Photometric Determination of Trace Amount of Lead in Pure Zinc with Polybromo-Phenylfluorone

The color reaction between a polybromo-phenylfluorone chromagenic reagent, 3′,5′-dibromo-4′-hydroxy-4,5-dibromophenylfluorone (DBHDBPF), and Pb(Ⅱ) was studied. In a Na2B4O7-NaOH buffer solution of pH 10.0, and in the CTMAB microemulsion, a stable coordination complex with the molar ratio (DBHDBPF∶Pb) of 2 to 1, was formed, with its absorption maximum at the wavelength of 592 nm. Value of apparent molar absorptivity was found to be 1.58×105L·mol-1·cm-1. Based on these facts, a method of spectrophotometry for the determination of lead in pure zinc was proposed using 4-methyl-2-pentanone (MIBK) to extract Pb(Ⅱ) from sample solution. Beer′s law was held in the range within 1.8 mg·L-1, with detection limit (3S/N) of 0.12 mg ·L-1. The proposed method was applied to the determination of Pb in CRM′s of pure zinc (GBW 02701 and GBW 02702), giving results in consistency with the certified values.