A simple and relatively fast method for the selective separation and preconcentration of trace amounts of copper in real samples, for determination by flame atomic absorption spectrometry is reported. By passing the aqueous solutions of 5 through an octadecyl-bonded silica membrane disk modified by N-benzoyl N-phenyl hydroxyl amine (BPHA). copper is retained quantitatively while almost all matrix elements are passed through. The retained copper ions are then eluted from the disk by minimal amount of HNO3. Maximum capacity of the disk modified by 5 mg BPHA is found to be 217 +/- 6 mu g of Cu2+ ions. The method permitted separation of copper ions from coexisting metal ions with an enrichment factor of 200. A good precision for 10 mu g L-1 copper (2.5% R.S.D. n = 8) and detection limit (3S(b) m(-1)) 0.3 mu g L-1 are obtained. The accuracy is assessed by analysis of two standard reference materials (NBS-364) and (JSS-651-7). The proposed method is applied to the determination of copper in water, waste water and steel samples.