Determination by potentiometric titration

A number of authors have described the potentiometric titration with sodium tetraphenylborate (TPB), NaB(C6H5)4, of the pseudocationic 

Interferences from other surfactants were not studied, but cationics and amphoterics in acid solution would be expected to interfere quantitatively. Inorganic cations that have insoluble tetraphenylborates would also be expected to interfere, perhaps quantitatively. Anionics would not be expected to interfere. 

Reagent. The reagent is 0.01 M sodium tetraphenylborate, pH adjusted to 9 by adding sodium hydroxide. This can be standardised by poten-tiometric titration against thallium (I) nitrate if desired, but must in any case be calibrated against a pure sample of the nonionic. 

Sensing electrode. Aluminium wire coated with a membrane by dipping repeatedly into a solution of 0.09 g PVC and 0.2 ml 2,4-dinitrophenyl octyl ether in 3 ml tetrahydrofuran (caution flammable toxic vapour) and allowing the solvent to evaporate between treatments. 

Reference electrode. Calomel or silver-silver chloride. 

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Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

For the primary stage (phosphoric) V) acid as a monoprotic acid), methyl orange, bromocresol green, or Congo red may be used as indicators. The secondary stage of phosphoric) V) acid is very weak (see acid Ka = 1 x 10 7 in Fig. 10.4) and the only suitable simple indicator is thymolphthalein (see Section 10.14) with phenolphthalein the error may be several per cent. A mixed indicator composed of phenolphthalein (3 parts) and 1-naphtholphthalein (1 part) is very satisfactory for the determination of the end point of phosphoric(V) acid as a diprotic acid (see Section 10.9). The experimental neutralisation curve of 50 mL of 0.1M phosphoric(V) acid with 0.1M potassium hydroxide, determined by potentiometric titration, is shown in Fig. 10.6. 

The secondary amine function of dobutamine hydrochloride may be determined by potentiometric titration with perchloric acid using glacial acetic acid as a nonaqueous solvent. Mercuric acetate is used to tie up the chloride ion. 

In order to verify Equation 15, one must determine the equilibrium concentrations of [SOH], [SOH ], [H+], and [A-]. The surface concentrations are determined by potentiometric titrations while solute concentrations are measured using standard analytical techniques (12). The surface potential ipo can be evaluated by using the following relation (4) ... 

The amount of potassium bromide remaining in the recrystallized potassium glycidate is determined by potentiometric titration using a silver electrode. 

The ion-exchange capacity (lEC) of the samples was determined by potentiometric titration of the SPS-H form solution (90% dimethyl formamide, 10% water) with sodium hydroxide. 

Bioprocesses incorporating more than one redox enzyme in an oxidative reaction system might involve, in the simplest case, two oxidizing enzymes coupled so that they act sequentially to effect two oxidation steps. A key issue in the development of such oxidative biocatalytic systems would be the determination of the values, for each enzyme involved, of the redox potentials. These can be determined by potentiometric titration using redox mediators (such as NADH) and techniques such as cyclic voltammetry or electrophoresis [44]. Knowledge of the redox potentials would facilitate the design and engineering of a process in which the two... 

Elemental composition H 5.04%, F 94.96%. The total acidity of an aqueous HF solution may be measured by titration with a standard solution of base using phenolphthalein or another suitable color indicator. Alternatively, the end point may be determined by potentiometric titration. The fluoride ion may be analyzed using a fluoride ion-selective electrode or by ion chromatography. The HF gas may be analyzed by GC/MS using a GC column having... 

The dissociation constants of brinzolamide were determined by potentiometric titration of the hydrochloride salt with 0.05N NaOH, with two ionizations being observed. The first pKa, attributed to the deprotonation of secondary ammonium moiety, was observed at 5.8 8. The second pKa, attributed to deprotonation of the sulfonamide group, was at 8.48. 

For incorporation of crown ethers and cryptates into the RTV encapsulant system as sodium and potassium ion scavengers, the total ionic contaminants must first precisely be determined. Atomic absorption is used to measure these ions in commercial silicone RTVs and silicone fluids. Values of "10 ppm for sodium and potassium were obtained in the best samples. Chloride level was determined by potentiometric titration of the silicone with AgN03. A quantity of ion trap (either crown ethers or cryptates) was then added to the RTV silicone encapsulant, and its molar concentration was equal to the combined sodium and potassium contaminant levels. 

To determine the amylose content of starch, the iodine reaction has been most commonly used because amylose and amylopectin have different abilities to bind iodine. The methods such as blue value (absorbance at 680 nm for starch-iodine complex using amylose and amylopectin standards), and potentiometric and amperometric titration have been used for more than 50 years. These procedures are based on the capacity of amylose to form helical inclusion complexes with iodine, which display a blue color characterized by a maximum absorption wavelength (kmax) above 620 nm. During the titration of starch with iodine solution, the amount (mg) of iodine bound to 100 mg of starch is determined. The value is defined as iodine-binding capacity or iodine affinity (lA). The amylose content is based on the iodine affinity of starch vs. purified linear fraction from the standard 100 mg pure linear amylose fraction has an iodine affinity of 19.5-21.0mg depending on amylose source. Amylopectin binds 0-1.2mg iodine per 100mg (Banks and Greenwood, 1975). The amylose content determined by potentiometric titration is considered an absolute amylose content if the sample is defatted before analysis. 

Dimethylquinoxaline has a pKa of 2.08, and thus in general +M-substitutents at the 6-position are found to increase basicity, and —M-substituents have the reverse effect. The basicities of a series of 2,3-disubstituted quinoxalines have also been determined by potentiometric titration.243... 

The pKa values of a series of conjugated acids of the arsonium ylides have been determined by potentiometric titration (73). A decrease in the basicity of the ylides with an increase in substituent electronegativity was observed. The effect of the substituents agrees well with the Hammett equation. Arsonium ylides are more basic (200-230 times) than the corresponding phosphonium compounds. 

D 4739 D 4742 Base Number Determination by Potentiometric Titration. Oxidation Stability of Gasoline Automotive Engine Oils by Thin Film Oxygen Uptake (TFOUT)... 

The pKa values of perhydropyridof 1,2-a]pyrazin-l -one, its 2-methyl derivative and their N-5 oxides were determined by potentiometric titration in a 4 1 mixture of 2-methoxyethanol and H20 (81BAP423).The partition coefficients of 3-substituted 2,3,4,4a,5,6-hexahydro-l//-pyrazino[l,2-a]-quinolines have been determined in water-l-octanol [80IJC(B)879],... 

The chloride content of the same aliquot used for total acidity was determined by potentiometric titration with 0.1N silver nitrate solution. 

The interaction of a cation with a neutral oxide group results in the release of a proton, while the association of an anion results in the adsorption of a proton. Accordingly, the formation of a negative site from a neutral site involves the release of a proton and the formation of a positive site involves the adsorption of a proton. Therefore, the titratable surface charge determined by potentiometric titration is a measure of both the formation of surface-ion complexes and the ionization of surface functional groups, and... 

This calculated surface charge successfully predicted the titra-table surface charge, as determined by potentiometric titration, of goethite in a seawater major-ion electrolyte (Figure 7). 

Chlorides were determined by potentiometric titrations performed on distilled water dilutions. Carbonates and bicarbonates were either determined by titration or by calculation from pH measurements. Sulfates were determined by the gravimetric method utilizing BaS04 precipitation. 

Characterization. Number-average molecular weights (M s) of the stripped oligomers were determined by potentiometric titration of the primary-amine end groups with 0.10 N HCl. 

Hypoiodite Content of Iodine Solutions in Alkaline Media > as Determined by Potentiometric Titration with, 0.1 N Arsenite Solution... 

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