Detecção de zinco em fertilizantes de Estruvita por voltametria de redissolução anódica de onda quadrada utilizando um eletrodo de ouro descartável

Abstract

Struvite is a natural fertilizer that can be manufactured (via precipitation) from urine by adding magnesium oxide (MgO). This compound can present in its composition large amounts of macro and micronutrients. However, toxic substances (including metals) present in the urine can be concomitantly precipitated with macros and micronutrients and contaminate the soil, plants, water, and animals. In this sense, the present work shows a simple, sensitive and low-cost electroanalytical method for the determination of zinc in struvite by square wave anodic stripping voltammetry (SWASV) using gold screen- printed electrodes (SPGE) coupled to a 10 mL electrochemical cell. Under optimized conditions, the proposed method had a low detection limit and a wide linear range of 2.55 μg L-1 (99.7% confidence level), 10 to 70 μg L-1, respectively. Relative standard deviation (RSD) and inter-electrode deviation were estimated at 3% (n = 10, 20 μg L-1) and 16% (n = 3), respectively. To obtain these values, the following parameters were used: -0.9 V and 90 s for the potential and time of pre-concentration, respectively; 1000 rpm for stirring rate; 4 mV for step potential; 50 mV for modulation amplitude and 50 Hz for frequency using Britton-Robinson buffer (BR) 0.04 mol L-1 at pH 7.0 as the supporting electrolyte. In addition, the technique employed allowed a quantification limit of 8.4 μg L-1 and presented satisfactory recovery values of 98% ± 1%, indicating that it is a precise and accurate direct analysis methodology with rapid responses, without influences of interferents, of low cost and that makes possible in-field analysis.