Method for preparing peptide fragments, kit for preparing peptide fragments to be used therein, and analysis method

An analytical method, comprising:

• proteolyzing a protein in a sample such that a peptide fragment is produced;
• and
• identifying or quantifying the peptide fragment in the sample by mass spectrometry,
• wherein the proteolyzing includes immobilizing the protein in at least one pore of a porous body, and contacting the protein immobilized in the pore and a protease immobilized on a solid surface such that the protease selectively accesses a site of the protein and proteolyzes the protein at the site.