Flow-injection determination of chromium(III) by its catalysis on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3-methoxyaniline Original Research Article

A flow-injection photometric method was developed for the determination of trace amounts of chromium(III). It is based on its catalytic action on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3-methoxyaniline as a modified Trinder’s reagent to produce an intensely colored dye (λmax=568 nm) in the presence of hydrogen peroxide at pH 7.0–7.3. In this reaction, ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA), diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) and 1,2-dihydroxy-3,5-benzenedisulfonic acid (Tiron) acted as activators for the catalysis of chromium(III); among them EDTA showed the most effective action for the catalysis of chromium(III). Dynamic range was 5–400 ng ml−1 of chromium(III) at a sampling rate of 25 h−1 in the presence of EDTA. The relative standard deviations (R.S.D.) for 40 and 100 ng ml−1 chromium(III) (n=10) were 0.94 and 0.83%, respectively. The chromium(VI) in sample solution can be determined by reducing to chromium(III) by hydrogen peroxide in an acidic medium, which allows total chromium determination. The proposed method was successfully applied to the determination of chromium in certified reference materials of vehicle exhaust particulates (NIES no. 8) and river water (JSAC-0032).