Analysis of amino acids in biological fluids by pentafluorobenzyl chloroformate derivatization and detection by electron capture negative ionization mass spectrometry.

Pentafluorobenzyl chloroformate (PFBCF) has been utilized as a derivatization reagent for amino acids (AAs) in biological fluids with susequent detection by electron capture negative ionization mass spectrometry (ECNI/MS). AAs were derivatized in one step in aqueous solution, plasma, and whole blood at room temperature. To demonstrate quantitative analysis, phenylalanine concentrations were determined in human plasma. AAs were derivatized in one step using PFBCF and a mixture of water, ethanol, and pyridine/dimethylaminopyridine. The N-pentafluorobenzyloxycarbonyl amino acid ethyl esters (f phi-AA-OEt) exhibited good GC properties and the ECNI mass spectra are dominated by the [M-181]- ion. The f phi-AA-OEt derivatives can be easily detected at the femtomole level by selected ion monitoring. Phenethyl alcohol was also derivatized, using anhydrous conditions, and the resulting PFB carbonate's ECNI mass spectrum was dominated by the [M-181]- ion. The ECNI molar response of the PFB carbonate derivative is two times that of the corresponding pentafluorobenzoate.