Process and apparatus for the quantitative determination of cations or anions by ion chromatography

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention consists of a procedure and an apparatus as follows: storage for the buffers, a sample inject valve, a chromatography column filled with ion exchange resin, a second ion exchange device to suppress the background ions, and a conductivity cell.
The second ion exchange device for suppressing background ions consists of a channel for the eluate which is at least partially partitioned by ion exchange membranes on the outside of which are electrolyte solutions and the adjacent spaces contain electrodes which can set up an electric field across the eluate channel.
Before going into the background of the various chemical methods to analyse anions and cations, we should look more closely at the cell (see diagram) to obtain a better understanding of the nature of the invention.
The cell consists of two ion exchange membranes (10,12) which are fixed between two platinum electrodes (14,16) attached to the side walls of the cell (not shown in diagram).
The eluate from the separation column flows through the channel marked 18 on the diagram.
The platinum electrodes (14,16) are connected to a potential which can be set to between 50 and 550 Volts which leads to currents of between 10 mA and 1.
2 A.
In the main a current of 120 mA is obtained running at 200 Volts.
The distance between the electrodes (14,16) and the adjacent ion exchange membranes (10 or 12) is between ca.
4 mm and ca.
50 mm, often more than not 8 mm.
The two membranes are usually between ca.
0.
1 mm and ca.
3 mm apart.
The two ion exchange membranes and the electrodes are pressure stable up to 30 bar (at the moment), so that they form in cross section three square channels, i.
e.
on either side of the eluate channel (18) there are side channels formed by the membrane and the anode electrode (14)--channel 20--and channel 22 between the cathode (16) and membrane (12).
The two side channels have electrolytic solutions pumped through them which act as electrode buffers.
Both these buffers have to be pumped from different buffer reservoirs in quite separate circulation channels through the side channels