Determination of zinc in electroplating wastewater by double-wavelength spectrophotometry

A new method for determination of trace zinc by double-wavelength spectrophotometry was developed using 462 nm and 575 nm as the detection wavelength.In presence of arabic gum,Zn(Ⅱ) reacts with potassium thiocyanate and neutral red(NR) to form a stable ion-association complex 4[Zn(SCN)6] in HAc-NaAc buffer solution at pH 5.7,which leads to the fading of NR.As a result,there were a positive absorption peak at 462 nm and a negative absorption peak at 575 nm.The results showed that Beer′s law was obeyed in range of 0.0～1.0 μg/mL for zinc,and its apparent molar absorptivity of 5.67×104 L·mol-1·cm-1.when this method was applied to the determination of trace zinc in electroplating wastewater,the results were in good agreement with those provided by 5-Br-DMPAP spetrophotometric method.The relative standard deviation was less than 4% and the recoveries of samples were between 98.0% and 102.5%.