Aldehyde-selective polymeric membrane electrodes based on a calix[4]arene ionophore

A novel type of aldehyde-selective electrode was designed based on the host-guest interaction between p-tert-butylcalix[4]arene ionophore and hydrazone generated in situ from heptanal and Girard's reagent P. The poly(vinyl chloride) membrane electrode contains 3.5-8% m/m of a tetraester derivative of calix[4]arene as the neutral carrier and dioctyl phthalate as the plasticizer. At pH 5.5, the electrode exhibits a Nernstian response in the range 1 × 10^-2-9 × 10^-7 mol l^-1 heptanal with a slope of 67.7 mV per concentration decade. The electrode has a fast response time and a constant Nernstian response after 2 months of continuous measurement. The viability of using the electrode for the micro-determination of heptanal was also demonstrated. The minimum detectable concentration of aldehyde is 3 × 10^-5 mol l^-1, or, as little as 3.4 μg of heptanal can be determined accurately by the method.