Finally, the filtrates were analysed for copper using atomic absorption spectrometry and a GBC Avanta R flame atomic absorption spectrometer. Each determination was obtained by taking the average of three replicate measurements. More than 90% of the determinations had a relative standard deviation of less than 2%, and only those with a relative standard deviation less than 2.5% were included in the reported results. The calibration curve was based on four standards ranging from 0.500 to 10.00 mg/l. Prior to analysis, all samples were diluted by a factor of two.