Heterogeneous nitration rates of the aromatic organic compound 1, 3-bis(trifluoromethyl)benzene in a well-agitated batch system have been measured in an extensive range of very concentrated mixed acids (aqueous HN0 3 and H 2 SO 4), with each run at essentially constant acid composition. The observed conversions correlated well with a firstorder dependence on the fraction of aromatic unconverted. Solubilities of the aromatic compound have been measured over the range of acid compositions.
Several potential sources of variation in steric exclusion chromatography (SEC) are discussed: flow rate stability of the pump, column temperature, data processing, and the chromatography itself. Many of these variation sources may be minimized by careful attention to analytical techniques. Flow-rate stability, however, is a function of the chromatographic hardware used and is not as readily subject to control. Experimental techniques are described whereby relative standard deviations below 0.3% in the routine determinations of molecular-weight averages may be achieved on an optimized chromatographic system.
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