Research Article

SPE-UHPLC-FLD Method for the Simultaneous Determination of Five Anthraquinones in Human Urine Using Mixed-Mode Bis(tetraoxacalix[2]arene[2]triazine) Modified Silica as Sorbent

Figure 2

Preparation scheme of bis(tetraoxacalix[2]arene[2]triazine)-modified silica gel SPE sorbent (BTO-SPE).