USE OF MEMBRANE FILTERS IN GRAVIMETRIC ANALYSES OF PARTICULATE MATTER IN NATURAL WATERS

The weights of membrane filters used in gravimetric analysis of water were significantly changed by electrostatic charge, leachable material within the filters, and absorption of atmospheric moisture. Millipore type HA filters lost an average of 0.31 ± 0.07 mg or 0.32% of their dry weight as leachable material when 6 liters of distilled water were filtered. About 165 ml were required to remove 50% of the total leachable material removed by 1000 ml. These filters absorbed moisture from the atmosphere very rapidly during the first minute of exposure and at a much slower rate thereafter. The leachable material contributed to moisture absorption. Desirable drying temperature and time for Millipore type HA filters was determined. Other filters were compared; recommendations for the use of these filters are given. Copyright 1969 by the American Geophysical Union.