Natural particles, electrophoretic

Fig. 5. Plot of the logarithm of the electrophoretic mobility of natural particles in the Gironde, Loire and Conwy estuaries (Date for Conwy from Hunter and Liss, 1982).

Figure 4. Variation of electrophoretic mobilities of natural particles with salinity of the medium. Standard deviations are indicated. Data...

The coefficient of variation of electrophoretic mobilities in the case of natural particles (33%) was greater than that found for immersed test particles all of a single kind in natural water (< 10% ). However, the range of mobilities spanned by the entire population of many kinds of test particles in natural water is quite similar to that found with the natural particles shown in Figure 3. 

A number of methods for the determination of electrophoretic velocity and electrokinetic potential of particles have been developed. These methods include the moving boundary method (a direct study of motion of the boundary between the disperse system and the free dispersion medium due to the applied potential difference), microelectrophoresis (a direct observation of moving particles using a microscope or ultramicroscope), electrophoresis in gels, paper electrophoresis, etc [ 13]. These methods are broadly used to study disperse systems formed with low molecular weight substances, as well as polymers, especially those of natural origin. Electrophoretic methods allow one to separate and analyze mixtures of proteins, and thus are effectively used in scientific research and medical diagnostic applications. 

The Penn State workplan is based on five tasks Task 1 to participate in round-robin particle electrophoretic mobility measurements, Task 2 to determine the nature of reactive sites on the silicon nitride surface, Task 3 to modify the chemistry of the silicon nitride interface using organic species, Task 4 to determine the rheological and dispersion properties of the nonaqueous silicon nitride suspensions, and Task 5 to ensure transfer technology to ORNL via meetings and reports. Each task is discussed in detail below. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

An important technique for the qualitative and quantitative analysis of different macromolecular materiafs is based on the efectrophoretic separation of particfes having different transport vefocities (e.g., because they have different zeta potentiafs). This technique is used for the anafysis of proteins, pofysaccharides, and other naturally occurring substances whose molecular size approaches that of colloidal particles (for more details, see Section 30.3.4). It is an advantage of the electrophoretic method that mild experimental conditions can be used—dilute solutions with pH values around 7, room temperature, and so on—which are not destructive to the biological macromolecules. 

The electrophoretic mobility of natural suspended sediments has been measured on the field a few hours after sampling using a Pen Kern s Model 501 Laser Zee Meter which uses a rotating prism design enabling simultaneous measurements of many particles. 

Model particle mobility has been determinated with the Tiselius method (Tiselius, 1937, 1938). This method also allows the integration of the mobility of a large number of particles even if the refractive index is very close to that of the electrolyte medium, allowing to minimize the experimental errors inherent to the classical microelectrophoretic techniques. The electrophoretic mobilities will not be transformed into surface charges because the theoretical relationship between these parameters is highly dependant on the particle radius of curvature and the electrolyte concentration in the vicinity of the particle (Hunter and Wright, 1971). For both methods, the analytical error falls below 5 %, however, it increases up to 10 % for natural composite samples and/or low mobilities. 

We have tried to specify the influence of different physico-chemical parameters upon the electrophoretic mobility, using model particles such as silica (Aerosil 380 - Degussa) which is characterized by a charge very close to that of natural suspended sediment from Loire and Gironde. 

Fig. 4. Electrophoretic mobilities (Ug)of natural (untreated) - curve A - and treated particles as a function of salinity (S°/°<>) for two sets of samples from Keithing Burn (KB 1 open symbols - 31 March 1982 KB 2 closed symbols - 30 dune 1982). Shaded area B indicates the spread of results from other estuaries (redrawn from Fig. 3 of Hunter and Liss 1979). Curve D - suspended particles centrifuged and resuspended in UV- oxidized sample supernatant and then UV-oxidized. Curve C - natural samples (particles plus supernatant) UV-oxidized. Curve E - sample supernatant UV-oxidized to form new particles (UV-PPT). Several UV-PPT samples from KB2 were centrifuged and the particles resuspended in their original untreated sample supernatant. The resulting changes in Ug are indicated by the dashed lines (asterisks - final values). Keithing Burn suspended matter is mostly composed of iron oxides (after Loder and Liss, 1985).

Electrophoresis plays a key role as an analytical or preparative technique in the characterization of natural organic matter because it gives information about the behavior of these molecular mixtures in controlled solution conditions, depending on both the size and the charge distribution frequency of the analytes in the complex mixture. Historically, the first electrophoretic separations were conducted with environmental colloids and over the years all the techniques based on zone, gel electrophoresis, or isoelectric focusing were used in their different setups to analyze natural organic matter and environmental particles to a minor extent. The goal of... 

Most electrophoresis experiments are carried out mlcro-electrophoretically and hence with very dilute sols. When the sols are not so dilute, particle-particle interaction may occur and this may influence the mobility. The interaction has a two fold nature electrostatic and hydrodynamic. Electrostatic interaction is of the range 0(x ), whereas the hydrodynamic interference is 0(aj. For most systems it means that the latter predominates. Because of this, interaction... 

Figure 2. Electrophoretic mobilities of particles in seven4on (l t) and natural sea water (right). Tie lines connect values for the same kind of particle. Data from Ref. 15.

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