Double-wavelength spectrophotometric determination of trace zinc with ZnII-potassium thiocyanate-neutral red system

A new method was developed for determination of trace zinc by double-wavelength spectrophotometry.In the presence of arabic gum,Zn reacts with potassium thiocyanate and neutral red(NR),forming 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 574 nm.The apparent molar absorption coefficient was 5.66×104 L·mol-1·cm-1.The linear range of the determination was 0-1.0 μg/mL,and the limit of detection for zinc was 10.91 μg/L.The method has been applied to the determination of zinc in river water,with the RSDs of 1.7 % and 1.6 %(n= 5) and the recoveries of 99 % and 103 %,respectively.The results agreed well with those obtained by spectrophotometry with dithizone.