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COMPARISON OF PERFLUORINATED CHLOROFORMATES AS DIRECT AQUEOUS SAMPLE DERIVATIZING AGENTS FOR HIGHLY HYDROPHILIC ANALYTES
Citation:
Vincenti, M., P. Davit, AND S D. Richardson. COMPARISON OF PERFLUORINATED CHLOROFORMATES AS DIRECT AQUEOUS SAMPLE DERIVATIZING AGENTS FOR HIGHLY HYDROPHILIC ANALYTES. Presented at 50th American Society for Mass Spectrometry Conference, Orlando, FL, June 2-6, 2002.
Impact/Purpose:
Determine the actual concentrations of suspected health-impacting DBPs produced using non-chlorine disinfectants, how often they occur, under what conditions they are formed, and their fate and transport in the distribution system.
Description:
Strong oxidants are supposed to produce quite extensive cleavage of the hydrocarbon backbone of natural organic matter, resulting in the release of partly oxidized organic molecules. The identification and detection of these small and highly polar compounds represents a challenging task, since they cannot be extracted from the aqueous matrix or concentrated. Moreover, their direct instrumental detection in the original matrix is difficult due to inadequate sensitivity, lack of chromophores for spectroscopic detection, and low and noisy molecular ion signal for mass spectrometric detection. Typical analytes of this kind are polycarboxylic acids, hydroxyacids, ketoacids, glyoxals, hydroxylamines, aminoacids, aminoalcohols, and glycols. Direct aqueous sample derivatization is a promising approach to convert the analyte polar functional groups into more hydrophobic ones, allowing their extraction. However, most derivatizing agents are instantly hydrolyzed as they interact with water-containing solvents. We have developed a series of derivatization procedures based on hydrophobic chloroformates, which operate preferentially in purely aqueous solutions, while the addition of any organic solvent disfavors, instead of favoring, the derivatization yields. The commercially available prototype of these hydrophobic reagents is n-hexyl chloroformate. We have recently synthesized a series of perfluoroalkyl and perfluoroaryl chloroformates, in order to produce more volatile derivatives and to achieve high sensitivity and selectivity by electron capture negative ionization MS detection. The series of perfluorinated chloroformates that we have synthesized includes 2,2,3,3,4,4,5,5-octafluoropentyl, 2-chloro-2,2,3,3,4,4,5,5-octafluoropentyl, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl, pentafluorobenzyl, and 2-(pentafluorophenoxy)ethyl chloroformates. Upon derivatization, carboxylic acids, alcohols, and amines are converted into esters, carbonates, and carbamates, respectively, which have no more hydrophilic character. When multiple functional groups are present in a single analyte structure, each one undergoes derivatizatization. The applicability and analytical performance of these five chloroformates for the derivatization of polar analytes in the aqueous-phase was compared, revealing interesting differences and preferences. The large number of fluorine atoms in the derivative structures confers high electron affinity to them, allowing extremely sensitive detection by ECNI-MS. Unfortunately, the ECNI mass spectra of the derivatives exhibit extensive fragmentation, which often prevents the detection of the molecular ion. On the other hand, positive ion CI spectra are more likely to provide the molecular ion information, but the detection limits in the positive ion mode is 3 orders-of-magnitude higher than in the negative ion mode. In the negative ion mode, the detection limits for most standard analytes are located in the low ppt range, as referred to the original concntration in water. Calibration curves are linear in a two orders-of-magnitude range.