Design of a Flow-Through Voltammetric Sensor Based on an Antimony-Modified Silver Electrode for Determining Lithol Rubine B in Cosmetics

Lithol Rubine B (LRB; the disodium salt of 3-hydroxy-4-[(4-methyl-2-sulfophenyl) azo]-2-naphthalenecarboxylic acid) was detected using high-performance liquid chromatography with an electrochemical (antimony film on silver) detector (HPLC-ECD). For direct current (DC) mode, with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.125 to 1.80 μg/mL was found. The detection limit of our method was approximately 2.0 ng/mL. An antimony-modified silver detector was used to demonstrate that LRB is electrochemically reduced in acidic media and to analyze commercial cosmetics to determine their LRB content. Findings using HPLC-ECD and HPLC with an ultraviolet detector were comparable.