A robust gradient chromatographic separation of N.C.A. ¹⁷⁷Lu from irradiated ^natYb target using a DEHPA-impregnated Amberlite resin

No-carrier-added (N.C.A.) ¹⁷⁷Lu is one of the most promising radionuclides for targeted β⁻ therapy; however, its separation and purification from irradiated ytterbium remain challenging due to the close chemical similarity of Lu and Yb. In this work, Amberlite IR120H resin impregnated with di-(2-ethylhexyl) phosphoric acid (DEHPA) was developed and comprehensively characterized. The resulting material was subsequently applied as a selective separation stationary phase. Batch uptake experiments were conducted over a range of pH values to evaluate the extraction behavior of Lu(III) and Yb(III). Quantitative uptake of both cations was achieved at pH 4.5, where limited Lu/Yb selectivity was observed. Chromatographic trials revealed that isocratic α-HIBA eluents provided only partial resolution, limiting radiochemical purity to ∼91%. By contrast, a stepwise gradient of α-HIBA (0.05-0.20 M; pH 4.5-5.0) yielded a sharp and distinct Lu fraction, achieving 88% recovery and radiochemical purity of 96%, while suppressing Yb breakthrough. Quality control assays confirmed radionuclidic purity above 99.9% and sub-ppm Yb contamination. These results establish a simple and robust route for producing therapeutic-grade N.C.A. ¹⁷⁷Lu suitable for clinical applications.