Cayman's AMP+ MaxSpec? Kit contains a positively charged reagent (AMP+) that can be coupled quantitatively to free carboxylic acids through an amide bond linkage. The resulting derivatized product thus contains a positively charged group that shows improved electrospray ionization and consequently improved MS sensitivity. The derivatization reagent is stable to MS/MS fragmentation and thus isobaric derivatives undergo compound-specific fragmentation to give unique fragment ions.