Ammonium retention by Amberlite IRC-748 resin: useful for concentration assessments

Chelating ion exchange resins are widely used to eliminate metal interferences in the analysis of ammonium (NH ₄ ⁺ ) in soil extraction solutions. However, their potential to co-adsorb NH ₄ ⁺ remains underexplored. Here, synthetic metal ion solutions containing 6–30 mg L ^-1 NH ₄ ⁺ and the metal cations Ca ²⁺ , Mg ²⁺ , Cu ²⁺ , Mn ²⁺ , and Zn ²⁺ were treated with Amberlite IRC-748 resin. The resin efficiently removed Ca ²⁺ (−42.2%), Mg ²⁺ (−21.1%), Cu ²⁺ (−99.9%), Mn ²⁺ (−56.9%), and Zn ²⁺ (−93.6%). However, NH ₄ ⁺ losses of 2.2–5.6% were observed, indicating concentration-dependent co-adsorption. While these losses may be acceptable for concentration measurements via routine assays such as photometric analysis, they may still affect the accuracy of high-precision N analyses that rely on quantitative NH ₄ ⁺ recovery. This highlights a methodological caveat for resin-treated samples, especially in low-NH ₄ ⁺ environments. We therefore recommend including recovery assessments and correction factors when using chelating resins to improve accuracy in NH ₄ ⁺ quantification.