Analysis of moisture in oily, greasy matrices
A
Stirling Service and Diagnostics product story
Edited by the Laboratorytalk editorial team
Aug 19, 2002
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
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.
In a recent article in 'Lab Asia' it was noted that "crude oil samples are hardly soluble in the Karl Fischer reagent as they mainly consist of long-chain hydrocarbons.
Moreover, the low conductivity of the oils can interfere with the electrochemical indication in direct titrations".
It was also mentioned that such samples foul the Karl Fischer cell, and that reducing agents present may oxidise iodine in the Karl Fischer reagent, leading to artificially high values for moisture content.
The chemistry employed by Multitrator does not suffer from these problems.
2,2 dimethoxypropane (DMP) reacts endothermically with water to produce sharp, reproducible endpoints when catalysed by a small amount of an acid such as methyl sulphonic acid.
DMP is soluble in non-polar solvents such as alkanes, cyclohexane, and even mineral turpentine.
These solvents may be used to dissolve the sample, and a small amount of dry isopropanol is added to ensure the dissolution of the water component.
There are no precipitates to foul the sensor, a thermistor that functions regardless of the solution being polar or non-polar.
Further, titrations are conducted in cheap polypropylene beakers, which are easily cleaned.
The complex and expensive distillation accessory proposed in the article is unnecessary.
DMP reagent is indefinitely stable, does not react with water unless acid catalysed, and is unaffected by oxidising or reducing reagents.
As well as being applied to the moisture content of oils, the thermometric DMP titration can be applied to samples such as margarine, butter, cosmetic creams pastes, emulsions and slurries.
Further details may be obtained from the Multitrator website (link above).
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