Amperometric flow injection analysis as a new approach for studying disperse systems

Abstract

Fast and simple quantitative determination in dispersed systems (layered double hydroxides - LDHs - suspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min-1) of 0.05 mol L-1 KNO3 solution and [Cu(H2O)6]2+, used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (-0.25 V vs Ag/AgCl/NaCl (3 mol L-1)), presents a linear relationship with [Cu(H2O)6]2+ concentration and the procedure offers high sensitivity (slope = 0.036 μA/(μmol L-1)), a low detection limit (=0.7 μmol L-1) and a wide quantification range (4-200 μmol L-1). The method was applied to [Cu(H2O)6]2+ determination in two particular LDH-aqueous solution dispersed systems: (1) [Cu(H2O)6]2+ scavenging by etilendiammintetraacetic acid (EDTA) modified Zn-Al-LDHs, and (2) [Cu(H2O)6]2+ release from a copper doped Mg-Al-LDHs. The results obtained are comparable to those reported in previous works using different quantification techniques. FI-AM determination is applied without sample pretreatment (solid-supernatant separation) providing a high sampling rate (above 120 samples h-1) that allows a better comprehension of the processes, particularly at the initial stages.