Improving precision and trueness in the quantification of cadmium using square wave anodic stripping voltammetry and bismuth film electrodes

Abstract

Single-point standard addition, along with internal standard calibration (SSA-IS), is investigated as a new protocol in cadmium quantification by square wave anodic stripping voltammetry (SWASV) and using bismuth film/glassy carbon electrode (Bi/GCE). The bismuth oxidation signal used as an in situ internal standard compensates for random variations between measurements. Moreover, the SSA-IS calibration method is proposed as a practical solution to the passivation of the working electrode. SSA-IS improves the results (RSD = 6.77 %, bias = 5.16 %), compared to the multi-point external standard calibration without internal standard (ESC), (RSD = 29.71 %, bias = 58.80 %) and with internal standard (ESC-IS), (RSD = 6.88 %, bias = 29.23 %). Also, the uncertainty and trueness of the proposed method were estimated and compared with the NIST 3108 reference material. An average concentration of 9.77 ± 0.96 mg g−1 was obtained, which statistically agrees with the certified value of the NIST reference material, 10.007 ± 0.027 mg g−1. Using the SSA-IS method improves the metrological qualities of the analytical technique, making the methodology ready to be tested in real samples such as cocoa.