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 i n the presence of thiocyanate was examined. The results showed that N-cinna moyl-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 a bsorptivity of the ternary complex in the organic phase was 4.75 x 10(4). B eer's law was confirmed in the range of 0-16.5 mug/10 ml (organic phase), a nd the sensitivity for log (Io/I) = 0.001 was 0.002 mug cm(-2). Among the 3 6 ions studied, tantalum(V) and titanium(IV) seriously interfered with the determination of niobium(V). The proposed method was successfully applied t o the determination of niobium in steel and stainless steel.