Prior to use, all glassware, bottles and containers were thoroughly cleaned with detergent before being left to soak in 10% nitric acid (HNO3) for 24 h. Finally, the objects were rinsed several times using deionised water. Great care was taken to minimise the risk of contamination throughout the study.
All pH measurements were performed using a Metrohm 744 pH Meter with a combined electrode. The instrument was calibrated prior to each series of measurements using suitable Metrohm buffer solutions.
All the reagents used in this study were of pro analysi quality. Only deionised water was used for dilution and dissolution.