The invention relates to a filtering method for isolating and/or quantifying, from a sample, at least one substance to be investigated, comprising: - introducing, via a sample inlet (3a), a first quantity of the sample into a filter module (2) which has a housing (3) with a first opening forming the sample inlet (3a) and a second opening which is covered by a filter (4) and forms a sample outlet (3b), wherein the filter (4) is designed to hold back a first portion of the sample and to allow a second portion of the sample to pass through; - conducting the sample from the sample inlet (3a) through the filter (4) and the sample outlet (3b) by applying a pressure difference between a side of the filter (4) facing the sample inlet (3a) and a side of the filter (4) facing away from the sample inlet (3a), wherein the second portion of the sample leaves the filter module (2) through the sample outlet (3b) as a filtrate; - while the sample is being conducted from the sample inlet (3A) through the filter (4) to the sample outlet (3b), detecting a series of temporally sequentially recorded measurement values of a measurement variable which represents the pressure difference and/or a volumetric flow through the filter (4); - comparing the measurement values to a predefined reference value of the measurement variable; and - ending the filtering method if successively detected measurement values of the measurement variable, over a predefined timespan, are equal to the reference value and/or lie within a predefined range of values around the reference value. The invention also relates to a device with which the method can be carried out.
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