Product category:
Titration equipment
News Release from: Stirling Service and Diagnostics | Subject: Thermometric titrimetry
Edited by the Laboratorytalk Editorial
Team on 11 September 2003
Titrate in a totally non-aqueous
environment
Solving the determination of weakly acidic species in non-aqueous media using thermometric rather than potentiometric titrimetry
Potentiometric titrations in the absence of water can be a real pain Everything is stacked against you
This article was originally published on Laboratorytalk on 19 Aug 2002 at 8.00am (UK)
Related stories
Analysis of moisture in oily, greasy matrices
The incompatibility of the highly polar Karl Fischer reagent with non-polar samples can introduce difficulties in the determination of moisture by this traditional approach
Free fatty acids analysis breakthough
A novel, easy to use thermometric titration method permits rapid, accurate, automated analysis of the free fatty acid (FFA) content of edible fats and oils with unprecedented precision and accuracy
Potentiometric titrations need a conducting medium to work, and most non-aqueous solvents are pretty lousy in this regard.
Further, the surface membranes of glass pH electrodes need to be properly hydrated to do their job.
This is hard when the titrating medium may be a polar solvent that is doing its best to dry out the glass membrane.
In some instances you can add a bit of water so that you can at least see some sort of endpoint, but it's by no means a universal approach.
Thermometric titrimetry is not bound by these restrictions.
You can titrate in a totally non-aqueous environment, since only the rate of change of temperature is of interest in locating the endpoint.
In some instances, there are distinct advantages in excluding water from the system.
Multitrator has designed a technique where small amounts of weakly acidic species can be determined in non-aqueous samples using a catalytic endpoint approach.
Vaughan and Swithenbank (1965) found that when dry acetone was used as a solvent, any acidic material could be titrated with base (eg KOH in dry methanol or isopropanol).
On the titration plot the red curve shows the actual temperature of the solution gently rising until all acid in the sample is consumed.
The first excess of base acts catalytically on the acetone to form diacetone alcohol with the considerable evolution of heat.
An advantage of the procedure is that because the endpoint is defined by the onset of the reaction of base with the acetone solvent, and not by the heat of neutralisation of the weak acid with base, small amounts of acidic species may be determined.
A disadvantage is that it is unable to discriminate between various species (say on the basis of pK) and thus is primarily useful when a total acid value is required.
The procedure has been successfully evaluated for carboxylic acids (mono and diprotic), hydroxy acids, phenols (mono and polyhydric), phenolic acids, keto-enols, imides and aromatic nitro compounds.
• Stirling Service and Diagnostics: contact details and other news
• Email this article to a colleague
• Register for the free Laboratorytalk email newsletter
• Laboratorytalk Home Page
Search the Pro-Talk network of sites
