Iodometric titration on paper device #PADs

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?

Acid-base titration on paper microfluidic device: will it replace traditional acid-base titration?

u-PAD for acid-base titration (source)

Research in paper-based microfluidic analytical devices (u-PADs) has evolved very fast in past couple of years. Recently, scientists from Okayama University, Japan have reported a technique to carry out acid-base titrations in PADs and the work has been published in journal Analytical Chemistry. 

The wax printed u-PADs consisted of ten reaction (acid-base reaction) and 10 detection reservoirs. The detection reservoirs were applied with a constant amount of phenolphthalein (indicator) and the reaction reservoirs were applied with various amount of a primary standard potassium hydrogen phthalate (KHPth). Only less than a microliter volume of the solutions were needed. The base (e.g., NaOH) was dropped onto the center reservoir of the device. As the base wicked towards the reaction reservoir, it then reacted with the acid and if any extra NaOH remained it then moved further and reached to the detection reservoir to produce a pink color. The number of detection reservoirs with no color change was used to determine the concentration of NaOH. The authors have tested this technique using other acids like nitric acid, hydrochloric acid, sulfuric acid, and acetic acid.

Acid-base titration is widely used in teaching chemistry  and in variety of analytical services. The currently used titration methods involve large volume of reagents and samples; glassware (burette and pipettes).

The new u-PAD being used in field testing (source)

The new method takes only about a minute to complete the titration and is more advantageous than classical titration methods in terms of speed, portability, and disposability.

Eventhough the micro-titration device was shown to be stable for couple of days, it requires further improvements to make the device stable for longer time. The reagents stored in the PADs degrade with time. Therefore the reagents have to be applied at the time of use only. Also, temperature plays bad role for the stability of the PADs. Therefore not suitable for places with higher ambient temperature (e.g., summer time in India).

As PADs are cheap, this new titration technique may replace the traditional titrations, specially in developing countries. Teaching settings can immediately adopt the technique.