Mixtures of anions and cations

Ion chromatography is not restricted to the separate analysis of only anions or cations. With the proper selection of eluant and separation columns, the technique can be used for the simultaneous analysis of both anions and cations. 

Instruments Electrochemical applied Dionex model 201 Oi ion chromatograph Dionex electrochemical detector Houston Instrument Omniscribe chart recorder 

Suppressor column Dionex AMS, preproduction protot/pe. Membrane suppressor 

Eluant 0.00l6mol L, LijCOj + 0.0024mol L- LiCOOH.HjO pH = 10.4 Monovalent cations and anions 

Cation separator Eluant Separator columns 200 X 4mm id Dionex HPIC-CS1 cation 0.0033mol L Cu phthalate divalent cations and anions 

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In the case of ions, the repulsive interaction can be altered to an attractive interaction if an ion of opposite charge is simultaneously adsorbed. In a solution containing inhibitive anions and cations the adsorption of both ions may be enhanced and the inhibitive efficiency greatly increased compared to solutions of the individual ions. Thus, synergistic inhibitive effects occur in such mixtures of anionic and cationic inhibitors . These synergistic effects are particularly well defined in solutions containing halide ions, I. Br , Cl", with other inhibitors such as quaternary ammonium cations , alkyl benzene pyridinium cations , and various types of amines . It seems likely that co-ordinate-bond interactions also play some part in these synergistic effects, particularly in the interaction of the halide ions with the metal surfaces and with some amines . 

BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric titration employs a cationic indicator to form a coloured complex with the surfactant which is insoluble in water but readily soluble in chlorinated solvents (1 ). The end point of the titration occurs when there is a loss of colour from the organic phase. A considerable improvement in this technique is achieved by the use of a mixture of anionic and cationic dyes (4 ), for example disulphine blue and dimidium bromide (Herring s indicator (3)). The sequence of colour changes which occurs during the two phase titration of an anionic surfactant (AS) with a cationic titrant (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) is summarised in Scheme 1 ... 

Chrisstoffels, L. A. J. de Jong, F. Reinhoudt, D. N. Sivelli, S. Gazzola, L. Casnati, A. Ungaro, R. Facilitated transport of hydrophilic salts by mixtures of anion and cation carriers and by ditopic carriers. J. Am. Chem. Soc. 

Bourrel M, Bernard D, Graciaa A (1984) Properties of binary mixtures of anionic and cationic surfactants Micellization and Microemulsions. Tenside Deterg 21 311-318... 

The application of COSMO-RS to the calculation of infinite-dilution activity coefficients in ionic liquids was surprisingly successful. As shown in Fig. 8.5, the activity coefficients of neutral compounds in ionic liquids are very well described. This was achieved without any special adjustment of COSMO-RS, which was developed and parameterized for neutral solvents, just by describing the ionic liquid as a 50 50 mixture of anions and cations. We only needed to take into account the convention of chemical engineers of counting a pair of an anion and a cation as... 

We will exclude from this review much discussion of the miscibility of low molecular weight polymers, where the miscibility is due primarily to a non-negligible entropy of mixing, except in cases where it helps to develop the ideas or relates to phenomena in high polymers. We will also exclude discussion of polymers which show strong complex formation such as in mixtures of anionic and cationic polyelectrolytes. 

The adsorption of mixtures of surfactants has received comparatively little attention. The adsorption of mixtures of nonionic and anionic surfactants has been studied (10,25-27) and strong negative deviations from ideality were observed (10,27). Attempts to model the degree of non-ideality using regular solution theory failed (21). The adsorption of mixtures of anionic and cationic surfactants would be expected to exibit even larger deviations from ideality (28). 

In another paper, the complication of multiple peaks in EKC was confirmed [23], The use of a preliminary ion exchange column was suggested to give only a single common cation or anion. This method preserves the use of pure water as the eluent but takes away the ability to separate mixtures of anions and cations simultaneously. 

Sol is passed through a bed containing a mixture of anion and cation exchange resins, simultaneously removing virtually all salts from the water. 

The mixtures of anionic and cationic surfactants are known to result in some association reaction that can be expressed as the equilibrium... 

Figure 18 Phase behavior of systems containing a mixture of anionic and cationic surfactants with oil, water, and alcohol. (From Ref 99.)...

As the IL is described by a binary mixture of anions and cations, the resulting j,cosMO-RS jg ternary value. The activity coefficient can be calculated at any molar concentration including infinite dilution. In case of infinite dilution and for univalent ions (applies for almost aU IL), the ternary value can be corrected to a binary value (which is also the result of the experiments) by Eq. (9.10). 

Anionic surfactants (such as sodium dodecyl sulfate), cationic surfactants (such as cetyltrimethylammonium bromide) (163), and nonionic surfactants (such as the polyoxyethylenated alkylphenols) (136,338) have been used in preparing emulsions. Different types of surfactants can be used in the same recipe (377) to provide additional stability under specific conditions. For example, mixtures of anionic and nonionic surfactants are common. The anionic surfactant controls the particle nucleation stage, and the nonionic surfactant imparts additional electrolyte tolerance, mechanical shear stability (345), and freeze-thaw stability. Mixtures of anionic and cationic surfactants tend to coagulate and are to be avoided. 

Kaler EW, Herrington KL, Miller DD, Zasadzinski JAN (1992) In Kaler EW, Herrington KL, Miller DD, Zasadzinski JAN (eds) Phase Behavior of Aqueous Mixtures of Anionic and Cationic Surfactants Along a Dilution Path Kluwer Academic Publishers, Dordrecht, pp 571-577... 

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