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Micromachines 2017, 8(5), 139; doi:10.3390/mi8050139

Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone

1
Instituto de Química, Universidade Federal de Goiás, Campus Samambaia, Goiânia, GO 74690-900, Brazil
2
Instituto Nacional de Ciência e Tecnologia em Bioanalítica, Campinas, SP 13084-971, Brazil
*
Author to whom correspondence should be addressed.
Academic Editors: Frank A. Gomez, Carlos D. Garcia and Nam-Trung Nguyen
Received: 30 January 2017 / Revised: 19 April 2017 / Accepted: 28 April 2017 / Published: 2 May 2017
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Abstract

This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with acid–base titrations examples, where jaboticaba peel extract was used as a natural pH indicator. The color intensity was captured using a smartphone and analyzed through a free App named Photometrix®. Before titrations, color intensity versus pH was calibrated to be used as a reference in titrations as (i) strong acid versus strong base; (ii) strong base versus strong acid; and (iii) weak acid versus strong base. In all examples, images were obtained after the addition of each aliquot of titrant solutions. The obtained titration curves showed the same behavior as the conventional titration curves. After evaluating the feasibility of the proposed methodology, the concentration level of acetic acid was obtained in three vinegar samples. Although the obtained values ranged from 5% to 8% compared to the concentrations on the conventional method, the proposed methodology presented high analytical reliability. The calculated concentrations of acetic acid in three samples ranged from 3.87% to 3.93%, and the proposed methodology did not significantly differ from classic acid–base titration at a confidence level of 95%. The acid–base titration on paper-based devices is outstanding, since any titration can be completed within 5 min using 20 µL volumes. Besides, the use of a smartphone to capture images followed by analysis in a free app offers simplicity to all users. The proposed methodology arises as a new strand to be exploited in the diffusion of the analytical chemistry education field as well as an alternative for quantitative analysis with extremely simplified instrumentation. View Full-Text
Keywords: cell-phone analysis; chemical education; instrument-free chemical assays; microfluidic paper-based analytical devices; paper microfluidics; spot tests cell-phone analysis; chemical education; instrument-free chemical assays; microfluidic paper-based analytical devices; paper microfluidics; spot tests
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Nogueira, S.A.; Sousa, L.R.; Silva, N.K.L.; Rodrigues, P.H.F.; Coltro, W.K.T. Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone. Micromachines 2017, 8, 139.

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