Flow injection spectrophotometry of lead(II) by on-line preconcentration method using silica capillary tube

A novel concentration on-line system for Pb(II) determination has been developed. The method is based on the adsorption of Pb(II) ions on the inner surface of a silica capillary tube (length, 25 m; i.d., 0.53 mm). The metal ions that were concentrated on a silica surface for 180 minutes were eluted on-line with a small amount of diluted nitric acid solution in a carrier line. The flow injection analysis system was composed of four channels, including the carrier, sample, buffer and detection reagent solution. The concentration efficiency of Pb(II), obtained by the present method, was about 910. The eluted Pb(II) ion was then determined with tetraphenylporphinetetrasulfonic acid (TPPS) by spectrophotometry. The calibration curve was linear at over the range of 0 to 2.5 ppb. The optimum conditions by the present method were as follows: pH of buffer solution for concentration, 9.5; TPPS, 5.0 x 10(-5) M, pH of TPPS solution, 12; concentration of eluent HNO3, 5.0 x 10(-3) M; volume of the eluent, 10 mu l; reaction coil length, 3.5 m; wave-length, 464 nm. The detection limits of Pb(II) was 0.004 ppb. The RSD of 1.5 ppb Pb(II) was 1.4% (n = 5). The present method was successfully applied to the determination of trace Pb(II) in river, swamp and tap water samples after masking Fe(III) and Cu(III) with triethanolamine.