Application of ion-exchanger phase photoacoustic spectroscopy to flow analysis of trace amounts of iron in water

Ion-exchanger phase photoacoustic spectroscopy has been applied to the flow analysis of trace amounts of iron in water. The reaction product of iron(II) with 4,7-diphenyl-1,10-phenanthroline-disulphonate, introduced into a carrier solution stream in the flow system, was concentrated on a small amount of QAE-Sephadex gel settled in a fused silica glass tube (1.5 mm i.d.) of a photoacoustic cell. The photoacoustic signal produced by pulsed laser irradiation of the gel beads at 532 nm was detected by a cylindrical piezoelectric transducer which was attached outside the glass tube. When 3.7 ml of a sample solution was introduced into the flow system, the sensitivity of this method was 590 times higher than that of the corresponding solution photoacoustic spectrometry and the detection limit of iron was 0.33 ng/ml. Because the coloured complex was desorbed from the cell with a desorbing agent solution, the present method could afford repeated analyses of natural water samples containing iron at ng/ml levels without any preconcentration procedures.