Method for producing derivative of organic substance and method for analyzing sample containing organic substance

A method for analyzing a sample containing an organic substance, comprising:

• (1) mixing a sample containing an organic substance containing one or more groups selected from the group consisting of sulfanyl, selanyl and sulfino, and an olefin compound containing an ethylene structure having at least two electron-withdrawing groups except halogen atoms under an acidic condition to form a treated sample containing a derivative of the organic substance;
• and
• (2) analyzing the derivative of the organic substance in the treated sample,
• wherein the olefin compound is N-ethylmaleimide or a compound represented by formula (I):
• wherein
• EWG1 and EWG2 each independently represent —C(═O)—OR1, —S(═O)2—R2, —P(═O)(—OR3)2, cyano, a halogen atom-substituted alkyl, carboxy, nitro, —S(═O)—R4, —C(═O)—R5 or —C(═O)—NR6R7, and
• EWG1 and EWG2 optionally form a ring together with the carbon atom to which EWG1 and EWG2 are bonded,
• wherein
• R1, R2, R3 and R4 each independently represent a monovalent hydrocarbon group or a monovalent heterocyclic group and optionally each have a substituent, and
• R5, R6 and R7 each independently represent a hydrogen atom, a monovalent hydrocarbon group or a monovalent heterocyclic group and optionally each have a substituent.