Hollow fiber cartridges for removal of particulate matter from natural waters prior to matrix isolation and trace metal enrichment using an 8-quinolinol chelating ion exchanger in a flow system

Natural water samples are normally filtered through a 0.45 μm membrane filter before analysis. Such filters clog rapidly, however, when the content of humic acids is high. An alternative approach for natural water filtration is reported in this paper. Sample solutions are pumped into tubing containing a coaxial hollow fiber and a needle valve restrictor at the outlet. One end of the hollow fiber is plugged and the other is connected to a chelating ion exchange column for uptake of trace metal ions. The differential pressure between the inside and the outside of the fiber forces a filtered liquid through the fiber and into the ion exchanger. It was found that flow rates of about 2.0 ml min−1 could be obtained with a pressure difference of around 1 bar. The concentrations of copper, cadmium and cobalt ions were the same in the filtrate as in the inlet solution, indicating that the membrane is uncharged. In one configuration more than 4 I of a sample containing 20 μg ml−1 humic acids could be passed through the fiber before clogging caused unacceptable reduction of the flow rate. A hollow fiber cartridge, therefore, seems to be very useful for enrichment of ions from samples with a high solids content. The trace metals were enriched about 15 times using the described procedure.