Titration technique is widely used in various
analytical service providing and teaching laboratories. In this technique, a
solution of known concentration is used to determine the concentration of an
unknown sample. The currently used titration methods consume large volume
of reagents and samples (hundreds of milliliter) and glassware like
burette and pipettes.
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| Design of iodometric paper test card (source) |
Titrations now can be carried out in a piece of paper
modified with appropriate reagents. Professor Lieberman's group from University
of Notre Dame recently has described an
iodometric titration method in a paper card-published in Analytical
Chemistry journal. Titration in the paper test card starts by
applying a test solution to the test card in which multiple dried reagents have
been stored separately. The reagents reconstitute and combine through a
surface-tension enabled mixing (STEM) after the application of unknown
solution. The end point of the titration is indicated by the appearance of blue
complex of iodide and starch. The signal can also quantitated by using image-processing
software.
Iodometric titration involves a redox reaction used
to determine the amount of variety of analytes of interests. The authors used
this method to quantitate the iodine present in common salt and also
demonstrated the versatility of the titration device by quantifying beta-lactam
antibiotics via an iodometric back-titration. In later example, the antibiotic
was degraded in base to obtain a redox active thiol. The reaction mixture was
then acidified and a known amount of excess triiodide is added to oxidize the
thiol. Ureacted triiodide is back-titrated with thiosulfate.
Unique feature of the iodometric test card is its
ability to store multiple reagents separately for long time and allowing them
to mix and react when desired.
The paper titration technique would be very useful in
developing countries and in remote locations-especially. It is cheap, easy to
perform and requires small amount of reagents. Also, generates less waste.
Authors described the stability of this test card (stored reagents) for ~20
days at temperature 40deg C. It is not clear if the results obtained at above
conditions will be valid for more than 20 days and higher temperature combined
with humidity. Lets consider a village in India. Some of the Indian villages
see temperatures more than 40 deg C (easily 45) that combined with high
percentage of humidity. Will the test card work in this location? Proper
packaging can protect effect of humidity, however. If the test card is not
manufactured at local level, then 20 days time frame is not enough. It will
take months for the cards to be used in field.
This method has great scope to be introduced in to
the classroom-teaching labs.
Will this new method replace traditional ways of
doing iodometric titrations?
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