Direct alkalinity detection with ion-selective chronopotentiometry

M G Afshar; G A Crespo; X Xie; Eric Bakker

doi:10.1021/ac500968c

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Direct alkalinity detection with ion-selective chronopotentiometry

Journal article

Peer reviewed

Direct alkalinity detection with ion-selective chronopotentiometry

M G Afshar, G A Crespo, X Xie and Eric Bakker

Analytical Chemistry, Vol.86(13), pp.6461-6470

2014

DOI: https://doi.org/10.1021/ac500968c

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Abstract

Analytical Chemistry

Chemical Engineering

Other Chemical Sciences

hydrogen

ions

liquid membranes

polypropylenes

chronopotentiograms

chronopotentiometry

concentration profiles

concentration ranges

diffusion layers

hydrogen phosphates

solution chemistry

trishydroxymethylaminomethane

We explore the possibility to directly measure pH and alkalinity in the sample with the same sensor by imposing an outward flux of hydrogen ions from an ion-selective membrane to the sample solution by an applied current. The membrane consists of a polypropylene-supported liquid membrane doped with a hydrogen ionophore (chromoionophore I), ion exchanger (KTFBP), and lipophilic electrolyte (ETH 500). While the sample pH is measured at zero current, alkalinity is assessed by chronopotentiometry at anodic current. Hydrogen ions expelled from the membrane undergo acid-base solution chemistry and protonate available base in the diffusion layer. With time, base species start to be depleted owing to the constant imposed hydrogen ion flux from the membrane, and a local pH change occurs at a transition time. This pH change (potential readout) is correlated to the concentration of the base in solution. As in traditional chronopotentiometry, the observed square root of transition time (Ï„) was found to be linear in the concentration range of 0.1 mM to 1 mM, using the bases tris(hydroxymethyl)aminomethane, ammonia, carbonate, hydroxide, hydrogen phosphate, and borate. Numerical simulations were used to predict the concentration profiles and the chronopotentiograms, allowing the discussion of possible limitations of the proposed method and its comparison with volumetric titrations of alkalinity. Finally, the P-alkalinity level is measured in a river sample to demonstrate the analytical usefulness of the proposed method. As a result of these preliminary results, we believe that this approach may become useful for the in situ determination of P-alkalinity in a range of matrixes.

Details

Title: Direct alkalinity detection with ion-selective chronopotentiometry
Authors: M G Afshar (Author) - University of Geneva, Switzerland
G A Crespo (Author) - University of Geneva, Switzerland
X Xie (Author) - University of Geneva, Switzerland
Eric Bakker (Author) - University of Geneva, Switzerland
Publication details: Analytical Chemistry, Vol.86(13), pp.6461-6470
Publisher: American Chemical Society
Date published: 2014
DOI: 10.1021/ac500968c
ISSN: 0003-2700
Organisation Unit: University of the Sunshine Coast, Queensland
Language: English
Record Identifier: 99449077402621
Output Type: Journal article

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