Mass titration method

Recently two methods applicable in low ionic strength conditions were developed (i) the mass titration method [38,39], and (ii) the adhesion method for solving the problem of sample conductivity [40-42]. 

The mass titration method is based on work by Noh and Schwarz who showed that addition of an oxide powder to an electrolyte solution changes the pH to a constant value which corresponds to the point of zero charge [38]. The method was experimentally and... 

Reaction enthalpies obtained from the temperature dependency of the pzc axe standard values corresponding to dilute systems. Figure 6. displays the results with hematite obtained by the mass titration method, which is suitable because of its applicability at low ionic strength. 

The potentiometric mass titration method [657,658] produces results equivalent to those of the drift method described above. The same amount of base is added to three dispersions with different solid-to-liquid ratios and a constant ionic strength. The dispersions are titrated with acid, and the pH is recorded as a function of the amount of acid added. The intersection point of the obtained curves is taken as the PZC. In other words, the PZC is identified with the pH at which solid addition does not induce a change in pH. The drift method and mass titration are based on the same principle, the difference being that in potentiometric mass titration, the reagents are added in a different order. Potentiometric mass titration is affected by the acid or base associated with the powder in the same way as in the drift method and mass titration. The advantage of potentiometric mass titration over the drift method is that in the former the pH is measured only in buffered systems. 

In the mass titration method, the PZC is determined as the natnral pH of a concentrated dispersion. A detailed description of the experimental procedure can be found in [667], Mass titration become popular in the late 1980s [668,669], but the same method was already known in the 1960s as the pH drift method [183], Usually, a series of natural pH values of dispersions with increasing solid loads is reported, but only the natural pH of the most concentrated dispersion is actually used. The only role of the data points obtained at lower solid loads is to confirm that a plateau was reached in pH as a function of solid load that is, a further increase in the solid load is unlikely to bring about a change in pH. The mass titration method is based on the assumption that the solid does not contain acid, base, or other surface-active impurities. This is seldom the case, thus mass titration often produces erroneous PZCs. In this respect mass titration is similar to the potentiometric titration without correction illustrated in Figure 2.7, only the solid-to-liquid ratio is different. The experimental conditions in mass titration (solid-to-liquid ratio, time of equilibration, nature and concentration of electrolyte, and initial pH) can vary, but little attention has been paid to the possible effects of experimental conditions on the apparent PZC. The effect of an acid or base associated with solid particles on the course of mass titration was studied in [670], To this end, a series of artificially contaminated samples was prepared by the addition of an acid or base to a commercial powder. The apparent PZC of silicon nitride obtained in [671] by mass titration varied from 4.2 (extrapolated to zero time of equilibration) to 8.2 for time of equilibration longer than 20 days. The method termed mass titration was used in [672], but it was different from the method discussed above. 

For either of the ternary complex mechanisms described above, titration of one substrate at several fixed concentrations of the second substrate yields a pattern of intersecting lines when presented as a double reciprocal plot. Hence, without knowing the mechanism from prior studies, one can not distinguish between the two ternary complex mechanisms presented here on the basis of substrate titrations alone. In contrast, the data for a double-displacement reaction yields a series of parallel lines in the double reciprocal plot (Figure 2.15). Hence it is often easy to distinguish a double-displacement mechanism from a ternary complex mechanism in this way. Also it is often possible to run the first half of the reaction in the absence of the second substrate. Formation of the first product is then evidence in favor of a doubledisplacement mechanism (however, some caution must be exercised here, because other mechanistic explanations for such data can be invoked see Segel, 1975, for more information). For some double-displacement mechanisms the intermediate E-X complex is sufficiently stable to be isolated and identified by chemical and/or mass spectroscopic methods. In these favorable cases the identification of such a covalent E-X intermediate is verification of the reaction mechanism. 

Another key contribution of the Schwarz group was the recognition of the dramatic influence of oxide surfaces on bulk solution pH. In a landmark 1989 paper, Noh and Schwarz [7] demonstrated the method of mass titration, in which successive additions of oxide cause stepwise shifts in solution pH. This procedure is illustrated in Figure 6.7 [7], As indicated in Figure 6.1, the protonation-deprotonation chemistry of the surface hydroxyl groups is coupled to the liquid-phase pH. In mass titration, as the mass (or more appropriately, the surface area) of oxide in solution increases, the solution pH is brought to the PZC of the oxide, at which point no driving force for proton transfer exists... 

The bomb method for sulfur determination (ASTM D129) uses sample combustion in oxygen and conversion of the sulfur to barium sulfate, which is determined by mass. This method is suitable for samples containing 0.1 to 5.0% w/w sulfur and can be used for most low-volatility petroleum products. Elements that produce residues insoluble in hydrochloric acid interfere with this method this includes aluminum, calcium, iron, lead, and silicon, plus minerals such as asbestos, mica, and silica, and an alternative method (ASTM D1552) is preferred. This method describes three procedures the sample is first pyrolyzed in either an induction furnace or a resistance furnace the sulfur is then converted to sulfur dioxide, and the sulfur dioxide is either titrated with potassium iodate-starch reagent or is analyzed by infrared spectroscopy. This method is generally suitable for samples containing from 0.06 to 8.0% w/w sulfur that distill at temperatures above 177°C (351°F). 

Dialkyl peroxides (continued) colorimetry, 707-8 flame ionization detection, 708 NMR spectroscopy, 708 titration methods, 707 UV-visible spectrophotometry, 707-8 enthalpies of reactions, 153-4 graft polymerization initiation, 706 hydroperoxide determination, 685 peroxide transfer synthesis, 824-5 stmctural characterization, 708-16 electrochemical analysis, 715-16 electron diffraction, 713 mass spectrometry, 714 NMR spectroscopy, 709-11 thermal analysis, 714-15 vibrational spectra, 713-14 X-ray crystallography, 711-13 synthesis... 

The materials were dried in a vacuum oven at room temperature and then suspended in hexane solution for use as polymerization initiators. A GC-mass spectroscopic method was used to verify the purity of this material, and a titration (11) was used for the determination of total alkalinity. 

Stock solution. The concentration of the stock solution was determined by the sodium iodate-thiosulfate titration method. For each determination, a 100.0-ml solution was prepared and placed in a vessel connected to a manometer for measuring the pressure. The vessel was sealed after insertion of a measured piece of catalase-immobilized CoFoam. The reaction of catalase with peroxide produces O2, and an increase in pressure indicates a degradation of the peroxide. Thus, a change in pressure in the vessel is a measure of the reaction rate. Since it is sufficient to show differences in test samples, the ideal gas law was used to convert the pressure into mass. The barometer was calibrated with a gauge traceable to National Institutes of Standards and Technology (NIST) standards. 

Gravimetric titrimetry — A - titration method in which the mass of - titrant that is added to the - titrand is weighted by using a balance [i]. 

As the drying methods commonly used for the determination of the water content of powders do not selectively measure the water content, but rather the mass lost under specific drying conditions, the Karl Fischer titration method was used... 

We took a clear microemulsion sample of 0.22 water mass fraction near the phase boundary, first titrated with IPA till the sample just became turbid, then titrated with water till the sample became clear again. Repeating these procedures many times and plotting the ratio of Nw/Ng versus Na/Ng, we then obtained a straight line as shown in Figure 9. The slope yields the constant k and the intercept on y-axis corresponds to the minimum number of water molecules per surfactant molecule required for dissolution. It was concluded that minimum 8 water molecules are needed to hydrate each sulfate group for dissolution of SDS into IPA. It should be noted that this titration method can only be used in the miscibility range of the short chain alcohol with water. 

The method termed mass titration was originally described by Noh and Schwarz [59]. Dispersions containing 0.01, 0.1, 1,5, 10 and 20% of solid in deionized and outgased water are equilibrated for one day under nitrogen atmosphere. The pH is measured and plotted versus log (mass% of solid) and the plateau in the curve indicates the PZC. Addition of inert electrolyte was recommended (but not applied) in the original paper and the problem of optimum concentration of inert electrolyte was not addressed. The agreement between results obtained by mass titration and the CIP was good for alumina but problematic for titania. 

Although mass titration was originally designed as a method of determination of PZC, surface charging curves can also be calculated from mass titration data [60]. 

A completely different method is referred to as mass titration" in Ref. [64] Namely, a certain amount of powder is added to the solution of given pH and the dispersion is titrated with acid or base until the original pH value is reached. This procedure is very different from the mass titration discussed above, and it seems to be variation of potentiometric titration without correction for PZC = CIP, thus the results are reported as pH" in Table 3.1. 

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