Distance-based paper microfluidics as environmentally friendly platforms for monitoring acid-base titrations

Abstract

The goal of green chemistry is to reduce the impact of chemical processes on the environment. In this context, it is important to develop new analytical tools that comply with the principles of green analytical chemistry (GAC) to contribute to the sustainable development of the planet. This study describes the development of an environmentally friendly methodology using paper-based analytical devices (µPADs) to perform acid-base titrations by distance-based measurements. The devices were composed of a circular zone defined with 5 mm diameter connected to a rectangular channel of 40 mm long × 3 mm wide. The titrations of acidic (strong and weak) and alkaline (strong and weak) solutions were successfully demonstrated using 10 µL of titrant solution and 10 µL of sample solution. The solution added into the zone travels different distances depending on the concentration of the titrated, thus promoting the channel coloration or discoloration. The distance measurements covered by the titrated solutions were obtained recorded with a digital caliper. As proof-of-concept for quantitative purposes, the µPAD was then used to determine the acetic acid content in commercial vinegar. The average distances ranged from to 32.0 to 32.5 mm and the concentration values ranged from 4.3 to 4.6% (m/v). Conventional acid-base volumetry was used as a control method, and the obtained results demonstrated no statistical difference at 95% confidence level. Lastly, the 12 principles of GAC were analyzed to evaluate the suitability of the proposed method. Considering a unified scale between 0 and 1, the final green value was 0.72. Titrations with distance-based detection on µPADs were found to be a technique with fast responses and low cost that can be used as a replacement for conventional practices in teaching laboratories or adapted for the detection of different analytes.