Rank Brothers Ltd

Charge Analyser II

Features

Charge Analyser II


General

The Rank Brothers Charge Analyser II is a completely automatic polyelectrolytic titrator. Polyelectrolytic titration enables determination of ionic charges of polymers in solution and surface charges of colloids. The system is microprocessor controlled giving the operator a user friendly interface that has been designed to ensure novice operators can quickly and easily carry out accurate titrations. The cell has been designed to measure the charge of liquid samples or liquid samples containing only small particles, thus paper stock for example, will need to be filtered to remove particles above 1µm before a titration.

Applications

Waste water treatment
  • Optimising dosage of flocculents.
Paper manufacture
  • Determination of charge density of unknown polymer (e.g. fixative, wet strength agent or retention aid).
  • Determination of the concentration of a known ionic polymer in solution.
  • Determination of the concentration of anionic polymers (interfering substances in the water circuit).
  • Determination of the charge demand of paper stock or wire water by back titration.
Colloid science

Principle of Polyelectrolyte Titration

The principle of polyelectrolyte titration is based on the fact that the standard anionic and cationic polymers form 1:1 compounds with each other based on their charge and are thus directly equivalent to an acid/base neutralisation.

Principle of Polyelectrolytic Titration

The titrator uses a standard anionic and/or a standard cationic polymer to determine the equivalent charge of the sample. Potassium Polyvinyl Sulphate (PVSK) is used as the standard anionic polymer and Hexamethrine Bromide (Polybrene) is used as the standard cationic polymer. The titration end point is determined using a streaming current detector cell or a photometer cell.

The Rank Brothers Charge Analyser II (CAII) will perform a polyelectrolytic titration automatically and consists of three main parts: the detector cell, the control unit, and the precision metering unit. The three parts are described in more detail below.

The Detector Cell

Two types of cell are available for use with the CAII, the streaming current cell and the photometer cell. The cells can easily be changed by switching off the CAII and connecting whichever cell is required.

The cell is easily detached from the standard assembly to enable cleaning of both the cell and the piston after every titration. The titration is carried out in disposable plastic cups, the cup is placed on the stirrer unit (supplied with the metering unit) and the cell is partially immersed in the sample to enable a titration to be carried out.

The Streaming Current Detector Cell

The streaming current detector cell comprises of a stand (with incorporated drive motor) and the measuring cell. The cell consists of a cylinder closed at one end with a pair of electrode rings, one at the closed end and one in the middle of the cylinder. A piston oscillates axially inside the cylinder at a speed of approximately 250rpm streaming sample past the two electrodes. Polymers have a tendency to adsorb onto interfaces and thus become fixed to the piston and cylinder walls. The mobile counter-ions of the fixed electrolyte create an electric current due to the partial charge distribution between the two electrodes in the cylinder wall. Thus, the cell produces a sinusoidal voltage of about 4Hz.

The Control Unit

The control unit houses the interface electronics and power supply for the cell, plus a microprocessor card to control the complete system. The front panel consists of a 2 line by 24 character liquid crystal display (LCD), four keyboard switches, two LEDs, and a BNC socket. The top line of the LCD shows current values of the charge of the sample and the total volume of polymer dosed (when this information is available). N.B. The value of the charge is not calibrated to any specific units, but is proportional to the value of the signal from the cell. The sign of the charge is also displayed so that the user immediately knows whether the sample is anionic or cationic.

The second line of the display indicates the status of the unit, for example: Titrating or displays useful help information such as: Press <TITRATE> to start. The four keys are labelled <MOTOR>, <TITRATE>, <PRINT>, and <STOP>, with the first three keys having built-in LEDs to indicate their status. The two main LEDs are used to indicate when the metering unit is dosing and when the titration has finished. The BNC socket connects the unit to the cell and is on the front panel to enable easy connection during cell cleaning.

The rear panel has connections for the power inlet lead, the cell motor, a parallel Centrionics printer, and the metering unit. The printer socket allows connection to a printer with a Centrionics parallel interface and will print the charge value, the amount of polymer dosed, and the phase angle of the charge signal. This information is printed after every measurement cycle (10-30 times a minute depending on whether dosing occurs or not).

The microprocessor has complete control of the system, including the cell motor and the metering unit. Once the operator has determined the correct standard polymer (anionic or cationic) to use, the system is able to carry out a fully automatic titration. The control unit determines the volume of polymer to dose into the sample from the magnitude of the charge and then proceeds to titrate until the phase of the streaming current has inverted. The end point dose will then be calculated from the minimum charge value during the titration and will be displayed on the LCD.

The microprocessor is monitoring various functions; if problems occur it will display diagnostic information relating to the printer, the cell connections, etc. It also has an internal buzzer to warn the operator of faults, invalid key presses, and the titration end.

The Metering Unit

The supplied metering unit is a Metrohm 665 Dosimat complete with remote keypad, magnetic stirrer and stand, and two 10ml exchange units complete with 1 litre reagent bottles. The Dosimat is connected to the control unit enabling the control to dose exact volumes and to refill an exchange unit at the beginning and end of a titration. The Dosimat is a versatile programmable metering unit and can be used completely independently from the CAII for other laboratory applications.

The Carrying Cases

Carrying Case

The CAII is supplied complete with two custom designed carrying cases, enabling titrations to be carried out at particular sites in the field. One case contains the CAII itself, while the other holds the metering unit. The cases have lockable catches and aluminium lined outer skins for extra strength and would be suitable to take as luggage on an aircraft. The inside of the cases are foam lined with cut outs for individual parts of the system. The cases can also be used for storage of the system, ensuring that parts do not become damaged or lost.


Technical Data

General

Power Supply (control unit):
110-120V 25VA or 220-240V 30VA 50/60Hz selectable via rear panel switch.
Weight (CAII including case):
16kg approx.
Weight (metering unit including case):
18kg approx.
Size (CAII case):
450mm (h) x 430mm (w) x 250mm (d) approx.
Size (metering unit case):
610mm (h) x 350mm (w) x 300mm (d) approx.

Control Unit

Printer interface
25 way D connector for use with an IBM compatible printer lead. The interface is a Parallel Centrionics type suitable for the majority of printers with a parallel interface.

Metering Unit

The supplied metering unit is the Metrohm Dosimat 665 complete with two 10ml exchange units giving a 10ml maximum dose and an accuracy of 20µl.


Operating Manual

The manuals on this website are provided as PDF files, please see the Downloads page for links to reader software.

Charge Analyser II Manual (472KB)


Ordering Information

When ordering a Charge Analyser II, a choice of detector cells is available. Detector cells may also be bought separately at a later date.

Order Code Description
CHA004A Charge Analyzer with streaming cell and case excluding dosimat
CHA005A Charge Analyzer with photometer cell and case excluding dosimat
CHA006A Charge Analyzer with streaming cell and photometer cell excluding dosimat
CHA007A Charge Analyzer with streaming cell excluding dosimat and case
CHA008A Charge Analyzer with photometer cell excluding dosimat and case
CHA009A Charge Analyzer with streaming cell and photometer cell excluding dosimat and case
CHA100A Charge Analyzer streaming cell
CHA101A Charge Analyzer photometer cell complete with clamp

Rank Brothers Ltd reserves the right to change specifications in the light of continuing development.

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