Determination of Micro Zinc( II ) in Electroplating Wastewater by Highly Sensitive Coloring Spectrophotometry

Based on the fact that sensitive coloring reaction takes place between Rhodamine B( RhB) and zinc( II) in HCl solution containing potassium rhodanate( KSCN) and polyethylene glycol( PEG),a highly sensitive coloring spectrophotometric method was established to determine micro zinc( II) in electroplating wastewater. Results showed that Zn( II) reacted with KSCN and RhB to form a stable ternary complex Zn( SCN) 4( RhB) 2 with a molar ratio of 1 ∶ 4 ∶ 2 as well as a maximum absorption wavelength of 600 nm and an apparent molar absorption coefficient of 1. 65 × 106L /( mol · cm),while Beer 's law was obeyed in zinc(Ⅱ) concentration range of 0 ~ 0. 060 mg / L. Moreover,the content of micro zinc( Ⅱ) in electroplating wastewater determined by the present method agreed well with that determined by 5-Br DMPAP spetrophotometric method; namely,the relative standard deviation of six cycle measurements was below 4%,and the labeled recoveries of samples were in the range of 96. 5% ~ 102. 0%.