Mineral water and isotonic sports drinks (hydroelectrolytic supplement) are sources of electrolytes, and one among them is zinc, an important microelement for several functions of the body. In this study, a novel on-line preconcentration analytical method was developed and validated using atomic fluorescence spectrometry and chemical vapor generation to determine Zn, in mineral water and isotonic sports drinks employing multivariate optimization. The optimal parameters for the system were: pH = 8.00; [Na₂CO₃] = 6.5 × 10⁻³ mol L⁻¹; sample flow = 5.70 mL min⁻¹; flow rate = 8.00 mL min⁻¹; and the elution flow rate was adjusted to 2.40 mL min⁻¹ to obtain the analytical speed. The method to determine zinc in samples showed adequate linearity, repeatability and accuracy. The limits of detection (LOD) and quantification (LOQ) obtained for zinc were 0.03 and 0.09 μg L⁻¹, respectively. Zinc concentration in mineral water and isotonic sports drinks ranged from 29.00 to 78.59 μg L⁻¹. The enrichment factor (88.92) and sampling frequency/samples per hour (51) were obtained. Therefore, the results showed that the developed method is simple, fast, reliable, sensitive and selective for the determination of zinc in mineral water and isotonic sports drinks and can be applied in the control of the chemical and toxicological quality of these foods. Furthermore, the multivariate methodology using the complete factorial design and the Box–Behnken design was adequate for the optimization of the preconcentration system variables that influence the generation of the analytical signal.