Ionic suppression

In most cases, the swelling of polyelectrolyte hydrogels depends only on ionic strength of the solution but not on the size and nature of the ions [101]. Therefore, the ionic suppression curves similar to those of Fig. 2 and 3 are to some extent universal and allow to predict quantitatively the swelling of hydrogels for practically any ionic situation. 

The chromatographic technique of ionic suppression involves the use of a mobile phase which reduces the charge carried by the analyte. 

While the technique of ionic suppression (or ionization control) is only effective with weakly ionic species, ion-pair chromatography has been developed for strongly ionic species and again utilizes reverse-phase chromatography. If the pH of the solvent is such that the solute molecules are in the ionized state and if an ion (the counter-ion) with an opposite charge to the test ion is incorporated in the solvent, the two ions will associate on the basis of their opposite charges. If the counter-ion has a non-polar chain or tail, the ion-pair so produced will show significant affinity for the non-polar stationary phase. 

Matrix effects ionic suppression or enhancement in MS spectrometry... 

Acetic acid is used in the mobile phase to eliminate tailing of the peaks due to interaction with the residual silica active sites. This technique is referred to as ionic suppression since it also suppresses the ionization of the sample components. 

The drawbacks of ionic suppression and ion exchange chromatography led to the development of ion-pair chromatography (IRC)—an intriguing mode of HPLC that allows the separation of complex mixtures of polar, ionic, and ionogenic species. IPC is now an established and valuable separation strategy. 

Two basic approaches have been described to enhance the affinity of ionic compounds for the stationary phase in reversed-phase systems. The first approach, sometimes inappropriately referred to as ionic suppression involves the adjustment of the pH mobile phase so that the compound of interest is in the neutral or unionized form. The second approach to enhance the retention of ionic compounds on reversed-phase supports involves the application of ion-pair extraction techniques. 

The separation of ionic solutes may be performed by ionic suppression. Thus, carboxylic acids can be separated as non-ionized molecules by using an acidified... 

The ion suppression technique can be used to great effect for the analysis of weak acids or bases. For the analysis of acidic compounds the technique consists of the addition of a small amount of acetic or phosphoric acid to the mobile phase. By reducing the eluant pH dissociation of the sample molecules is suppressed. They thus have decreased affinity for the eluant and are retained to a greater extent by the ODS phase. The range of BPC is considerably extended using techniques such as ionic suppression and this mode of LC using ODS bonded phases finds wide application. 

FIGURE 46.41. Schematic illustration of ionic suppression of intergrain hopping. Compensation by cations of charge of acceptors removes the nearby localiz states on the polymer backbone that provide for holes easy hopping of electrons between grains. Reprinted from Ref. [235] > (2005) with permission from Elsevier. 

Suber, R.L. Edds, G.T. High performance hquid chromatographic determinations of sulfonamides by ionic suppression, J.Liq.Chromatogr., 1980, 3, 257-268. [for sulfanUtunide sulfaguanidine sulfamer-azine sulfamethazine sulfap5rridine sulfisoxazole JV-acetylsulfisoxazole sulfathiazole in plasma]... 

The difficulty in separating acid chlorophylls has prompted considerable effort. To improve resolution of the dephytylated chlorophyll derivatives, ionic suppressing reagents have been added to the mobile phase. These include ammonium and tetrabutylammonium salts [82,237], acetic acid [21,190], and 0.005 M NaCl [215]. Mantoura and Llewellyn [82] include the ionic reagent in both the sample and in the mobile phase to obtain a good resolution of chlorophyUides and pheophorbides. This method enables qualitative and quantitative monitoring of numerous chlorophyll derivatives and carotenoids in acetone extracts of algas from both cultures and natural waters. 

A wide variety of physical properties are important in the evaluation of ionic liquids (ILs) for potential use in industrial processes. These include pure component properties such as density, isothermal compressibility, volume expansivity, viscosity, heat capacity, and thermal conductivity. However, a wide variety of mixture properties are also important, the most vital of these being the phase behavior of ionic liquids with other compounds. Knowledge of the phase behavior of ionic liquids with gases, liquids, and solids is necessary to assess the feasibility of their use for reactions, separations, and materials processing. Even from the limited data currently available, it is clear that the cation, the substituents on the cation, and the anion can be chosen to enhance or suppress the solubility of ionic liquids in other compounds and the solubility of other compounds in the ionic liquids. For instance, an increase in allcyl chain length decreases the mutual solubility with water, but some anions ([BFJ , for example) can increase mutual solubility with water (compared to [PFg] , for instance) [1-3]. While many mixture properties and many types of phase behavior are important, we focus here on the solubility of gases in room temperature IFs. 

Anodic passivation also allows titanium to be employed as a Jig for aluminium anodising baths ", because the protective anodic film formed on titanium allows passage of electronic current to the metal contact while virtually suppressing flow of ionic current through the anodically-formed surface film. This aspect is discussed in more detail in relation to special applications. 

Ionic strength adjuster buffer 565, 570 Ionisation constants of indicators, 262, (T) 265 of acids and bases, (T) 832, 833, 834 see also Dissociation constants Ionisation suppressant 793 Iron(II), D. of by cerium(IV) ion, (cm) 546 by cerium(IV) sulphate, (ti) 382 by potassium dichromate, (ti) 376 by potassium permanganate, (ti) 368 see also under Iron... 

However, even if electrolytes have sufficiently large voltage windows, their components may not be stable (at least ki-netically) with lithium metal for example, acetonitrile shows very large voltage windows with various salts, but is polymerized at deposited lithium if this reaction is not suppressed by additives, such as S02 which forms a protective ionically conductive layer on the lithium surface. Nonetheless, electrochemical stability ranges from CV experiments may be used to choose useful electrolytes. 

The salt attack is also an important factor determining the SAH efficiency in the soil medium. In terms of Eq. (4.3), it is manifested by a sharp decrease of the coefficients y and B. The hydrogel structure prediction for specific application conditions requires to take into account universal (ionic strength) and specific (collapse) suppression phenomena and, therefore, a rather delicate balancing in search for a compromise between swelling gains due to the network density (n ) and the ionicity ((3). 

Antiarrhythmic drugs are substances that affect cardiac ionic channels or receptors, thereby altering the cardiac action potential or its generation or propagation. This results in changes of the spread of activation or the pattern of repolarization. Thereby, these drugs suppress cardiac arrhythmia. 

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