DE2808229A1 - Electrophoresis cell to measure zeta potential - having two transition pieces with hemispherical couplings and electrodes in contact with the liquid holding electrophoresis cell between the - Google Patents

Abstract

Electrophoretic system is for measuring the zeta potential in order to determine the electrophoretic velocity. The system uses a transparent measurement cell whose temp. is held constant. A microscope is used to monitor particle movement. An electrical source generates an electric field The electrodes are mounted in the inlet and outlet branches and are in direct contact with the liquid. The electrode vessels serve as connection pieces and each has push in connections. For measuring the zeta potential of liquids such as electrophoretic lacquers, emulsions, industrial effluents, pharmaceutical suspensions, medicinal cell research esp. cancer diagnosis. The problem with existing systems is their complicated construction and the difficulty of removing air.

Description

ELECTROPHORESIS SYSTEM

To understand the electrokinetic processes in suspensions, e.g. of phosphors in aqueous solutions such as those in color picture tube technology are used, the ((zeta) - potential of the suspended particles is a decisive one Size.

The r-potential gives direct information about the electrical Double layer and enables the behavior of colloidal systems to be described in where coagulation, flocculation, filtration and flotation play a role. Consequently there are a variety of applications for the measurement method of the r-potential such as electrophoretic paintwork, emulsions, industrial wastewater treatment, pharmaceutical suspensions, medical cell research, in particular cancer diagnosis.

There are several devices on the market for measuring the zeta potential, for example the "cytopherometer" from Zeiss.

A major disadvantage of the device is its complicated structure of the electrode vessels in the electrophoresis system of the device. In Fig. 1 there is one disadvantageous structure outlined. 1 means the measuring chamber with which the actual one Measurement takes place and 2 an electrode vessel with the electrode 3. Through cell membranes 4, the suspension 5 to be measured is chemically separated from the electrodes. The electrodes dive in a physiological saline solution 6. Before performing a For the measurement, the area between the electrode and the measuring chamber must be free of air bubbles; this process is very tedious and often unsuccessful. It predominantly accumulates Air bubbles in the tubes 7 or below the cell membrane 4.

The object of the invention is to provide a simplified electrode system, that overcomes the disadvantages. In Fig. 2 the improved device is shown. 8 shows the electrode vessels. Intermediate pieces 9 are used to compensate for mechanical Tension and protect the measuring chamber from breakage.

The measuring chamber is to be provided with two standard ground joints. The intermediate pieces accordingly have two standard ground joints on the chamber side and two spherical ground joints on the electrode side 10 onto which the electrode vessels fit.

Because the electrodes are directly connected to the solution to be measured electrolytic processes can disturb the electrical field in the leads occur, whereby within the measuring cell 1 another electrical Field appears as that applied to the feeding electrodes 3. That would be a wrong one Determination of the zeta potential result. Therefore, according to the present invention, there are two Measuring electrodes 11 built into the spacers, so that the voltage required for the Determination of the zeta potential is decisive, is determined correctly.

The feed electrodes 3 are connected to a voltage constant that allows polarity reversal. If Um denotes the voltage between the measuring electrodes and L denotes their distance, then the zeta potential of colloidal particles in a suspension, measured in a device according to the concept of the invention, is determined according to the formula: In this, n and e denote the viscosity or dielectric constant of the solution under investigation and v the electrophoretic velocity of the particles, as measured with the aid of a microscope and the measuring chamber.

During experiments on different electrophoretic systems it was without exception found that undesirable currents occur within the measuring cell, which significantly falsify the measurement result.

In the undisturbed case, the direction of movement of the particles would be in the stationary plane of the measuring cell from the sign of the zeta potential and the Depend on the direction of the applied field.

In the practical case - as has been determined - the superimposed Particle movement is a flow of the solvent that leads to the Reversing the polarity on the electrodes (field reversal), the particles are not the same Have speed in the opposite direction. With strong currents there may be no direction reversal.

The reasons for undesirable currents can be, for example: a) No exact adjustment of the measuring microscope to the stationary plane of the measuring cell; b) Electrochemical processes within the measuring system <gas formation); c) imperfect Pressure equalization in the measuring system; d) Convection due to temperature gradients Joule heat; e) Soiling on the cell walls and thereby disturbance of the electroosmosis.

The above-mentioned disturbances lead to incorrect measurement results.

Such errors in the measurement result were found in series examinations the described measuring system switched off in the following way: During a measurement the voltage is reversed several times. This means that different values occur in the measuring cell Velocities vm + and vm of the colloidal parts, both in magnitude and in the direction. By determining the different transit times of the particles lets eliminate the unwanted flow.

Determination of the electrophoretic mobility of the suspended Particle takes place with the help of the following consideration.

With respect to a positive directional axis pointing to the right, s are the following speeds must be taken into account: vs: speed of the flow v +:: Velocity of a particle when the positive pole is on the left as a result of the zeta potential v ~: like v +, but after reversing stm + | measured speed of a particle with positive polarity Vm-: corresponding with polarity reversal The relationship between the speeds is described by equations (a) to (c).

- = - v (a) Vm + = v + + vs (b) vm- = v ~ + vs (c) To the system of equations (a) - (c) to solve for the running time t +, which only depends on # and the field direction, several possible cases are to be investigated.

After reversing the polarity, the particles can run in opposite directions (Flow less than electrophoretic speed, i.e. t5> t +) as well have the same direction of travel (t5 <t +).

A measuring speed can be zero or the movements are opposite same. The consideration of these cases resulted in Table 1 with the associated Determination equations (1) to (6) are derived.

Equations for determining the transit times t + and the flow time ts: The reproducibility of the measured values was checked on many systems; the deviations were in the range of the measurement error.

The possibility of subjective measurement errors is microelectrophoretic with this one Proceedings cannot be ruled out.

The linear error analysis shows that the following relationship applies to the error in the 5-potential: Experience shows that this error is approx. 5%.

Another idea of the invention is the cooling chamber for to design the measuring cell from two parts into which the measuring cell is glued. The advantage of the proposed chamber is that the measuring cell can be directly observed is accessible and the cooling liquid is not between the measuring cell and the microscope objective occurs so that no disruptive optical effects occur.

Fig. 3 shows the structure of the two-part cooling chamber. A groove 12 is used for inserting the chamber into a carrier plate that is not listed. The cooling tubes are connected to the supports 13. Tabs 14 and notches 15 are used for Hold the measuring cuvette, and there is also the conical cutout 16 for the microscope objective drawn in, which leaves a circle of vision of 10 mm in diameter open.

The measuring cell fastened in the chamber is protected against breakage and can be removed for cleaning together with the cooling device.

The exchange of the cell is therefore very convenient and quick, which is particularly advantageous for series examinations. Case plus pole left: criterion sign equations No. Direction of movement in the microscope Opposite running direction after reversing the polarity ts> t + 1 -> tm + <tm <0 (1), (4) 2 <- tm +> tm ~> 0 (2), (4) 3 -> tm +> tm ~ <0 (2), (4) 4 <- tm + <tm-> 0 (1), (4) Same running direction after reversing polarity ts <t + 5 -> tm + <tm- <0 (3), (5) 6 -> tm +>tm-> 0 (3), (6) 7 <- tm +> tm- <0 (3), (6) 8 <- tm + <tm-> 0 (3), (5) A measuring speed is zero 9 'vm- = 0> O t + = 2tm + 10 -> vm- = 0 <0 t + = 2tm + 11 -> vm + = 0> 0 t + = 2tm- 12 <- vm + = 0 <O t + = 2tm- No current, opposite movements are the same 13 <tm + = tm-> O t + = tm + 14> tm + = tm- <O t + = tm + The same directions of movement and the same measuring times 15 <- tm + = tm- = ts # = 0 16 -> tm + = tm- = ts # = 0 Table 1 blank page

Claims (4)

Electrophoresis system Claims 1. Electrophoretic system for a zeta potential measuring device for measuring electrophoretic velocities, Consists of a transparent measuring cuvette, the temperature of which is kept constant can be, a measuring microscope for observing the movement of particles in the measuring cell and a supply device which generates an electric field in the measuring cell can, characterized in that the electrodes are placed in the inlet and outlet vessels and are in direct contact with the solution to be measured, whereby the electrode vessels each consist of a first vessel in which the electrodes are located, and one second vessel that serves as a connecting piece and is provided with two cuts. 2 electrophoresis system according to claim l, characterized in that Two measuring electrodes are enclosed in the spacers for measuring the electrical Field which sets the suspended particles in motion. 3. Electrophoresis system according to claim 1 and 2, characterized in that that a constant polarity reversible voltage is applied between the feed electrodes (5) is, but the field strength occurring in the measuring cell between the measuring electrodes (4) is established. 4. Electrophoresis system according to claim 1, characterized in that that the temperature chamber of the measuring cell consists of two separate, important chambers, the measuring cuvette and the front chamber being glued into the rear chamber contains a conical opening for better observation of the measuring cell and on the rear chamber and the measuring cell is glued on.