dc.description.abstract | Herein, we report on a reagentless electroanalytical
methodology for automatized acid−base titrations of water samples
that are confined into very thin spatial domains. The concept is
based on the recent discovery from our group (Wiorek, A. et al.
Anal. Chem. 2019, 91, 14951−14959), in which polyaniline
(PANI) films were found to be an excellent material to release a
massive charge of protons in a short time, achieving hence the
efficient (and controlled) acidification of a sample. We now
demonstrate and validate the analytical usefulness of this approach
with samples collected from the Baltic Sea: the titration protocol
indeed acts as an alkalinity sensor via the calculation of the proton
charge needed to reach pH 4.0 in the sample, as per the formal
definition of the alkalinity parameter. In essence, the alkalinity
sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration
in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement
with the values obtained by manual (classical) acid−base titrations (discrepancies <10%). Some crucial advantages of the new
methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2
week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the
sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a
discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future
digitalization of in situ acid−base titrations to obtain high-resolution data on alkalinity in water resources. | es |