Selective determination of ascorbic acid with a novel hybrid material based 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and the Dawson type ion [P2Mo18O62]6− immobilized on glassy carbon

Abstract

In this study, we synthesized a new hybrid material using well-Dawson K6[P2Mo18O62]·nH2O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). CHN elemental analysis showed that one mole of [P2Mo18O62]6− reacts with 6 moles of [BMIM]+ to form [BMIM]6P2Mo18O62. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid material compared to the parent Dawson POM. The new hybrid material [BMIM]6P2Mo18O62 was immobilized on glassy carbon (GC) electrode and the modified electrode was investigated by cyclic voltammetry and amperometry. Compared to the electrochemical behavior of dissolved [P2Mo18O62]6−, a slight shift in the redox peaks towards negative potentials is observed for the immobilized [BMIM]6P2Mo18O62. The relationship between the peak currents of the deposited [BMIM]6P2Mo18O62 film and scan rate is shown to be linear, which demonstrates a surface-confined electron transfer processes. [BMIM]6P2Mo18O62 modified electrode showed high sensitivities towards pH and shown to be active even at neutral pH. [BMIM]6P2Mo18O62 modified GC electrode was subjected to cyclic voltammetry and amperometry in the presence of ascorbic acid (AA) and found to exhibit a remarkable catalytic activity towards the oxidation of AA. The catalytic oxidation peak of AA at [BMIM]6P2Mo18O62 modified GC electrode occurs at low potential of ∼0V vs Ag/AgCl at neutral pH and shifts to more positive potentials when pH decreases. Comparison between [BMIM]6P2Mo18O62 and [P2Mo18O62]6− modified GC films towards the oxidation of AA suggests that the significant decrease in the overpotentials recorded with [BMIM]6P2Mo18O62 film is related to the presence of ionic liquid cation in the hybrid material, which probably plays the role of the redox mediator. The resulting AA sensor [BMIM]6P2Mo18O62/GC has a significant sensitivity of ∼63nA/μM AA, fast response time (<9s), low detection limit (<0.1μM), high selectivity towards endogenous interferences such as uric acid, acetaminophen and dopamine, a linear range from 0.1μM to at least 22mM AA and was stable for at least 2weeks. In addition, such AA sensors can operate in a pH range from 0 to at least 7.