Ion-selective electrodes based on calix[4]arene tetraester in the determination of formaldehyde via in situ generation of ionic lipophilic hydrazone

A formaldehyde-selective electrode was designed based on the host-guest interaction between p-tert-butylcalix[4]arene tetraester and lipophilic hydrazone generated in situ from formaldehyde and a modified Girard's reagent G2. The poly(vinyl chloride) membrane electrode contains 4.5% m/m of a tetraester derivative of calix[4]arene as the neutral carrier and dioctyl phthalate as the plasticizer. At pH 5.4, the electrode exhibits a dicationic Nernstian response in the range 4 × 10-5-0.1 mol l-1 formaldehyde with a slope of 32.4 mV per decade. In contrast, at pH 9.2, the electrode shows a near Nernstian response with a slope of 50.3 mV per decade in a narrower working concentration range. The electrode has a fast response time and a long working lifetime. The viability of using the electrode for the micro-determination of formaldehyde was also demonstrated.