Electrochemical Determination of the Fe(III)/Fe(II) Ratio in Archaeological Ceramic Materials Using Carbon Paste and Composite Electrodes

Abstract

A method for determining the iron(III)/iron(II) ratio in ceramic materials based on microsample attachment to graphite/polyester composite electrodes is presented. This quotient is of considerable interest for determining the nature and firing conditions of the original materials in archaeological ceramics. The electrochemistry of iron in ceramic materials in acetic/acetate and Na2EDTA aqueous solutions is described in terms of reductive dissolution processes of iron(III) materials and oxidative dissolution processes of iron(II) ones. The iron(III)/iron(II) ratio is determined from peak area measurements in linear scan voltammograms performed in 0.10 M acetic/acetate buffer (pH 4.70) and 0.10 M Na2EDTA solutions. A second semiempirical method based on peak current measurements in repetitive cyclic voltammetry is also described. Both procedures were satisfactorily tested using a set of certified clays and applied to the study of a series of ceramic samples from Manises (Spain), dated on XVth and XVIIth–XVIIIth centuries. Results in agreement with SEM and XRD data are obtained.