Determination of copper speciation in freshwater samples through SPE-spectrophotometry

The Cu(I)-bathocuproine complex was separated by solid phase extraction (SPE) on octadecyl (C18) bonded silica cartridges or disks followed by elution and spectrophotometric detection (SPE-spectrophotometry) and applied as a detection and speciation method for Cu in water samples. For a PTFE-supported C18 disk, the bathocuproine-available copper detection limit of 0.4 μg l−1 for ultrapure water (500 ml sample) was raised to 3.8 μg l−1 in polluted water due to filter blockage by colloids. UV irradiation gave total copper analysis, no filter blockage and a lower detection limit. Repeated analysis of drinking water gave a standard deviation of ±1%, correct concentration was determined in certified riverine water and a satisfactory result was obtained in an interlaboratory calibration for Cu in freshwater. A comparison of C18 cartridges and disks for direct analysis of water samples showed long filtration times for a C18 cartridge and high blanks for a glass fibre-supported C18 disk; PTFE-supported C18 disks gave rapid filtration and low blanks in both filtered and unfiltered water samples. A significant difference was noted for Cu determination in the presence of NTA (nitrilotriacetic acid) when bathocuproine was immobilised on the disk rather than pre-equilibrated with Cu, and interpreted in terms of lability of the Cu NTA complex and short contact time with bathocuproine on the disk. In speciation analysis, SPE-spectrophotometry is sensitive, precise and convenient for freshwater samples and has the advantage over electrochemical analysis at a Hg electrode of being a Hg-free method.