Flow-injection analysis of copper(II) with PAR in the presence of EDTA.

(II) is spectrophotometrically determined with 4-(2-pyridylazo)resorcinol (PAR) 1–4 in the presence of EDTA. This color reaction can never be carried out by a batch method because the stability constant of copper(II)-EDTA (log K = 18.8) is larger than that of copper(II)-PAR (log K = 14.8). 1 Therefore, PAR is used as an indicator in the EDTA titration of copper(II). We found that a color reaction of copper(II) with PAR occurred in the presence of EDTA, the absorption based on the complexation of copper(II) with PAR was detectable by spectrophotometry and the obtained signals corresponded to the copper(II) contents, if flow-injection analysis (FIA) was adopted. The subsequent ligand-exchange reaction of copper(II)-PAR to copper(II)-EDTA occurred after passing through a flow-through cell. Consequently, the free PAR was regenerated and could be reused repeatedly. This makes it possible to adopt the circulatory flow-injection method (cyclic FIA) 5–10 and to determine copper(II), repetitively. There is a need for a simple, fast, selective and automated method to monitor or determine metal ions. Compared to conventional batch methods and chromatography, FIA offers many significant advantages when the concentration of one analyte has to be determined. The aim of this study was to reveal the color reaction of metal ions with an organic reagent in the presence of a complexing agent (EDTA) and to develop a cyclic FIA for the repetitive determination of metal ions. A famous spectrophotometric reagent, PAR, was chosen because of its water solubility compared to that of, 1-(2-pyridylazo)-2-naphthol (PAN), 1–4 and the copper(II)-PAR-EDTA system has been employed as a model for a cyclic FIA. The proposed method allows as many as 100 repetitive determinations of 2.5 ppm copper(II) with only a 100 ml reservoir solution. The use of a cyclic FIA provides a better utilization of the reagents, while minimizing the waste, decreasing the operating cost and shortening the determination time. This is one approach to the ZERI (zero emissions research initiative) concept. Experimental Chemicals and apparatus All chemicals were of analytical-reagent grade. A standard copper(II) solution (1000 ppm) and PAR were purchased from Wako Pure Chemical Co. The water used for preparing solutions was obtained by a Milli-Q water-purification system. A schematic diagram of the cyclic FIA used in this work is shown in Fig. 1. The FIA apparatus consisted of a double plunger pump (Flom 201), a 6-way rotary valve (Rheodyne 9725, 10 µl loop), a visible spectrophotometer (Soma S-3250) equipped with …