An etched polyether ether ketone tube covered with immobilized graphene oxide for online solid phase microextraction of quaternary alkaloids prior to their quantitation by HPLC-MS/MS

Polyether ether ketone (PEEK) is an ideal substrate for in tube solid-phase microextraction (SPME) because it overcomes the shortcomings of conventional silica fibers in terms of fragility and poor flexibility. Commonly used bare PEEK tubes suffer from difficult modification with selective sorbents and low inner surface areas. This problem was solved by etching with concentrated sulfuric acid, which dissolves the amorphous regions of the PEEK surface and yields a rough inner surface with plenty of microscopically small holes. The etched tube was then stepwise functionalized with polydopamine and graphene oxide which was in-situ immobilized. The modified tube displays excellent efficiency for the extraction of positively charged quaternary alkaloids by a mixed-mode extraction. Enrichment factors from 221 to 275 can be obtained for the extraction of the alkaloids jatrorrhizine, palmatine and berberine. The alkaloiods were then quantified by online SPME-HPLC-MS/MS detection. The method has detection limits of 0.1 pg mL−1, good linearity, and good intra-day reproducibility (≤ 2.4%). It was applied to the analysis of the three alkaloids in Cortex Phellodendri herb and rat plasma after oral administration.