Isoelectric point defined

All ions in the system, whether specifically adsorbed or not, must be expected to saturate partially the ion exchange capacity arising from these relatively pH-independent sources. For this reason an isoelectric point defined in terms of hydrogen and hydroxyl ion adsorption is hypothetical, and in any real system, the pH at which zero surface charge is observed will depend upon the system composition. 

At the isoelectric point, the acid dissociation equals the base dissociation. The degrees of dissociation ocx and oc2 are defined in such a way that... 

A very important property of proteins is the isoelectric point. This is defined as the point at which the total negative and positive charges on the molecule are balanced. This point is where it is easiest to precipitate the protein. By analogy with the pH scale the isoelectric point is written pi. 

Both isoelectric albumin and its undissociated acid and basic salts are less solvated and imbibe less liquid than the ionised form thus the viscosity of an albumin solution will be least at the isoelectric point rising to more or less well defined maxima on each side, these maxima coinciding with the points of maximum dis-... 

The isoelectric point may be conveniently defined as the ZPC expected for a pure, single component solid oxide, hydrous oxide, or hydroxide with a nondefective structure in an electrolyte totally devoid of specifically adsorbed polar or ionic species. An IEP(s) can be calculated from the charge and size of the cation using Equation 13 and the constants in Tables I and II. The maximum accuracy to be expected may be judged from the graphical correlation given in Figure 3. 

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 ZPC of a solid is the pH of an aqueous solution in contact with the solid when the solid has a net surface charge of zero. The ZPC depends on the composition of the solid and the concentration and chemistry of the electrolytes in the aqueous solution. In situations where surface charges are only controlled by the adsorption of OH- or H+, the ZPC is the isoelectric point (Faure, 1998), 218-219 (Langmuir, 1997), 350 (Drever, 1997), 93. Unfortunately, isoelectric points and ZPCs are not consistently defined or utilized in the literature. That is, some authors refer to the isoelectric point of particular solid sample when they are actually referring to its ZPC as the term is defined in this chapter. 

Two important parameters describing the EDL of a mineral are the point of zero charge (PZC) and the isoelectric point (IP). Healy et al.18) define the PZC as the concentration of PDI with the surface charge of a mineral metal oxides, PZC is determined by the concentration of PDI H+ or OH", in sparingly soluble salts by the concentration of PDI of the lattice. When both mechanisms of surface charge formation operate simultaneously, both ion species and their reaction products determine the PZC16,31). The IP is defined18) as the concentration of PDI at which the electrokinetic potential = 0. 

The main characteristics of amphoteric surfactants is their dependence on the pH of the solution in which they are dissolved. In acid solutions, the molecule acquires a positive charge and it behaves like a cationic, whereas in alkaline solutions they become negatively charged and behave like an anionic. A specific pH can be defined at which both ionic groups show equal ionization (the isoelectric point of the molecule). 

A very important property of proteins is the isoelectric point. This is defined as the point at which the total negative and positive charges on... 

This association is greatest at the isoelectric point of the protein and being readily dissociated at pH s above or below the isoelectric point ( iJ.) Phytate association in cereal grains is less well defined but is contained in significant concentrations both in the bran and germ (12). There appears to be at least one ferric ion associated in the otherwise soluble phytate complex in wheat bran (13). Phytate in sesame seed appears to be the most unique and least soluble of all seeds. In this case magnesium appears to be the predominant cation (9 ) ... 

The isoelectric point (lEP) is defined as the pH value at which reverses its sign. As is seen from Eq. (4.117), lEP depends on the electrolyte concentration n. 

Isoelectric Point (pH) The isoelectric point (lEP) is defined as the pH at which the abrasive surface is charge neutral. The role of lEP in determining CMP behavior of glasses has been documented several times in the past (see Chapter 4). The importance of this concept in polishing metals needs to be established, possibly assuming that the metal surface is passivated to form an insulating layer on the surface, which is then removed by abrasion. 

The isoelectric point (lEP), a characteristic property of proteins, is defined as the pH where the electrokinetic potential is zero or that pH where no migration occurs in an electric field 2, 3, 4). For gelatins the... 

This is often referred to as the isoelectric point. It is the condition where particles do not move in an applied electric field. If one wants to specify that the pzc is established solely due to binding of or OH", one may specify point of zero net proton charge (or condition) (pznpc). Furthermore we can define a point of zero salt effect (pzse)... 

The pH value at which the oxide surface carries no fixed charge, i.e. Oj = 0, is defined as the point of zero charge (PZC) . A closely related parameter, the isoelectric point (lEP), obtained from electrophoretic mobility and streaming potential data, refers to the pH value at which the electrokinetic potential equals to zero The PZC and lEP should coincide when there is no specific adsorption in the iimer region of the electric double layer at the oxide-solution interface. In the presence of the specific adsorption, the PZC and lEP values move in opposite directions as the concentration of supporting electrolyte is increased. ... 

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