There is currently considerable interest in the determination of heavy metals for speciation in naturalwater samples. It is necessary to study the migration of trace iron(II) in river-water. In our previous studies, photoacoustic spectrometry (PAS) was used to determine the phosphate ion as a Molybdenum-Blue species adsorbed on uniform anion-exchange beads. 1 We made a compact PAS apparatus combined with a diode laser head (wavelength 826 nm) as a radiation source and a highly sensitive microphone for the photoacoustic cell. Hence, PAS was applied to the determination of trace iron(II) in natural-water samples.Highly sensitive and selective spectrophotometric methods for water-soluble iron(II)-complex ions have been reported. [3][4][5][6][7][8][9] There are some reagents having a maximum absorption wavelength in the range of nearinfrared rays; for example, 2-nitroso-5-[ethyl-N-(3-sulfopropyl)amino]phenol (Nitroso-ESAP) (752 nm) 5 , 2-nitroso-5-(N-propyl-N-sulfopropylamino)phenol (Nitroso-PSAP) (756 nm) 5 and 2-(5-nitroso-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (Nitroso-PAPS) (793 nm). 8 Nitroso-PSAP was chosen for use in subsequent studies, because the pH range for the formation of the iron(II)-complex anion is wide.On the other hand, Ohzeki et al. 10 proposed a preconcentration technique based on the adsorption of trace amounts of copper as complexes with various chelating agents using finely pulverised anion-and cationexchange resins of the macroreticular type. In our previous studies 11,12 , this preconcentration technique was applied to the determination of ng l -1 levels of gallium in mine-drainage and river-water samples by electrothermal atomic absorption spectrometry.In the present study, the authors developed a new sensitive method by PAS for ng l -1 levels of iron(II) in water samples, based on the preconcentration of a membrane filter with a pulverized anion-exchange resin.It has become very important to determine trace amounts of iron(II) in situ in environmental samples, especially in natural water. The proposed method was applied to a visual method 13 for the determination of the total iron; it has wide determination range (0.05 -2.0 mg). Experimental ApparatusThe samples were analyzed on a photoacoustic spectromeric system: 2 a 30-mW diode laser head (Melles Griot 06 DLL 507, wavelength of 826 nm); diode laser drivers equipped with a thermoelectric cooler control (Melles Griot 06 DLD 003); oscillator (Kenwood FG-273); auto-phase lock-in amplifier (NF LI-574); recorder (Tohshin TO 2H1-H); microphone (National WM-612); photoacoustic cell made of brass (sample chamber, 13 mm in diameter). To collect the finely 333 ANALYTICAL SCIENCES APRIL 1998, VOL. 14 1998 © The Japan Society for Analytical Chemistry Photoacoustic Spectrometric Determination of Trace Iron(II) after Preconcentration on a Membrane Filter with a Finely Pulverized Anion-Exchange ResinJunichi SHIDA † and Isamu MASUDA Department of Materials Science and Engineering, Faculty of Engineering, Yamagata University, Yonezawa 992, J...