Sunday, January 25, 2015

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.

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