Measurement centrifuging method

BS W Bottoms, Sediment, and Water. This centrifuge method is used to measure the approximate amount of suspended solids and water in crude oil and petroleum products. 

Jaurequi, C.A., Regenstein, J.M., and Baker, R.C. 1981. A simple centrifugal method for measuring expressible moisture A water-binding property of muscle foods. J. Food Sci. 46 1271 -1273. 

Some of the disadvantages were overcome by the use of the colloidal probe technique to measure adhesion forces (review Ref. [216]). The colloidal probe technique offers the advantage that the same particle can be used for a series of experiments and its surface can be examined afterwards. The accessible range of particle size is typically limited to a range between 1 /zm and 50 pm. The tedious sample preparation, limits the number of different particles used within one study, for practical reasons. Therefore the colloidal probe and centrifugal methods complement each other. 

Experimental Procedure. A dispersion of fat crystals in oil was obtained by adding 5 mL of the preprepared oil solution (saturated by -PPP, as above), to a controlled amount of unlabeled PPP crystals (either 10 or 20 mg). TTie polymorphic form of the PPP crystals was determined to be P [from diff ential scanning calorimetry (DSC)]. The dispersion was gently agitated and the temperature controlled at the temperature of interest. At regular intervals, a sample (ISO pL) of the dispersion was removed and centrifuged. The clear upper phase of this sample was then analyzed by the detector, and so the residual -PPP in the oil at that time was measured. The method is further described in a [nevious pr r. 

Water and sediment in petroleum can be determined simultaneously (ASTM D-96, ASTM D-4007, IP 359) by the centrifuge method. Known volumes of petroleum and solvent are placed in a centrifuge tube and heated to 60°C (140°F). After centrifugation, the volume of the sediment-and-water layer at the bottom of the tube is read. For petroleum that contains wax, a temperature of 71°C (160°F) or higher may be required to completely melt the wax crystals so that they are not measured as sediment. 

The most significant advance in particle size distribution measurement in the submicrometer particle size region has been the development of field-flow fractionation methods [2] over the past 15 years. These methods have been applied successfully to colloidal silica. The methods separate the particles according to size so that an actual distribution is measiued. The smallest particles are measured first Dilution of commercial sols is required for these measurements. Separation of particles is also effected by the disk centrifuge method, but in this case detection of small particles is time consmning and difficult to quantify. 

Capillary electrophoresis and ultra-centrifugation methods are also not sufficient due to poor reproducibility and the requirement for a large quantity of proteins, respectively. These are fundamental problems in protein-drug binding measurements. Reference log riRT values vary significantly, probably due to the different qualities of HSA and the different analytical systems used. 

Fig. 1. Changes in intracellular Cj pool (upper panels) and photosynthetic products (lower panels) of WT, RKb and M9 cells with incubation time in the light, measured by the silicone-oil centrifugation method., A high-C02 cells 0,A cells exposed to low CO2 for 20 h , 0 C09 (9.9 /z M, final concentration) was added A, A 414m"...

One has to measure the force required to remove the partide from the substrate 11.16.2.1 Centrifugal Method (Krupp, 1967)... 

The LS measurements (static method) were performed on a FICA 42000 photogoniometer fitted with a He-Ne laser source of 4 mW at 632 nm wavelength, vertically polarized. Before these measurements the samples were centrifuged for 2 h at 14000 T/min. The refractive index increments were separately determined at the same wavelength using a BRICE-PHOENIX refractometer. 

The centrifugal method of measuring the value of the detaching force is the principal method used in determining forces of adhesion. The advantages of this method lie in its simplicity and accessibility, and also in the reliability of the results and the rapidity of the measurements. In addition to this, a variety of conditions may be created in the centrifuge test tubes (humidity, temperature, pressure, etc.), which widens the experimental potentialities of the method. However, in order to obtain the integral adhesion curve several measurements must be made with different numbers of revolutions. 

Results obtained by different methods of adhesion measurement (with the same materials and imder the same conditions) are similar. Thus, the adhesive forces for glass particles sticking to a metal surface (brass and steel) are approximately the same, despite differences in the method of detachment (vibration and centrifuging) the adhesive forces measured with a relative air humidity of 50-60%, using the centrifuge method to remove the glass particles, are the same as those obtained by the method of detaching individual particles. 

When the sedimentation process due to gravity is too slow for measurement of particle size, centrifugal forces can be imposed on the particles up to speeds of 100,000 rpm in an ultracentrifuge. The same light, acoustic, and x-ray techniques can be applied to centrifugal methods to note change in concentration and thus the particle size distribution. 

There are several techniques available for the measurement of the adhesion force of particles on substrates. These techniques involve both the study of individual particles (as in the microbalance technique) and of multiple particles by statistical counting (as in the centrifuge method). In each type of study the conditions of both the particles and the substrates must be known with high precision. The exact chemistry, physical size and shape, surface condition, temperature, and properties of the surrounding gas are vital parameters that must be quantified in order to obtain reproducibility. 

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