To provide a method for acquiring a solution from which a material interfering with detection of a trace component when performing clinical proteome analysis is removed.

Undiluted solution is not excessively concentrated or diluted in a fractionation solution circulation circuit, and concentration polarization is kept in a proper range, to thereby remove efficiently an interfering material having a high molecular weight. The solution acquired by a separation film is used for protein analysis such as mass spectrometry, electrophoresis or liquid chromatography, and high-sensitivity analysis becomes possible.