Pentafluorobenzyl chloroformate (PFB-chloroformate) has been utilized as a derivatization reagent to impart electron affinity and provide structurally relevant fragmentation in electron capture negative ion chemical ionization mass spectrometry (ECNICI-MS). Phenylalanine (Phe) and decanol were used as model analytes. The conditions used for their derivatization and the chromatographic and mass spectrometric properties of the derivatives are reported. Phenylalanine in aqueous solution was derivatized in one step by using PFB-chloroformate and a mixture of water, ethanol, and pyridine. The phenylalanine N-pentafluorobenzyl-oxycarbonyl ethyl ester (N-PFBC-Phe-OEt) exhibited good gas chromatographic properties and in ECNICI-MS, a dominant M - 181 fragment carries most of the ion current. Selected ion monitoring experiments on N-PFBC-Phe-OEt resulted in the facile detection of 400 fmol of material. Decanol was derivatized by using anhydrous conditions, and the resultant pentafluorobenzyl carbonate also exhibited a predominant M - 181 ion in ECNICI-MS. Initial results indicate that the ECNICI-MS molar response of the decyl pentafluorobenzyl carbonate derivative is six-fold that of the decyl pentafluorobenzoate.