用双波长缔合光度法测定镀锌废水中的微量Zn^(2+)

Determination of Traces of Zn^(2+) in Zinc Electroplating Wastewater by Double-Wavelength Spectrophotometry

在阿拉伯树胶存在下,在pH=5.5的NH4Ac-HAc缓冲溶液中,Zn2+与硫氰化钾和中性红(NR)反应生成稳定的离子缔合物[NR]4[Zn(SCN)6],使NR褪色,在462 nm处出现正吸收峰,575 nm处出现负吸收峰。选定测定波长为462 nm和575 nm,建立了一种测定微量Zn2+的新的双波长光度法。结果表明:锌含量在0～1.0μg/mL内符合比尔定律,表观摩尔吸光系数为5.72×104L/(mol.cm),本方法用于测定镀锌废水中微量Zn2+,结果与5-Br-DMPAP光度法相符,6次测定值的相对标准偏差小于4%,加标回收率为98.7%～101.8%。

In the presence of arabic gum,Zn2-reacts with potassium thiocyanate and neutral red(NR) to form a stable ion-association complex [NR]4 [Zn(SCN)6] in the buffer solution of NH4Ac-HAc with a pH value of 5.5,leading to the fading of NR in association with emerge of a positive absorption peak at 462 nm and a negative absorption peak at 575 nm.Thus a new double-wavelength spectrophotometric method was established to determine traces of Zn2+ in the wastewater of zinc electroplating by setting detection wavelength as 462 nm and 575 nm.It was found that Beer's law was obeyed in a range of 0～1.0 μg/mL for Zn2+ concentration,and the apparent molar absorptivity was 5.72×104 L/(mol·cm).When the method was adopted to determine traces of Zn2+ in zinc electroplating wastewater,results were in good agreement with those obtained by 5-Br-DMPAP spetrophotometric method,with a relative standard deviation of less than 4 % and a recovery of 98.7 %～101.8 %.