A new concentration on-line system for Zn(II), Cu(II), Pb(II) and Cd(II) determination was developed. The method is based on the adsorption of metals on the inner surface of glass capillary tubes. The metal ions that were concentrated on a glass surface for 5 minutes were eluted on-line with a small amount of dilute nitric acid solution in the carrier line. The flow system was composed of four channels, including the carrier, sample solution, buffer solution and detection reagent. The concentration efficiencies of Zn(II), Cu(II), Pb(II) and Cd(II) obtained by the present method were about 166, 143, 394 and 102 times, respectively. Further, the eluted metal ions were then determined with 4-(2-pyridylazo)resorcinol (PAR) by spectrophotometry. The optimum conditions by the present method were as follows: buffer solution, pH 9.0(Zn), pH 9.0(Cu), pH 8.5(Pb), pH 9.5(Cd); PAR, 4.0×10
−4 M, pH 10; eluent HNO
3, 3.0×10
−2 M 20 μl; R.C. length, 1.0 m(Zn), 0.1 m(Cu), 1.0 m(Pb), 0.2 m(Cd); wavelength: 493 nm(Zn), 517 nm(Cu), 520 nm(Pb), 504 nm(Cd). The detection limits of Zn(II), Cu(II), Pb(II) and Cd(II) were 0.076 ppb, 0.12 ppb, 0.69 ppb and 0.25 ppb, respectively. The sensitivities of Zn(II), Pb(II) and Cd(II) obtained by the present method were superior to that of the Teflon-tube method as a conventional method. The present method was successfully applied to the determination of trace Zn(II) in tap water after masking Cu(II) and Fe(II) with sodium thiosulfate, Cd(II) with potassium iodide, and Mn(II) with triethanolamine, respectively.
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