IEP, isoelectric point

Figure V-8 illustrates that there can be a pH of zero potential interpreted as the point of zero charge at the shear plane this is called the isoelectric point (iep). Because of specific ion and Stem layer adsorption, the iep is not necessarily the point of zero surface charge (pzc) at the particle surface. An example of this occurs in a recent study of zircon (ZrSi04), where the pzc measured by titration of natural zircon is 5.9 0.1...

Isoelectric point (IEP), 20 479 Isoelectronic point, 3 674 selected inorganic particles,... 

The isoelectric point (IEP(s)) and the zero point of charge (ZPC) are convenient references for predicting the charge-dependent behavior of oxide minerals and their suspensions. 

The concentration of potential-determining ions at which the zeta potential is zero (C = 0) is called the isoelectric point (iep). The isoelectric point is determined by electrokinetic measurements. We have to distinguish it from the point of zero charge (pzc). At the point of zero charge the surface charge is zero. The zeta potential refers to the hydrodynamic interface while the surface charge is defined for the solid-liquid interface. 

The different situations of the block copolyampholyte as a function of pH are depicted in Scheme. 1. The same order of deprotonation was observed in copolymers of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) [70, 71, 72, 75-77]. In copolymers of poly(methacrylic acid) [78] and poly(2/4-vinylpyridine), on the other hand, deprotonation of the pyridine hydrochloride takes place prior to deprotonation of the carboxyl [79-83] because in comparison to carboxylic functionalities amine hydrochlorides are the weaker acids and vinylpyridinium hydrochlorides the stronger ones. Thus, in the latter systems an isoelectric point (iep) is not observable, while in the first case polyzwitterions are formed which possess the highest amount of charges at that pH resulting in a polyelectrolyte complex (PEC). In the second case polymers with a minimal net charge built the PEC which is stabilized by hydrophobic interactions often accompanied by hydrogen bonding [79, 84-88]. 

A chemical structure having both anionic and cationic charges on the same molecule is called a zwitterion. At a specific pH, the degree of the ionization of the zwitterion to an anionic electrolyte or to a cationic electrolyte is the same. The pH is called the isoelectric point (IEP). At the IEP, the same amount of anionic and cationic electrolytes exist. The zwitterion has the lowest solubility, denoted as SG. One can write the ionization of an ampholyte simply as ... 

Figure 2.13 shows the fractional equilibrium concentration curves for serine (pKal = 2.2 and pKa2 = 9.22). One can use the same equations, Equation (2.107a), Equation (2.107b), and Equation (2.107c), if H2A, HA, and A-2 are substituted by HY+, HY1, and Y, respectively. The isoelectric point (IEP) is the pH at which the amino acid does not move in an electrical field or possesses a net charge of zero. It is obtained from (pKal + pKa2). 

The pH of a solution influences the extent of adsorption. The majority of pharmaceutically active drugs are weak acids or weak bases. The degree of ionization and solubility of the adsorbate drug molecule are dependent on pH. As described above, more ionized (i.e., polar) and soluble adsorbates adsorb much less than their unionized forms (i.e., lypophilic) do. For amphoteric adsorbates, a maximum adsorption capacity occurs at the isoelectric point (IEP), where the net charge of the adsorbate becomes zero, and at the lowest solubility. In general, pH and solubility... 

To investigate the chemical functionality or the order of deprotection of the photoresist surface, the zeta potential of some chosen photoresist samples was measured in electrolyte solutions as a function of the pH value. It is shown in Fig. 6. In consequence of dissociation and adsorption processes at the surface the zeta potential decreases monotonically. The pH value at which the zeta potential function passes zero is called the isoelectric point (iep). Figure 4c shows the iep as a function of the exposure dose. It is shifted to smaller values if the exposure dose approaches the threshold value. This is caused by the generation of acid groups at the surface during processing (cf. Scheme 1). In the case of unexposed photoresist no functional groups exist at the surface. Ion adsorption processes... 

Fig. 6 Zeta potential of flat photoresist layers processed with various exposure doses 0% (squares), 79% (circles), 100% (triangles), 104% (diamonds) of the threshold dose as a function of the pH value, measured in 10-3 M KC1. The arrows mark the isoelectric point (iep) for the lowest and highest exposure dose...

The results obtained proved that very good correlations exist between the value of electrokinetic potential, HPLC results, XPS measurements, contact angle values and changes in the isoelectric point (IEP). 

Also, the enzymatic treatment causes a change in the isoelectric point (IEP) value of wool, as demonstrated by the electrokinetic measurements (Fig. 5). With an increase in enzyme concentration the IEP value shifts in the direction of more acidic pH (from 3.8 for untreated wool to 3.7 for wool after 1% enzymatic treatment, and 3.45 for wool... 

On strictly electrostatic basis, the E. coli abatement should be much less favored at pH 8.5 than at pH values of 4.5 and 6.0, since E. coli is negatively charged between pH 3 and pH 9, and Ti02 Degussa P-25 surface becomes more positively charged up to pH 7.0, because the isoelectric point (IEP) is 6.5. However, this was... 

The adsorption behavior of weak polyampholytes from aqueous solutions on to a solid wall is strongly determined by the pH of the polymer solution. So it is absolutely necessary to investigate the adsorption as function of pH. As an example the adsorbed amount of two polyampholytes with medium molecular weight of around 60,000 g mol-1 and different block sizes is shown in Fig. 14 [13]. In every case the isoelectric point IEP of the polymer, which is determined by the block ratio, is the prominent feature of adsorp-... 

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