Identification of Bromohydrins in Ozonated Waters

Abstract

Because ozonation is becoming a popular alternative to chlorination for disinfection of drinking water and little is known about the potential adverse health effects of ozonation disinfection by-products (DBPs), we have sought to identify ozone DBPs, particularly brominated organics, which are of principal concern due to their anticipated toxicity. Using gas chromatography coupled (independently) to low-resolution electron-impact mass spectrometry (LR-EI-MS), high-resolution EI-MS, chemical ionization MS (with 2% ammonia in methane), and Fourier transform infrared spectrometry, we have identified a series of bromohydrins and related compounds detected in extracts of an ozonated natural water sample that was artificially enhanced with bromide. The bromohydrins, which constituted the majority of by-products in the samples we studied, were detected but could not be identified by GC/LR-EI-MS, the technique used almost exclusively for environmental monitoring. A key to identifying the bromohydrins was the manifestation of intramolecular hydrogen bonding in the gas-phase IR spectra. Many of the by-products had two chiral centers, and both diastereomers were present and were separated by GC. In most cases, the IR spectra also permitted us to distinguish between diastereomers. We interpreted the IR and EI-MS spectra of several representative compounds in detail, and gave peak assignments for all that were identified. Molecular mechanics calculations and an experimental determination of the enthalpy change for conversion of free and hydrogen-bound conformers for a representative bromohydrin were used to verify the IR interpretations.