Improved voltammetric method for simultaneous determination of Pt and Rh using second derivative signal transformation - application to environmental samples

The determination of Platinum-group elements (PGE) in relevant environmental matrices is a challenging task. Sensitive and accurate analytical procedures for simultaneous determination of Pt and Rh are still needed. In this study, we report for the first time on the use of second derivative signal transformation to the ultra-trace simultaneous determination of Pt and Rh by Adsorptive Cathodic Stripping Voltammetry (AdCSV). With that step, the ill-defined peaks typically observed in the original voltammograms are transformed into well-shaped peaks, resulting in accurate detection. The experimental conditions were investigated and optimised: a suitable electrolyte for both elements, with less reagents consumption, (0.25 M H2SO4, 0.05 M HCl, 0.01 M FA and 0.5 mM HZ), deposition time (t(d)) and deposition potential (E-d). For t(d) = 120 s and E-d = -0.75 V, linear relationships r > 0.999 were obtained in the concentration range up to 5.8 ng L-1 (27 pM) for Pt and up to 3.4 ng L-1 (34 pM) for Rh. Limits of detection were 0.2 ng L-1 for Pt and 0.08 ng L-1 for Rh. Lower values can be achieved by increasing the deposition time. Limits of quantification, LOQ, calculated as 3 times LOD, were 0.5 ng L-1 for Pt and 0.2 ng L-1 for Rh. The sensitivity of Pt was affected by elevated Zn concentrations, whereas a minor effect was observed for Rh. However, Pt and Rh determinations were not influenced using the standard addition method. Precision as intermediate precision and expressed as relative standard deviation, based on Pt and Rh spiked solutions and digested road dust CRM BCR-723 was 17% and 20% for Pt and Rh, respectively. Recoveries of CRM were around 90% for both elements. The method was successfully applied in the simultaneous determination of Pt and Rh in sediments from Tagus estuary and, for the first time, dissolved Rh was determined in water samples of a waste water treatment plant. Application of this technique in a multidisciplinary approach will be a relevant contribution to the current understanding of PGE cycle and fate in the environment.