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.
|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?