A Robust Cost-Effective Spectrophotometric Method for Nb Determination in Refractory Nb-doped Gadolinium Zirconate:...

A simple, robust and cost-effective analytical methodology was developed for the determination of niobium in highly refractory materials: Nb-doped gadolinium zirconate (Gd₂Zr₂O₇:Nb) and niobium pentoxide (Nb₂O₅). The challenge of digesting these matrices was successfully accomplished by establishing two independent dissolution procedures: (i) Fluoride-free digestion under reflux conditions and (ii) microwave-assisted digestion using a minimal volume of hydrofluoric acid (0.1 mL of 40% hydrofluoric acid). This dual digestion approach provides reliability, flexibility and robustness to the method. Subsequent to dissolution of highly refractory solid matrices, a one-step spectrophotometric method for Nb determination based on the formation of peroxoniobium complex in sulfuric acid medium was optimised and developed. The proposed method is easy and straightforward, with fewer procedural steps and requires a lower chemical inventory. The developed method has a wide linear dynamic range of 2-225 ppm Nb spanning two orders of magnitude with a regression coefficient of 0.99945 and a detection limit of 0.4 ppm. The precision obtained is 2.13% (method relative standard deviation [RSD], n = 5) and 0.17% (instrumental RSD, n = 9). The recovery of Nb from spiked samples at a 50 ppm level is greater than 98% and, thereby validating the proposed method. Furthermore, the proposed method is independently authenticated using total reflection X-ray fluorescence/energy-dispersive X-ray fluorescence techniques, with the results showing good agreement within the 95% confidence interval.