Solid phase preconcentration of iron as methylthymol blue complex on naphthalene-tetraoctylammonium bromide adsorbent with subsequent flame atomic absorption determination

A sensitive and selective preconcentration method for the determination of trace amounts of iron by atomic absorption spectrometry has been developed. Iron forms a complex with methylthymol blue at pH=3. This complex is retained by naphthalene tetraoctylammonium bromide adsorbent in a column with a height of about 2 cm. The adsorbed metal complex is then eluted from the column with nitric acid and its iron content is determined by flame atomic absorption spectrometry (FAAS). The effect of different variables such as pH, reagent concentration, flow rate and interfering ions on the recovery of the analyte was investigated. The calibration graph was linear in the range 25–350 ng ml−1 of iron in the initial solution with r=0.9994. The limit of detection based on 3Sb criterion was 12 ng ml−1 and the relative standard deviation for eight replicate measurements of 150 and 300 ng ml−1 of iron was 3.1 and 1.8%, respectively. This procedure was successfully applied to the determination of iron in tap and sewage water samples.