Catalytic flow injection determination of vanadium by oxidation of N-(3-sulfopropyl)-3,3',5,5'-tetramethylbenzidine using bromate.

A catalytic flow-injection (FI) method was developed for the determination of 10(-9) mol l(-1) levels of vanadium(IV, V). The method is based on the catalytic effect of vanadium(V) on oxidation of N-(3-sulfopropyl)-3,3',5,5'-tetramethylbenzidine (TMBZ.PS) using bromate as oxidant to form a yellow dye (lambda(max)=460 nm). The use of 5-sulfosalicylic acid (SSA) as an activator enhanced the sensitivity of the method. The calibration graphs with a working range 0.05-8.0 ng ml(-1) were obtained for vanadium(V). Vanadium(IV) was also determined, being oxidized by bromate. The detection limit (signal/noise, S/N=3) was 0.01 ng ml(-1) (ca. 2x10(-10) mol l(-1)) vanadium. The relative standard deviations (R.S.D.) for 15 determinations of 0.5 ng ml(-1) vanadium, and for ten determinations of 0.1 and 1.0 ng ml(-1) vanadium were 0.41, 2.6 and 0.25%, respectively, with a sampling rate of 15 samples h(-1). The proposed method was successfully applied to the determination of vanadium in natural waters.