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

In this study, we synthesized a new hybrid material using well-Dawson K₆P₂Mo₁₈O₆₂]·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 ∼0 V 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 ∼63 nA/μM AA, fast response time (<9 s), low detection limit (<0.1 μM), high selectivity towards endogenous interferences such as uric acid, acetaminophen and dopamine, a linear range from 0.1 μM to at least 22 mM AA and was stable for at least 2 weeks. In addition, such AA sensors can operate in a pH range from 0 to at least 7.