Selecting filter membranes for measuring DOC and UV254

Seventeen filter membranes produced from eight membrane materials by four major manufacturers were evaluated for dissolved organic carbon (DOC) and ultraviolet (UV254) absorbance measurements and thus for specific UV absorbance determinations. Hydrophilic polyethersulfone filters from two manufacturers and a hydrophilic polypropylene filter were the best options among the filters tested for complying with the US Environmental Protection Agency's Disinfectants/Disinfection By-products Rule. These filters should be rinsed with a minimum of 30 mL distilled and deionized water/cm(2) filter surface area (e.g., 500 mL on a 47-mm disc filter) prior to use. During sample filtration, an initial 25 mL of the filtrate on a 47-mm filter must be wasted before samples for DOC and UV254 measurements are collected to minimize the impact of dissolved organic matter (DOM) losses to filter membranes. Other filters were not recommended because of one or a combination of the following factors: (1) they did not have an absolute pore size of 0.45-mum, (2) they exhibited higher degrees of organic carbon leaching and were more difficult to render clean, and/or (3) they showed significant DOM uptake. Before a filter for DOC and UV254 measurements is selected, it is essential to conduct filtered blank experiments and to demonstrate that there is no gain or loss of DOC and UV254 during filtration. It is also important to recognize that there may be significant lot-to-lot variations in the levels of contamination on filters.