Evaluation of Fluorinated Indole Derivatives for Electron‐capture Negative Ionization Mass Spectrometry: Application to the Measurement of Endogenous 5‐Methoxyindole‐3‐Acetic Acid in Rat

A series of N-trifluoroacetyl/pentafluoropropionyl-O-trifluoroethyl/ pentafluoropropyl/heptafluorobutyl ester derivatives of 5-methoxyindole-3-acetic acid (5MIAA) were synthesized. Under electron-capture negative ionization conditions, the N-trifluoroacetyl derivatives were found to yield relatively abundant, analyte-specific M-. molecular ions and [M-HF]-., [M-HF-CF2CO]-. and [M-CF3CO]- fragment ions, while the N-pentafluoropropionyl …