Determination of cadmium after preconcentration with the ion pair of 2-(bromo-2-pyridylazo)-5-diethylaminophenol and tetraphenylborate on microcrystalline naphthalene

Cadmium can be preconcentrated from a large volume of its aqueous samples in the pH range 4.0 . 7.0 as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) ammonium tetraphenylborate ion associated complex on microcrystalline naphthalene or by adsorbing cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) cationic complex on the adsorbent ammonium tetraphenylborate naphthalene filled in a column. After the preconcentration step, the solid mass consisting of cadmium complex and naphthalene is dissolved with 5 mi of dimethylformamide and the metal determined by atomic absorption spectrometry. The calibration graph is linear over the concentration range 1.5-125 mug of cadmium in 5 mi of the fnal dimethyl-formamide (DMF) solution. Eight replicate determinations of 25 mug of cadmium give a mean absorbance of 0.136 with a relative standard deviation of 1.48% for pure solutions and 2.2% for complex samples respectively. The sensitivity fur 1% absorption is 0.162 mug ml(-1) in the present case while it is 0.135 mug ml(-1) for aqueous sample with this instrument, which is two times better than the aqueous samples, at the same time the preconcentration factor is 80. The interference of a large number of anions and cations on the determination of cadmium has been studied and the optimized conditions developed have been utilized for its trace determination in various standard alloys, biological and environmental samples.