Influence of filtration, preservation and storing on the analysis of low molecular weight organic acids in natural waters

The suitability of three filter materials (polycarbonate, cellulose acetate and glass fibre) for trace organic acids analysis (acetic, butyric, B-hydr oxy-butyric, formic, lactic, maleic, methyl-succinic, malonic, oxalic, succ inic and valeric) was tested by determining leached components and sorption /desorption properties. Analysis of the organic acids was made with capilla ry zone electrophoresis (CZE). Polycarbonate membranes were easily cleaned by leaching with Milli-Q water and showed limited adsorption of the acids. Cellulose acetate filters requi red a more elaborate washing before use and had a higher retention capacity . Glassfibre filters are not recommended due to severe contamination of org anic compounds and release of colloids. Preservation of natural water samples (eutrophic, dystrophic) by addition o f chloroform, sterile filtration and freezing (-20 degrees C) were quantita tively evaluated, after spiking with the organic acids (500 mu g/1 each) an d storing for 11 weeks. Freezing was the only treatment where the added acids were quantitatively r ecovered after 4 weeks. Sterile filtration in combination with storing of t he samples in the dark at 4 degrees C can be suitable for short time preser vation (less than 30 days). However, these conditions resulted in a high va riation of recovered amounts among the replicates. Storing of untreated sam ples at room temperature or in a refrigerator, as well as addition of chlor oform should be avoided. (C) 1999 Elsevier Science Ltd. All rights reserved .