Product category:
Titration equipment
News Release from: Metrohm UK | Subject: Applikon 2011 and ADI 2040
Edited by the Laboratorytalk Editorial
Team on 02 August 2006
On-line acid analysis made easy
In many industries, from food to steel, from microprocessors to chemicals as well as car making, the concentration of acid during the various stages of the production process is of vital importance
The acids used in all these industries may very well differ in shape and concentration, like a few percent of acetic acid (vinegar) in mayonnaise or a high concentration of hydrofluoric acid in an etching operation They do have one thing in common though, that is in all cases the concentration of the free hydrogen 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 Laboratorytalk 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 acid concentration.
For several reasons however this is not the case.
The mV value generated by free hydrogen ions at the glass electrode (later in the measurement device converted to pH) is often suppressed by other ions.
Or the acid is not fully dissociated so the pH value only is expressing part of the acid.
Even in those rare cases when 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 coming from a burette (or precision pump).
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 analysers: For single steam and single chemistry applications: Applikon 2011 Titrolyzer For multiple streams and multiple chemistries: Applikon ADI 2040 Process Analyzer. Request a free brochure from Metrohm UK ...
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