Functionalized graphene oxide tablets for sample preparation of drugs in biological fluids: Extraction of ritonavir, a HIV protease inhibitor, from human saliva and plasma using LC–MS/MS

In this work, graphene oxide–based tablets (GO‐Tabs) were prepared by applying a thin layer of functionalized GO on a polyethylene substrate. The GO was functionalized with amine groups (–NH2) by poly(ethylene glycol)bis(3‐aminopropyl) terminated (GO‐NH2‐PEG‐NH2). The functionalized GO‐Tabs were used for the extraction of ritonavir (RTV) in human saliva samples. RTV in plasma and saliva samples was analyzed using LC–MS/MS. Gradient LC system with MS/MS in the positive‐ion mode [electrospray ionization (ESI+)] was used. The transitions m/z 721 → 269.0 and m/z 614 → 421 were used for RTV and the internal standard indinavir, respectively. This study determined the human immunodeficiency virus protease inhibitor RTV in human saliva samples using functionalized GO‐Tab and LC–MS/MS, and the method was validated. The standard calibration curve for plasma and saliva samples was constructed from 5.0 to 2000 nmol L−1. The limit of detection was 0.1 nmol L−1, and the limit of quantification was 5.0 nmol L−1 in both plasma and saliva matrices. The intra‐ and inter‐assay precision values were found to be between 1.5 and 5.8%, and the accuracy values ranged from 88.0 to 108% utilizing saliva and plasma samples. The extraction recovery was more than 80%, and the presented functionalized GO‐Tabs could be reused for more than 10 extractions without deterioration in recovery.