Updated investigation of the reaction between copper and naphthol blue black B and determination of trace amounts of copper in water

The biological dye, naphthol blue black B (NBBB) was found to produce a sen sitive reaction with copper(II) at pH over 7. This reaction was very intere sting. The complexation of Cu(II) with NBBB happened at pH between 6 and 11 but the redox catalytic reaction happened at pH over 11, where copper(II) served as a catalyst. In this study, ordinary spectrophotometry was limited for use because of the serious interference of excess reactant. A new meth od, beta-correction principle, was applied because it can eliminate the abo ve interference. This method can give the simple determination of propertie s of Cu-NBBB complex solution at pH 9.5, which involved the complex ratio, real molar absorptivity, and stability constant (K). Results showed that th e formed Cu-NBBB complex occurred as Cu(NBBB) at pH 9.5, its real rather th an apparent absorptivity was equal to 7.62 x 10(3) L mol(-1) cm(-1) at 630 nm, and its stability constant was 1.32 x 10(6). The redox catalytic reacti on between Cu(II) and NBBB at pH 13 was used to determine trace amounts of copper in water. This reaction was very sensitive and highly selective. Mos t of the metals did not interfere with the direct determination of copper. The detection limit of copper was 0.002 mg/L, and the recovery was between 90 and 104% with the relative standard deviation of less than 11%.