Anion-exchange retention process

FIGURE 1.3 Enantiomer separation of the chiral acid iV-acetyl-a-allyl-glycine on CHIR-ALPAK QN-AX (a) and CHIRALPAK QD-AX (b) by an enantioselective anion-exchange retention process. Chromatographic conditions Column dimension, 150 x 4 mm ID eluent, 1 % (v/v) glacial acetic acid in methanol flow rate, 1 mLmin temperature, 25°C detection, UV 230 nm. (Reproduced from M. Lammerhofer, et ah, Nachrichten aus der Chemie, 50 1037 (2002). With permission.)... 

Even in this case, the use of a hybrid process combining NF, IE, and ED appears to improve the economics and performance of the tartaric stabilization of wines. For instance, Ferrarini (2001) proposed to split raw wine into a retentate and permeate by NF. The permeate, being richer in minerals, was processed by using in sequence cationic and anionic exchange resins and ED to reduce its potassium, calcium, and tartrate ion contents. By recombining the de-ashed permeate with the NF retentate, Ferrarini (2001) asserted to obtain a stabilized wine retaining almost all the flavor and aroma compounds originally present in raw wine. 

Analysis of Nontarget Compounds. "Complete Unknowns. This is a somewhat similar process in that the retention time and the type of LC column giving the best results also yields dues as to chemical classification, e.g., good retention and separation upon an anion exchange column suggests that the analytes are anionic. Confirmation information required for unknown identification is also obtained from other instrumentation induding UV spectrophotometry. 

Fig. 3-13 shows the influence of the above-mentioned parameters on the separation of simple inorganic anions. It is evident from looking at Fig. 3-13 that the elution order of anions, which are separated exclusively via anion exchange processes, cannot be altered. An exception are polyvalent ions, because their valency and thus their retention are a function of the pH value. 

To understand better the sorption process of dyes of various types of anion exchange resins, it is essential to determine the course of this process in time and the effect of different factors affecting their retention. The rate at which the dissolved dye is removed horn the aqueous solution by solid sorbents is a significant factor for application in wastewater quality control, too. It is essential to evaluate the adsorption kinetics using theoretical models in order to design and control the sorption process units. Two common kinetic models, namely, the Lagergren pseudo first-order model (Equation 4) and the Ho and McKay pseudo second-order model (Equation 5) were fitted to the experimental data of dyes sorption on the anion exchangers ... 

Even more advantageous is the fact that with the concentration of the feed mixture increasing, the distance between the fronts of the two components under separation noticeably increases. This corresponds to an increase in the separation selectivity, which further enhances the productivity of the process. An analogous phenomenon was first observed by Nelson and Kraus [116] in 1958 in the separation of concentrated solutions of LiCl from HCl on the anion-exchange resin Dowex-lxlO. The prolonged retention of HCl at increasing LiCl concentration was explained at that time by the authors as due to a drop of the activity coefficient of HCl in the resin phase (which, obviously, was not a correct explanation). 

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