Patent ID: 8278117

Claim:
A method of mass spectrometry comprising a step of dispersing CuO secondary particles each comprising an aggregate of CuO primary particles with an average particle diameter of 100 nm or smaller and having an uneven surface arising from the shape formed by the primary articles constituting the outermost surface of the secondary particle wherein the CuO secondary particle is derived from a CuO powder produced by baking basic copper carbonate in air at 200 to 300° C. and wherein the basic copper carbonate is produced in a process of mixing an aqueous ammonium hydrogen carbonate solution and an aqueous copper nitrate solution by a neutralizing operation wherein the aqueous ammonium hydrogen carbonate solution is stirred, and the aqueous copper nitrate solution is continuously added thereto, in a liquid medium; a step of applying the dispersion onto a sample substrate for MALDI mass spectrometry followed by drying it thereon to give a sample holder carrying the CuO secondary particles therein; a step of applying a sample solution of an organic compound (sample substance) to be analyzed, as dissolved therein, onto the CuO secondary particles-carrying sites of the sample holder followed by drying it thereon to make the sample substance adhere to CuO; and a step of setting the sample holder in a MALDI mass spectrometer followed by irradiating it with pulse laser so as to make the CuO secondary particles function as a laser-beam-absorbing matrix to ionize the sample substance.