Sol–gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

AbstractA niobia‐based sol–gel organic–inorganic hybrid sorbent carrying a positively charged C18 ligand (Nb2O5‐C18(+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high‐performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid–base, and van der Waals interactions. To understand relative contributions of various molecular level analyte–sorbent interactions in the extraction process, two other sol–gel niobia sorbents were also created: (a) a purely inorganic sol–gel niobia sorbent (Nb2O5) and (b) an organic–inorganic hybrid sol–gel niobia sorbent carrying an electrically neutral‐bonded octadecyl ligand (Nb2O5‐C18). The extraction efficiency of the created sol–gel niobia sorbent (Nb2O5‐C18 (+ve)) was compared with that of analogously designed and synthesized titania‐based sol–gel sorbent (TiO2‐C18 (+ve)), taking into consideration that titania‐based sorbents present state‐of‐the‐art extraction media for organophosphorus compounds. In capillary microextraction with high‐performance liquid chromatography analysis, Nb2O5‐C18 (+ve) had shown 40–50% higher specific extraction values (a measure of extraction efficiency) over that of TiO2‐C18 (+ve). Compared to TiO2‐C18(+ve), Nb2O5‐C18(+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed‐phase high‐performance liquid chromatography mobile phase.