Effects of common metal ions on the determination of anions by suppressed ion chromatography

The effects of common metal ions (Na+, K+, Ca2+, Mg2+, Al3+ and Fe3+) on the determination of nitrate, phosphate and sulfate by suppressed ion chromatography were investigated. The responses of nitrate within 1–10 mg/l were not affected in the presence of six metal ions at 10 mg/l. The peak areas of 1.0 mg/l sulfate increased significantly at 10 mg/l Fe3+ or Al3+ up to 51.34 and 48.37%, respectively. In the presence of 10 mg/l Fe3+, the peak area of 1 mg/l and 10 mg/l phosphates decreased by 91.44 and 33.71%, respectively. At 10 mg/l Al3+ the peak areas of phosphate also increased slightly. The adverse effect of Fe3+ on the determination of phosphate could be overcome effectively by reducing the pH of the samples. The method to overcome the adverse effect was studied.