NOTE: GAC = granular activated carbon; MW = molecular weight.
a Molecular weight calculated for the propylated derivative, obtained from i-butane chemical ionization mass spectrum.
b Chemical name in parentheses indicates the parent compound.
c A compound was considered positively identified if the spectra for the compound agreed with reference spectra from the National Biological Survey and EPA-National Institutes of Health libraries or if both its retention time and spectra agreed with those of a standard, reference compound.
d Brominated compounds only found in chlorinated GAC effluent.
e N—not identified.
SOURCE: Reprinted, with permission, from Ding et al., 1996. © 1996 by Springer-Verlag, New York.
for in vitro and in vivo toxicity testing of reclaimed water. Substantial advances in these techniques can be attributed to improvements in three areas:
Although the quality of the reagents and instrumentation for carrying out these tasks has improved in recent years, the basic approaches have not changed. Rather, the techniques have been better integrated, making the distinctions among them less critical. The most advanced chemical characterization methods involve an extensive combination of concentration, isolation, and analytical steps.
Techniques for concentrating nonvolatile organics include low-temperature evaporation, membrane processes (reverse osmosis and nanofiltration), and adsorption/desorption using macroreticular resins as the adsorbent followed by elution by a solvent or by changing the pH. Liquid or gas chromatography is often used to further isolate analytes, followed by mass spectrometry for identification of specific compounds.
Techniques for concentrating chemical contaminants by removing water from the sample pose a notable challenge—that of achieving the required concentration without the concentrated compounds interacting and creating a solution or solid substantially different from the starting