Suitability of the voltammetry of immobilized microparticles to detect and discriminate lead compounds in microsamples of ancient black cosmetics

Lead compounds, in the form of galena, have been used as eye cosmetics since ancient times and they still appear in traditional products. The presence of some black pigments in several archaeological glass objects gave us the opportunity to study the nature of these products, in order to evaluate the results of an electrochemical method to characterise lead compounds when only heterogeneous microsamples are available and the material requires to be as less manipulated as possible. The present paper describes the data obtained with an electroanalytical methodology (Voltammetry of immobilised microparticles, VMP), and a complementary Scanning Electron Microscopy study, to detect these lead compounds. A simple and fast characterisation method is discussed in order to be able to monitor the presence of lead compounds without previous sample preparation, directly in the solid micro-sample, and using an affordable instrumentation. PbS could be identified and distinguished from other lead compounds in cosmetics by Differential Pulse VMP in 1 M NaCl medium by a set of three peaks (−0.63 V, −0.44 V, +0.45 V) in the anodic voltammogram and two peaks around −0.65 V and +0.45 V in the cathodic scan. The results showed the suitability of the electroanalytical method, offering valuable information about the chemical and mineral composition of the samples using a minimum amount of material, and illustrating the advantages in terms of time consuming, cost and accessibility of the laboratory facilities