A 1000 mg Zn standard solution was prepared from Zn metal (Aldrich, 99.99%) dissolved in hydrochloric acid 1 + 1
(v + v).
A 1000 mg L1 Fe standard solution was prepared from Mohr is salt (ferrous ammonium sulphate hexahydrate, Baker).
All other reagents were of analytical reagent grade.
All glassware was soaked overnight in 10% (v/v) nitric acid and then rinsed with ultrapure water.