Sampling suspensions measurement

Using the pKa and the estimated So, the DTT procedure simulates the entire titration curve before the assay commences. Figure 6.7 shows such a titration curve of propoxyphene. The simulated curve serves as a template for the instrument to collect individual pH measurements in the course of the titration. The pH domain containing precipitation is apparent from the simulation (filled points in Fig. 6.7). Titration of the sample suspension is done in the direction of dissolution (high to low pH in Fig. 6.7), eventually well past the point of complete dissolution (pH <7.3 in Fig. 6.7). The rate of dissolution of the solid, described by the classical Noyes-Whitney expression [37], depends on a number of factors, which the instrument takes into account. For example, the instrument slows down the rate of pH data taking as the point of complete dissolution approaches, where the time needed to dissolve additional solid substantially increases (between pH 9 and 7.3 in Fig. 6.7). Only after the precipitate completely dissolves, does the instalment collect the remainder of the data rapidly (unfilled circles in Fig. 6.7). Typically, 3-10 h is required for the entire equilibrium solubility data taking. The more insoluble the... 

Figure 6. Effects of preheating of sample suspensions at 98°C for 30 min on the in situ emission Mossbauer spectra of Sn-119 arising from pentavalent Sb-119 at the hematite/0.25 mol dm 3 LiCl solution interface (measurement at room temperature) (A1) Before heating, pH 6.6 and (A2) after heating, pH 7.9 (B1)...

Turbidity is caused by any solid material which is dissolved or suspended in a liquid. The intensity of light scattered by a sample is measured and compared with that measured for standard formazin suspensions, and expressed as nephelometric turbidity units (NTU). Colour is determined as the absorbance (measured spectrophotometrically at 400 nm) of the sample filtered through a 0.4S micron pore size membrane filter [12, 13]. 

In essence, aqueous titration of surface acidity is an ion-exchange process in which hydrated surface protons are replaced by other hydrated cations (e.g., Na+, NIV") during the course of the titration. The procedure is straightforward. It usually consists of the direct titration of an aqueous suspension of the sample of powdered solid with a dilute base (e.g., sodium hydroxide) to a neutral endpoint. Another commonly used procedure consists of noting the pH of an appropriate salt solution (e.g., ammonium acetate), adding the sample, and measuring the amount of di-... 

Acidity of solid samples was measured by means of potentiometric titration. A small quantity of 0.05 N n-butylamine in acetonitrile was added to a known mass of solid suspended in acetonitrile, and agitated for 3 h. Later, the suspension was titrated with the same amine solution at 0.05 ml/min. The electrode potential variation was measured with a digital pHmeter. 

Weight concentrations of the aqueous /3-FeOOH and a-Fe203 suspensions used in electro-optical and electrophoretic measurements are 4 X 10 3 and 10 3 g dm-3, respectively, and their conductivity is 2 X 10 s Sm Each sample suspension is sonicated at 22 kHz for 1 min before polymer addition. 

The possibility of flocculation in the high ionic strength of the sodium chloride solution was countered by frequent agitation of particle solutions and sonification of samples before measurements were taken. Stirring the suspension between sampling runs was done for the 140-/xm and 280-/xm apertures to prevent losses by sedimentation. The teletype output for successive runs on given samples showed losses or variations of less than 10%. 

Fig. 3 Representative EPR measurements of OJ and HO generated from PM samples (suspensions) in phosphate buffer (pH 7.4). a and b are for DEP, c and d for GEP, e for PM2.5, f washed DEP with methanol, g is a simulation of the spin-trapped radicals, h is the simulation for DMPO-OOH...

The concentration of the suspension was 4x10- g/1 in the electro-optic technique and 4x10 g/1 in the Malvern technique. The pH, unless otherwise specified was 5.5 and the ionic strength 10. Each sample suspension was sonica at 22 KHz for 3 min before the measurement was started. 

Gravity sedimentation is normally carried out by using the "Andreasen" pipette technique. In its simplest form, a suspension of approximately 0.1% by volume of particles is placed in a measuring cylinder, and a pipette used to withdraw 10 mL from a fixed depth below the surface. Such an apparatus is shown in Figure 2.31. The concentration of samples are measured and compared with the initial one. Since all the particles will settle at their terminal velocities, the ratio of the two concentrations is the fractional weight of parficles to have reached a depth of H cm. Excluded will be the particles with a diameter smaller than (Table 1.2) as given in the relationship ... 

The hydrodynamic particle size distribution of samples was measured by dynamic light scattering (DLS-700, Otsuka Electronics) for the sample-redispersed aqueous suspension containing a small amount of sodium dodecyl sulphate as a dispersion stabilizer. The... 

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