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 (NH4+) in soil extraction solutions. However, their potential to retain NH4+ remains underexplored. Here, synthetic metal ion solutions containing 6–30 mg L−1 NH4+ and the metal cations calcium (Ca2+), magnesium (Mg2+), copper (Cu2+), manganese (Mn2+), and zinc (Zn2+) were treated with Amberlite IRC-748 resin. The resin efficiently removed Ca2+ (−42.2%), Mg2+ (−21.1%), Cu2+ (−99.9%), Mn2+ (−56.9%), and Zn2+ (−93.6%). However, NH4+ losses of 2.2–5.6% were observed, indicating concentration-dependent NH4+ retention by the resin. While these losses may be acceptable for concentration measurements via routine assays such as photometric analysis, they may affect the accuracy of high-precision N analyses that rely on quantitative NH4+ recovery. This highlights a methodological caveat for resin-treated samples, especially in low-NH4+ environments. Recovery assessments and correction factors are therefore recommended when using chelating resins to improve the accuracy of NH4+ quantification.