Methods, mixtures, kits and compositions pertaining to analyte determination

The present invention is the mass spectrometry using the set consisting of a peculiar sign-ized reagent or a peculiar sign-ized reagent, and relates to the method for measuring an analysis thing, a mixture, a kit, and/or a composite. A sign-ized reagent is isomer isobar-like and can be used for generation of a mixture suitable for multiplexing analysis of a sign analysis thing. The sign of an analysis thing can make this analysis thing able to react to the sign-ized reagent which is a compound of formula RP*X*LK*Y*RG, or its salt, and can be performed. Two or more sets can carry out [isomer] the sign of the analysis thing which consists of two or more kinds of different samples using an isobar sign-ized reagent.