Because the rate of naphthenic acid corrosion does not correlate with the concentration of acids, it has been proposed that a subset of naphthenic acids in petroleum fractions may be more corrosive than others. The primary corrosion products (iron naphthenates) decompose to form ketones at corrosion temperatures (250-400 degrees C), so characterization of ketones in corrosion fluids could potentially be used to identify the reactive acids that generated the iron naphthenate. Previous work with model acids has reported the development of a method to characterize such ketones by isolation with strong anion exchange separation and detection, with the assistance of ketone targeting derivatization reagent, by Fourier transform ion cyclotron resonance mass spectrometry. Here, we extend that method to characterize the ketones formed in a corrosion test by use of commercially available naphthenic acids (NAP) in a flow-through reactor. The NAP corrosion test yields a single 01 ketones/aldehydes distribution close to that predicted from the O-2 acids distribution before corrosion, with no bias in the carbon number and a slight bias toward lower double bond equivalents in the reactive acids detected. Ketone distributions did not appear to change over the 24 h test. With a fluid residence time of only similar to 30 min at reactor temperature, the results suggest that the ketones were formed rapidly beneath an FeS scale.