<p>A sensitive and selective ion chromatography (IC) method combined with on-line enrichment technology was developed for the determination of trace zinc ions (Zn²⁺) in the primary coolant of nuclear reactors. This method enables selective large-volume enrichment of Zn²⁺, overcoming interferences from high-concentration boric acid (&gt;2000 mg/L) and lithium (3 mg/L) matrices. A 2.5 mM methanesulfonic acid—0.8 mM oxalic acid elution system was used in conjunction with direct conductivity detection. Under optimized conditions, the standard curve exhibited a linear relationship (R² &gt; 0.999) within the Zn²⁺ concentration range of 10–100 μg/L. The boric acid concentration in the coolant matrix showed no interference with Zn²⁺ testing, while lithium hydroxide caused retention time shifts of Zn²⁺, which were eliminated by a matrix matching strategy. The spiked recovery of 15&#xa0;μg/L in simulated samples was 99.47% (n=7, RSD=0.89%), and the method detection limit was 0.41&#xa0;μg/L. This approach provides a robust and cost-effective solution for real-time monitoring of Zn²⁺ in nuclear coolants, contributing to corrosion control and radiation field optimization in nuclear power plants.</p>