Reagent contact time determination

Whether the Mattole River sample of Kennedy et al. Q2) contained a significant amount of Alb cannot be determined from the data they presented. Colloidal particulates that perhaps contained Ale were probably present in material passing through the 0.45 pm filter. The extraction procedure used in their experiments involved a 15 minute contact time of the 8 quinolinol reagent with the sample making it likely that some, at least, of the Alb fraction would be extracted. The method of Barnes (28) uses the same extractant but only a 10 sec. contact time, in order to minimize extraction of polymeric Al species. 

Both the gel and toluene soluble fi actions are reserved for determination of unsaturation by the iodine monochloride method. To determine unsaturation in styrene-butadiene rubbers with good accuracy using the iodine monochloride procedure it was found necessary to contact the sample with chloroform for 15 hours before reaction with iodine monochloride. Even with a 30 hour reaction period, a constant iodine value (ca. 20) is obtained only when the sample size is O.OSg or less, ie. a five-fold excess of iodine monochloride reagent. The solid gel, separated from a high impact polystyrene by the solvent extraction procedure, is completely insoluble in chloroform and in the iodine monochloride reagent solution. A contact time with chloroform of 90 hours with a 75 hour reaction period with reagent is required. 

Basically the experimental parameters affecting the sorption behavior in simple systems (concentration of the adsorbate, solid to liquid ratio, equilibration time, temperature, pH, and ionic strength) are also important in sorption competition. Thus, Table 4.7 has the same columns as Tables 4.1 and 4.2 (specific adsorption in absence of competitors). In simple systems little attention is usually paid to the sequence of addition of reagents, but in studies of sorption competition this factor must not be neglected. The fact that some adsorbate is added (brought in contact with the adsorbent) first makes it a more successful competitor. Let us consider the following experiment. The adsorbent is equilibrated with solution of adsorbate I (adsorbate of interest), then the adsorbent is separated from the solution and contacted with solution of adsorbate 2 (competitor), and then the concentration of adsorbate 1 in solution is determined after certain equilibration time. Only a fraction of adsorbate 1 is released even if adsorbate 2 is a very strong competitor. However, adsorbate 2 added first or simultaneously with adsorbate I would completely prevent sorption of adsorbate 1 at otherwise identical experimental conditions. 

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