Anion typical separations

The Na is 555 pm from the nearest N and 516 pm from the nearest O, indicating that it is a separate entity in the structure. Potas-sides, rubidides and caesides have similarly been prepared. The same technique has been used to prepare solutions and even crystals of electrides, in which trapped electrons can play the role of anion. Typical examples are [K(cryptand)]+e and [Cs(18-crown-... 

The cyclic group 14 polyanions are usually found in ternary materials that contain two types of cations which, in addition to providing charge balance, perform different roles. The structures typically consist of cyclic polyanions that are stacked in an eclipsed fashion to form columns. One type of cation coordinates to the anions and separates them within the column, whereas the second type segregates the columns. These ternary materials are typically prepared by heating stoichiometric amounts of the three elements in an unreactive metal tube, e.g. niobium, at very high temperatures (>800°C) followed by slow annealing at lower temperatures. 

Some typical separations of these anions achieved are shown in Fig. 2.18. Fig. 2.18(a),(b) illustrates ion chromatographic separations of mono and diprotic organic acids by ion exchange using anodic AMMS and CMMS micromembrane suppressors. 

Ion-exchange (or ion) chromatography uses vertical columns loaded with ionic resins with either mobile anions or mobile cations (typically acidic cations and aminium anions) to separate ionic salts dissolved in water. These resins can separate even rare earth salts from each other and would have been a godsend to Marie Curie The charge, polarizability, and size of the solvated ion and the properties of the anionic or cationic resins are factors that influence the separability. 

Figure 33-10 illustrates the un.surpassed quickness and resolution of electrophoretic separations of small anions. Here, 30 anions were separated cleanly in just over 3 minutes. Typically, an ion-exchange separation of only three or four anions could be accomplished in this brief time period. Figure 33-11 further illustrates the speed at which separations can be carried out. Here, 19 cations were separated in less than 2 minutes. 

In the experimental system, the capillary is filled with electrolyte with each end open to a separate reservoir of electrolyte. When a voltage is applied, an electric current is established in which electrolyte anions migrate toward the positive electrode (anode) and electrolyte cations move in the opposite direction. After sample injection, sample anions are separated by differences in their electrophoretic migration rates to the detector at the anodic end of the capillary. Although the sample anions migrate against a counter flow of electrolyte cations, interaction between the cations and anions is minimal in conventional CE where the background electrolyte typically contains a fairly low concentration of sodium or ammonium cations. 

As a typical example for an anion-exchange separation of an organic acid under isocratic conditions. Figure 10.290 shows the analysis of propanephosphonic acid... 

In the past, the most common method for analysis of small anions has been ion chromatography. For cations, the preferred techniques have been atomic absorption spectroscopy and ICPMS. Figure 30-1(1 illustrates the speed and resolution of electrophoretic separations of small anions. Here, thirty anions were separated cleanly in just more than 3 minutes. Typically, an ion-exchange separation of only three or four anions can be accomplished in this brief period. Figure 30-11 further illustrates the speed at which separations can be carried out. In this example, nineteen cations were separated in less than 2 minutes. CE methods were once predicted to replace the more established methods because of lowerequipment costs, smaller-sample-size requirements, and shorter analysis times. However, because variations in electroosmotic flow rates make reproducing CE separations difficult, LC methods and... 

The majority of HPLC applications in the determination of anionic surfactants are only concerned with the analysis of LAS, which are the surfactants in the largest quantities in present detergent formulations. Individual homologs of LAS are typically separated on... 

Flotation reagents are used in the froth flotation process to (/) enhance hydrophobicity, (2) control selectivity, (J) enhance recovery and grade, and (4) affect the velocity (kinetics) of the separation process. These chemicals are classified based on utili2ation collector, frother, auxiUary reagent, or based on reagent chemistry polar, nonpolar, and anionic, cationic, nonionic, and amphoteric. The active groups of the reagent molecules are typically carboxylates, xanthates, sulfates or sulfonates, and ammonium salts. 

Hplc techniques are used to routinely separate and quantify less volatile compounds. The hplc columns used to affect this separation are selected based on the constituents of interest. They are typically reverse phase or anion exchange in nature. The constituents routinely assayed in this type of analysis are those high in molecular weight or low in volatility. Specific compounds of interest include wood sugars, vanillin, and tannin complexes. The most common types of hplc detectors employed in the analysis of distilled spirits are the refractive index detector and the ultraviolet detector. Additionally, the recent introduction of the photodiode array detector is making a significant impact in the analysis of distilled spirits. 

A typical application of ion chromatography for the separation and determination of simple anions is illustrated by the experiment described in Section 7.15. 

It is apparent that, as in chemical systems, the magnitude of these effects will become useful and interesting from a practical viewpoint only when the pressure is increased above one kilobar. Thus for a typical electron transfer reaction with JF"=—20 cm mole , AE will be 211 mV when the pressme is ten kilobars. This shift could be important in the not uncommon situation where, at atmospheric pressure, the oxidation of a neutral substrate occurs at around the same potential as the anion of the base electrolyte. An increase in the pressure to ten kilobars will result in a separation of the processes... 

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