Micro-Electrophoresis Apparatus Mk II
The Rank Brothers Micro-Electrophoresis Apparatus will determine the electrophoretic mobility of a wide range of suspended particles. It has a wide and established user base in all fields where flocculation, dispersion and surface adhesion are important parameters to control.
Picture of Micro-Electrophoresis Apparatus setup for electrophoretic mobility measurements using Pyrex cylindrical thin walled cell, especially suitable for:
- Very small particles (ultra-microscope conventional or laser illumination).
- High electrolyte concentration (small cross section, giving small currents and little polarisation).
- Rapid thermostatting and freedom from convection currents.
Physical and Biological Applications of Electrophoresis
The term electrophoresis refers to the motion of a charged particle when an electric field is applied. When the velocity of the particle is measured, by timing over a known distance, it is possible to calculate the electrical potential at the surface of shear between the particle and the surrounding medium and from this the electric charge contained within the surface of shear. When the particle is in a relative charge free medium, such as air or a low dielectric constant liquid, it becomes convenient to calculate the charge directly. Careful consideration must be given to whether the charge is an equilibrium property of the particle or whether it is an accidental property determined by the history of the particle and what it happens to have collided with. However in aqueous solution (or in liquids of all but the lowest dielectric constant) the surface potential and charge of a particle is a reproducible quantity that gives valuable information both on the way the particle can interact with other particles or surfaces and on the nature of the particle surface. In the latter respect it is noteworthy that only a few particles and therefore a minute surface area, are necessary for the measurement.
So far as inter-particle behaviour is concerned the electric charge is one of the most important factors leading to stability of a dispersion against flocculation, coagulation or adhesion to surfaces. In all technologies involving dispersions or suspensions, whether these are required to be flocculated or de-flocculated, a knowledge of the particle charge and/or potential is a necessary pre-requisite to prediction of the behaviour of the system, either alone or in the presence of additives.
Increasing use is being made of measurements of the electrophoretic mobility of the various particles present in blood to help predict and prevent clotting of the blood and its adhesion to the walls of both natural and artificial blood vessels.
Quite apart from using electrophoretic mobilities to explain or predict the behaviour of particles or surface coatings, such measurements can be used as an aid to identifying the chemical groupings present at the particle surface. For example, the variation of particle surface charge with variations of pH of aqueous solutions gives important information on the dissociation of surface acidic and basic groups and can be used to identify them. Alternatively, in complex biological systems, the mobilities of the various particles present (which to some extent can be obtained without separation) can be used to identify these particles and may be characteristic of pathological conditions. In this connection it should be remembered that electrophoretic mobilities are most susceptible to change in conditions and therefore most characteristic of the particles, when the mobilities are small. Conditions such as pH can often be adjusted to achieve this.
Capabilities of the Rank Brothers Mk II Electrophoresis Apparatus
This Electrophoresis Apparatus can be used whenever the particles can be made visible relative to the suspending medium. Such visibility depends (apart from the intensity of the illumination and efficiency of the viewing optics) on the size of the particles and on the ratio of the particle refractive index to that of the surrounding medium. Using the quartz-iodine illumination unit of the standard instrument, aqueous dispersion of polystyrene particles (which have a rather unfavourable refractive ratio, about 1.1), shown to be visible down to a diameter of about 0.2µm. Particles with a more favourable refractive index ratio, e.g. carbon particles, can be seen down to much smaller sizes but it is difficult to give any precise limit in cases where monodisperse suspensions cannot be separated.
Lower Limit of Particle Size
One effective means of lowering the limit of particle visibility is use of a laser illuminator. Even a 3mW He:Ne continuous laser can concentrate more illumination into the observed volume than the 100 watt conventional illuminator and polystyrene particles of diameter only 0.09µm become visible. It must be remembered however that the necessary illumination power goes up very sharply as the size of the particle decreases below the figures quoted. Rank Brothers are pleased to perform free trials of particle visibility on samples sent to us by prospective purchasers of the apparatus.
The cylindrical cell, with extremely thin walls and ultra microscope illumination, is especially suitable when very small particles are involved.
Upper Limit of Particle Size
There is obviously no upper limit of particle size so far as visibility is concerned, the effective limit being set by the rate of gravitational fall or rise in the dispersion medium concerned. The flat cell is especially useful here because sedimenting particles fall neither out of view nor out of the stationary level. Moreover provided the rectangular cross section of the flat cell has its major dimension vertical, the sediment collects on an electro-osmotically unimportant surface so that measurements at the stationary level remain valid. The vertical gravitational component of the particles' motion can quite properly be ignored while the horizontal electrophoretic component is measured. Since the field of view is about 500µm across it follows that if times of vertical transit in excess of 20 seconds are accepted, the upper useful limit of particle diameter in aqueous solution at 25°C with particle specific gravity 2.0, is about 20µm. Particles with density nearer to that of water can be used up to much larger sizes.
Picture of Micro-Electrophoresis Apparatus setup for use with flat cell, especially suitable for:
- Large particles (which remain in field of view and stationary layer while sedimenting).
- Low conductivity solvents (silica walls of high resistivity).
- Applications requiring bright field or phase contrast illumination.
The Standard Mk II Micro-Electrophoresis apparatus comes with the following:
- Thermostatted water bath suitable for using cylindrical cell.
- Thermostatted water bath suitable for using flat cell.
- 100 watt Quartz iodide lamp illumination.
- Constant voltage and constant current electrode supply (0-100V, 0-5mA approx.).
- Circulating pump for water baths.
- Temperature controller for water baths (ambient to 50°C).
- A flat cell and holder.
- A cylindrical cell and holder.
- A pair of platinum electrodes.
- A handset incorporating a digital voltmeter, ammeter (to monitor Electrode voltage and current) and stopwatch.
- Binocular Microscope.
- 3mW laser can be supplied complete with mounting brackets to enable smaller particles to be measured.
- Rotating prism system enabling direct readout of particle speed (not automatically).
- Closed circuit monochrome television system, used instead of the binocular microscope to aid operator (not available to USA).
- Power Requirements:
- 110V, 220V or 240V 50/60Hz approx. 400VA (Voltage factory set).
- 80cm (w) x 30cm (d) x 54cm (h) approx.
- 40kg approx.
The manuals on this website are provided as PDF files, please see the Downloads page for links to reader software.
|ELE001A||Electrophoresis Apparatus Mark II 240V|
|ELE001B||Electrophoresis Apparatus Mark II 220V|
|ELE001C||Electrophoresis Apparatus Mark II 110V|
|ELE001D||Electrophoresis Apparatus Mark II 100V|
|ELE001D||Electrophoresis Apparatus Mark II 100V|
|ELE002A||Electrophoresis App. MKII rectangular cell only 110V|
|ELE002Y||Electrophoresis App. MKII rectangular cell only 240V|
|ELE002Z||Electrophoresis App. MKII rectangular cell only 220V|
|ELE003A||Rotating Prism System|
|ELE004A||C/Circuit TV Camera & Mount for MKII|
|ELE005A||TV - 9" Monochrome Monitor for MKII|
|ELE006A||3mW Laser and Mounts for MKII|
|ELE007A||Side illuminated graticule and eyepiece|
|ELE100A||Standard cylindrical cell for MKII|
|ELE101A||Standard 10 x 1 rectangular cell for MKII|
|ELE102A||10mm x 2mm rectangular cell for MKII|
|ELE125A||Pair of platinum electrodes|
|ELE126A||Pair of palladium electrodes|
|ELE133A||Stage Micrometer - Mount only|
|ELE134A||1mm x 10 Stage micrometer and mount|
|ELE161A||Front window for perspex water bath|
|ELE162A||Rear Window for perspex water bath|
|ELE163A||Rectangular cell holder|
|ELE164A||Cylindrical cell holder complete|
|ELE301A||Quartz Iodine bulb for MKII lamp|
Rank Brothers Ltd reserves the right to change specifications in the light of continuing development.