Spectrophotometric determination of niobium(V) with N-cinnamoyl-N-2,3-xylylhydroxylamine and thiocyanate

The colour reaction of niobium(V) with the four kinds of hydroxamic acids in the presence of thiocyanate was examined. The results showed that N-cinnamoyl-N-2,3-xylyl-hydroxylamine (CXHA) was the most suitable reagent for the spectrophotometric determination of small amounts of niobium. CXHA reacts with niobium in the presence of thiocyanate to form an extractable ternary complex into carbon tetrachloride from 4-7 M hydrochloric acid. The molar absorptivity of the ternary complex in the organic phase was 4.75 x 10(4). Beer's law was confirmed in the range of 0-16.5 mug/10 ml (organic phase), and the sensitivity for log (Io/I) = 0.001 was 0.002 mug cm(-2). Among the 36 ions studied, tantalum(V) and titanium(IV) seriously interfered with the determination of niobium(V). The proposed method was successfully applied to the determination of niobium in steel and stainless steel.