THE EFFECT OF USING DIFFERENT 0.45-MU-M FILTER MEMBRANES ON DISSOLVEDELEMENT CONCENTRATIONS IN NATURAL-WATERS

The effect of 4 different 0.45 mu m pore size filter membrane systems on the 'dissolved' concentration of 28 elements in 5 natural water sam ples of varying matrix is reported. In 3 of the 5 waters, consistently higher concentrations of most elements (minor and trace) are obtained using Nucleopore 47 mm filter and the cellulose acetate/nitrate 47 mm filter than those measured using the 142 mm cellulose nitrate MFS fil ter or the Gelman capsule 47 mm filter. These distinct and coherent pa tterns in elemental behaviour disappear for the other 2 samples, an or ganic-rich peat water of high suspended load and a mineralised sample high in Si and Ca. Thus the nature and degree of filtration artifacts is matrix-dependent. These trends are evident in both data sets produc ed by 2 independent laboratories using different instrumentation, tech niques and calibrating procedures. The average relative standard devia tion in elemental concentration across the 4 filter types is in the ra nge 9-21 %. The presence of such filtration artifacts must be consider ed in projects where, for example, seasonal variability of water compo sition is under examination, data from various sources are being merge d or hydrogeochemical surveys are being conducted. Copyright (C) 1996 Elsevier Science Ltd