Characterization of natural organic matter using high performance size exclusion chromatography

High performance size exclusion chromatography (HPSEC) was used to obtain t he molecular weight distributions of natural organic matter (NOM) from two South Australian drinking water sources. The NOM was separated into five no minal molecular weight fractions (<500, 500-3K, 3K-10K, 10K-30K, and >30K) using ultrafiltration membranes prior to HPSEC analysis. The use of HPSEC a s a tool for NOM characterization was compared with an independent method, flow field-flow fractionation (FIFFF), which separates molecules via a diff erent mechanism. Unlike HPSEC, which uses a porous gel with a controlled po re size distribution to separate molecules, FIFFF uses hydrodynamic and mol ecular diffusion principles to separate molecules on the basis of molecular size, in the absence of a porous gel. The comparison was made using the fo llowing parameters: weight-average molecular weight (M-w), number-average m olecular weight (M-n), peak molecular weight (M-p), polydispersivity (M-w/M -n), and molecular weight range (80% confidence limits). Within the technic al limitations of each method, good agreement was obtained between HPSEC an d FIFFF for the different fractions. Although solute-gel interactions were identified with the HPSEC system, the validation of the technique with FIFF F indicates that HPSEC can provide useful and reliable molecular weight dis tributions of NOM in drinking water supplies.