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Organic contaminants at concentrations of parts per billion or less may modify water quality significantly. However, even the most sensitive of the available analytical procedures are not capable of quantitative identification at these trace levels. Thus, the organics must be concentrated prior to analyses. Freezing was evaluated as a concentration technique. As solute-containing aqueous solutions are frozen, the ice which crystallizes initially is very pure. The solutes are rejected into the unfrozen liquid. If the process is interrupted prior to complete solidification, the residual liquid will be considerably enriched.
Recovery of micrograms per liter and milligrams per liter concentrations of various organics from aqueous solutions was studied. In the absence of dissolved inorganic salts mixing rate is not a factor. Organic dissociation potential; molecular size and weight; and nature, location, and number of substituent groups have no effect. However, dissolved salts impair organic solute rejection and in this case higher mixing rates promote recovery. An interrelationship between total dissolved salt content, mixing rate, and efficiency of organic solute recovery was demonstrated. Most important, for the systems studied, it was shown that although complete organic recovery was not achieved, all components of complex mixtures were recovered with equal efficiency. Thus, an analytical procedure making use of additions of known organic materials to serve as internal standards is suggested.
concentrating, organic compounds, water, organic analyses, freezing, evaluation, tests
Senior fellow, Mellon Institute, Carnegie-Mellon University, Pittsburgh, Pa.