Voltammetric method for ultra-trace determination of total mercury and toxic metals in vegetables. Comparison with spectroscopy

A new procedure for the determination of mercury(II), copper(II), lead(II), cadmium(II) and zinc(II) traces in food matrices by square wave anodic stripping voltammetry and standard addition method is proposed. A rapid, inexpensive and multi-analyte analytical method suitable for food safety control is provided. Comestible vegetables were chosen as samples. A two-step, sequential determination was defined, employing two working electrodes: a gold electrode (GE) for mercury(II) and copper(II), and subsequently a hanging mercury drop electrode (HMDE) for copper(II), lead(II), cadmium(II) and zinc(II). No sample pre-treatment was needed. Spinach leaves, tomato leaves and apple leaves were employed as standard reference materials to optimize and defined the analytical procedure. The new method shows good selectivity, sensitivity, detectability and accuracy. A critical comparison with spectroscopic measurements is discussed. Spinach, lettuce and tomato samples sold on the market were analysed as real samples. Lead(II) and cadmium(II) concentration exceeded the relevant legal limits.