Phosphonium compound, reagent kit for derivatization, mass spectrometric method, and method for producing phosphonium compound

A phosphonium compound represented by Formula (I):

• wherein in Formula (I),
• R1 is an alkyl group, the alkyl group being a substituted or unsubstituted, linear or branched alkyl group having 1 to 20 carbon atoms or a substituted or unsubstituted cyclic alkyl group having 5 to 20 carbon atoms;
• and
• R2 and R3 are independently from each other, an alkyl group or an aryl group,
• the alkyl group is a substituted or unsubstituted, linear or branched alkyl group having 1 to 20 carbon atoms or a substituted or unsubstituted cyclic alkyl group having 5 to 20 carbon atoms, and
• the aryl group is a substituted or unsubstituted aryl group having 6 to 20 carbon atoms;
• wherein X is a group having a hydrazide group, a halide group, a pseudohalide group, or a thioester group, and
• when X is the group having the hydrazide group, the group is
• wherein o is any integer of 0 to 6;
• when X is the group having the halide group or the pseudohalide group, the group is
• wherein W is a halogen or a pseudohalogen, and p is any integer of 0 to 6;
• or
• when X is the group having the thioester group, the group is
• wherein V is H, NH2, a sulfonate ion group SO3−, SO3M, COO−, or COOM, and M is a hydrogen atom, a lithium atom, a sodium atom, or a potassium atom;
• and
• Y− is an anion having a total charge of −1, or Y− is absence.