Amino-attapulgite/mesoporous silica composite films generated by electro-assisted self-assembly for the voltammetric determination of diclofenac

Diclofenac (DCF) is a common anti-inflammatory drug. In this work, we have developed two new modified electrodes based on attapulgite clay mineral for the determination of DCF. The first one is made of an amino-functionalized attapulgite modified glassy carbon electrode (GCE/Amino-AT) issued from the grafting of attapulgite particles with [3-(2-aminoethylamino) propyl] trimethoxysilane. Voltammetric data indicate slightly easier oxidation of DCF on such modified electrode (irreversible anodic peak at +0.750 V vs. Ag/AgCl i.e., about 85 mV lower than on bare GCE), and pH-dependent response resulting from interactions between the probe and the electrode material. The second one is an amino-attapulgite-mesoporous silica composite film generated by electro-assisted self-assembly of a surfactant-templated silica layer entrapping the amino-functionalized attapulgite particles on GCE pretreated by electrografting of [3-aminopropyl] triethoxysilane (GCE/APTES-Amino-AT-Silica), which was designed in order to avoid the loss of clay particles in solution over prolonged use of the modified electrode. After characterization of the film morphology, composition and permeability, respectively by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV), the modified electrodes were applied to the detection of DCF by square wave voltammetry (SWV). Both electrodes gave rise to SWV peak currents varying linearly with DCF concentration in the range of 0.3-20 mu M (in phosphate buffer at pH 5.7). The detection limits were 0.204 mu M on GCE/Amino-AT and 0.053 mu M on GCE/APTES-Amino-AT-Silica. The proposed method was successfully applied to the determination of DCF in pharmaceuticals and water samples.