Use of heteroligand complexes in analytical chemistry of niobium and tantalum

A review of modern precise spectrophotometric and extraction-spectrophotometric methods for analyzing Nb and Ta is presented. These methods are based on the use of multi-ligand (trinary, quaternary, mixed) complexes of these elements with organic reagents. To develop extraction-photometric methods for quantitative analysis of Ta in the presence of Nb use is made of complexes which these elements form with polyphenols, azo compounds, metallochromic indicators and heteropolyacids. The extraction-photometric methods are based on the use of multi-ligand complexes of the ionic association type. Owing to this the volumetric and gravimetric methods can be used here. The research on multi-ligand complexes of Nb and Ta with a number of reagents provides a basis for developing precise analytical methods for determining Nb and Ta in different materials and in the presence of many other elements without their separation