Pre-dry the glass fiber micro-filters in the drying cabinet at 105 °C for about 2 hours.After cooling down of the filters in the desiccator, determine the mass of a filter m E. Place the weighed filter in the Büchner funnel. Measure 100 ml of a homogeneous (press) water sample using a graduated cylinder V ml. The Büchner funnel with the filter is placed on a suction bottle and the press water sample is filtered by means of a vacuum. Then, remove the filter and dry it in the drying cabinet at 105 °C until constant mass (according to 2.1.7).After cooling down in the desiccator, determine the mass of the filter by means of an analytical balance m A.