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 i n the pH range 4.0 . 7.0 as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) ammonium tetraphenylborate ion associated complex on mi crocrystalline naphthalene or by adsorbing cadmium-2-(5-bromo-2-pyridylazo) -5-diethylaminophenol (5-Br-PADAP) cationic complex on the adsorbent ammoni um tetraphenylborate naphthalene filled in a column. After the preconcentra tion 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 concentr ation 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 m ean absorbance of 0.136 with a relative standard deviation of 1.48% for pur e 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 8 0. The interference of a large number of anions and cations on the determin ation of cadmium has been studied and the optimized conditions developed ha ve been utilized for its trace determination in various standard alloys, bi ological and environmental samples.