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The classical ion selective electrode (ISE) has an inner reference electrode of Ag/AgCl with a liquid inner electrolyte and an ion selective membrane, the challenge was to design a solid contact internal metal electrode and ion selective membrane with a stable potential.
Metrohm have developed an ISE based upon ceramic thick film with a gold electrode/polymer layer/membrane layer which has a steady potential.
The advantages of this electrode design are obvious. The first one is cost, the fig above shows the replacement sensor part therefore the whole electrode does not need replacing.
In addition more advantages are
- Fewer replacement components
- No contamination and ionic diffusion of inner electrolyte
- Increased reproducibility due to automated production steps
- Semi-disposable sensor section eliminates deterioration in determination results.
Water Hardness Application
The electrode has initially been dedicated to the one water hardness application. This has enabled Metrohm to tailor scion conditioning to one application. It was found the first titration also was a break in determination with the second determination results being used. The method was then validated because a limited number of measurements were verified during development.
The figure below shows a titration curve from the first determination, the figure afterwards shows the 1000th determination. The curves are very similar showing no degradation in the scIONs performance, therefore Metrohm suggest replacing the sensor part after 1000 titrations thus minimising any effect on results.
First Titration
1000th Titration
Practical Issues from Water Hardness Titration
The TISAB needs to be fresh, the acetylacetonate solution used as the TISAB ages quickly which was important for Ca/Mg resolution in the titrationcurves. I is recommended this is changed weekly. The scION life specifications of 1000 titrations is for drinking water only, other samples may have a shorter life cycle of the probe, a suitable indicator of the life span of the scION will be titration jump height in mV, if this begins decreasing over time it is an indicator of an aging effect of the probe. Do not leave in sample solution after titration an no wet storage is necessary.
Product Information
- scION for quick exchange in sachet Ca2+ 6.0509.000
- Permanent Shaft/Holder/Adapter with Connector G 6.1241.070
For more information and a quotation, please contact us on 01928 579 600 or email us
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