First investigation of polyoxoniobate and polyoxotantalate aqueous speciation by capillary zone electrophoresis

Abstract

Aqueous solutions of hexaniobate (H_xNb₆O₁₉^x−8, 0 ≤ x ≤ 3) and hexatantalate ions (H_xTa₆O₁₉^x−8, 0 ≤ x ≤ 3) have been probed by capillary zone electrophoresis (CE) for the first time. Taking advantage of the UV properties of H_xTa₆O₁₉^x−8 and H_xNb₆O₁₉^x−8, the detection of Nb(V) and Ta(V) could be performed without using toxic or expensive chelating reagents as reported in CE methods previously developed for Nb and Ta samples. The effective electrophoretic mobilities of the hexaniobate and hexatantalate ions were measured as a function of pH in Li⁺, Na⁺ and K⁺-based alkaline media at 25 °C. Although H_xTa₆O₁₉^x−8 and H_xNb₆O₁₉^x−8 have almost identical electronic and structural features, they were easily separated in a wide pH range (9 to 13) using standard bare-fused silica capillary. The separation of Nb and Ta was accomplished in 5 minutes, which affords a promising method for the analytical support of industrial processes. The striking difference observed in the mobilities of H_xTa₆O₁₉^x−8 and H_xNb₆O₁₉^x−8 also led to new insights regarding the ion-association behavior of these highly charged species.