nfor acebutolol and 62.0% for metoprolol, respectively. The limit of detections (LODs) were 1.25,\n8.00 nmol L-1 for acebutolol and metoprolol and the lower limit of quantifications (LLOQ) were\n5.00 nmol L-1 for acebutolol and 25.0 nmol L-1 for metoprolol. Validation experiments conducted\nwith quality control (QC) samples demonstrated method accuracy between 80.0% to 97.0% for\nacebutolol and from 95.0% to 109.0% for metoprolol. The inter-day precision for QC samples ranged\nfrom 3.6% to 12.9% for acebutolol and 9.5% to 11.3% for metoprolol. Additionally, the GO/PEG-stick\nwas demonstrated to be reusable, with the same stick observed to be viable for more than 10 extractions\nfrom oral fluid samples.
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