PH method

It may be noted that very weak acids, such as boric acid and phenol, which cannot be titrated potentiometrically in aqueous solution, can be titrated conductimetrically with relative ease. Mixtures of certain acids can be titrated more accurately by conductimetric than by potentiometric (pH) methods. Thus mixtures of hydrochloric acid (or any other strong acid) and acetic (ethanoic) acid (or any other weak acid of comparable strength) can be titrated with a weak base (e.g. aqueous ammonia) or with a strong base (e.g. sodium hydroxide) reasonably satisfactory end points are obtained. 

Samples without Interfering Materials Single pH Method...483... 

The pH differential method was described as a fast and convenient assay for the quantitation of monomeric anthocyanins by Giusti (2001). It was approved by the Association of OfQcial Analytical Chemists (AOAC) in 2005 as a standard method to evaluate total monomeric anthocyanin pigment content in fruit juices, beverages, natural colorants, and wines. The degradation index is the ratio between total and monomeric anthocyanins (Table 6.3.1). The content of total anthocyanins can be obtained by the single pH method and the monomeric anthocyanin by the pH differential method. ... 

Avdeef, A., Berger, C. M., Brownell, C. pH-metric solubility. 2. Correlation between the acid-base titration and the saturation shake-flask solubility-pH methods. Pharm. Res. 2000, 17, 85-89. 

Several approaches for higher-throughput lipophilicity measurements have been developed in the pharmaceutical industry [38], including automated shake-plate methods [46], and some of these are now available commercially [47]. A convenient method to measure octanol/water partitioning is based on potentiometric titration this is called the pH-method [48],... 

To illustrate the subtle differences between the iso-pH and gradient-pH methods, ketoprofen was used in a series of simulation calculations. Figure 3.5a shows the concentration-time profiles for ketoprofen under an iso-pH condition. Consider the case of iso-pH 3, where the molecule is essentially uncharged in solution (pKa... 

Now consider the gradient-pH case, with pHD 3 and pHa 7.4. In Fig. 3.5b, the dashed curve (donor concentration) corresponding to pH 3 decreases more steeply after the retention period than that of the previous iso-pH example. Furthermore, there is not the large initial drop due to the disappearance of the sample into the membrane in the gradient-pH case, retention drops from 56% to 9%. Thus, more of the compound is available for sample concentration determination. The solid curve (acceptor concentration) corresponding to pH 3 also grows more rapidly than in the iso-pH example. The dashed and solid curves cross at 7 h, with C(t)/CD(0) close to the 0.5 value. Note also, that about 70% of the compound ends up in the acceptor well at the end of 16 h - much higher than is possible with the iso-pH method. 

The Langmuir-Blodgett method has been used to prepare hybrid films of an anionic Ru(ll) cyanide polypyridyl complex with LDHs [170]. An LDH film was formed on mica owing to the interaction between LDHs particles and the Ru(ll) cyanide polypyridyl complex that was pre-dispersed on the surface of mica. Water-in-oU emulsions composed of octane, water and sodium dodecyl sulfate (SDS) have been used to synthesize Mg/Al LDHs with carbonate as the interlayer anion [171] by constant pH or variable pH methods. A floccule or fiber-like LDH material that possesses similar chemical composition and properties to that synthesized using a conventional variable pH method was obtained. The resulting LDH shows high surface area and a narrow distribution of mesopores. 

For quantitative detn of acidity two methods can be used a) If the sample melts below 100°(such as TNT, DNT, etc) shake it with boiling neutral w, cool, filter the extract and titrate it with std alkali (such as 0.05N NaOH) in presence of an indicator or det the pH of the extract b)If the sample melts above 100° (such as RDX) or does not melt at all (such as NQ, dissolve it in neutral acet, add neutral w to reppt the sample, filter the slurry and det the acidity of filtrate either by titration with std alkali or by the pH method... 

Organic compound Rate constant, M 1 s 1 pH Method Reference no. 

Procedure. The direct pH method described previously was used to determine the stability constants (13). The solutions used had a ligand to metal ratio of about 2 1 and the concentration level was about O.OOIM rare earth ion. All solutions were made up to ionic strength O.IM using potassium nitrate. Experimental data for one system are given in Table I. 

The physical and chemical properties of precipitated particles can be tailored by the precipitation conditions such as solution concentration, precipitation temperature, pH, method of addition, and mixing intensity. The adjustment of these conditions can be achieved by using equipment with a setup similar to that depicted in Fig. 3. The parameters most often... 

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