Product category:
Liquid Analysis: Titration, HPLC, IC
News Release from: Metrohm UK | Subject: Alkali analysis
Edited by the Processingtalk Editorial
Team on 20 June 2007
On-line.alkali analysis in the process
industry
Throughout virtually all industries, ranging from food to steel, from microprocessors to chemicals as well as car making, the alkali concentration during the production process is of vital importance
The alkalis used in all these industries may very well differ in shape and concentration, like a few percent of alkali in a potato peeling plant or an ammonia concentration in a wafer plant They do have one thing in common though, that is in all cases the concentration of the free Hydroxyl ion and/or the total of free and bonded of the same play a decisive role in the process to produce a product with an acceptable quality
This article was originally published on Processingtalk on 2 Jul 2008 at 8.00am (UK)
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It is very appealing to think that from measuring the pH value one could derive the alkali concentration.
For several reasons however this is not the case.
The mV value generated by free hydroxyl ions at the glass electrode (later in the measurement device converted to pH) is often suppressed by other ions.
Or the alkali is not fully dissociated so the pH value only is expressing part of the alkali.
Even in those rare cases all conditions are right, still the accuracy achieved will be poor.
This is explained by the fact that the glass electrode works according to Nernst's law, meaning the logarithm of the concentration creates a linear (mV) signal.
Reversibly, obtaining concentration from the pH value, the signal has to be "de-logged", generating a big error.
The only method available to get the accuracy right is titration.
Because here the mV or pH value at the electrode is only a means to detect the equivalence potential, and from that the ml value of the consumed titrant (acid) coming from a burette.
This ml value is linear to the concentration of alkali.
Due to the steep shift in mV (pH) around the equivalence point the accuracy of the value is less significant .
With the availability of refined titration methods, done by the microprocessor, titrant volumes can be determined with an inaccuracy smaller than 0.05%.
Recommended Analyzers:.
For single steam and single chemistry applications: 2016 Titrolyzer.
For multiple streams and multiple chemistries: 2040 Process Analyzer.
For further information please contact Metrohm UK. Request a free brochure from Metrohm UK ...
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