Direct sensing of total alkalinity profile in a stratified lake

Abstract

doi: 10.7185/geochemlet.1709We demonstrate the direct detection of a total alkalinity depth profile through the use of an integrated thin layer electrochemical modulation instrument which acts as an alkalinity sensor. The technique uses a chemically selective proton pump that alters the concentration of hydrogen ions in the thin layer sample. As the proton pump releases hydrogen ions the resulting pH is recorded at the pH probe placed directly opposite the thin sample gap. This results in an acid-base titration that takes place directly in the thin layer sample and therefore obviates the need for traditional sample manipulation. Collected samples from a stratified lake were assessed with this alkalinity probe to record a total alkalinity profile, indicating a substantial increase from 2.59 to 4.11 mM with depth. Results of the new method were in excellent agreement with titration alkalinity data, and offer the potential for autonomous on site measurements of this key parameter.

Electrochemical Analysis for Total Alkalinity of Water by the Measurement of Cathodic Prepeak of Quinone Caused by Surplus Acid

“…7) In addition to the neutralization titration method, spectrophotometric and electrochemical analyses have been reported to determine the total alkalinity of water samples. [8][9][10][11][12][13] Spectrophotometric analysis determines the total alkalinity of a water sample as follows: the excess hydrogen ion concentration obtained after a neutralization reaction with a standardized acid is spectrophotometrically determined using the color changing of a bromocresol green indicator based on a different pH, and then the alkalinity of the water sample is calculated from the excess hydrogen ion concentration. [8][9][10] On the other hand, electrochemical analysis determines the total alkalinity of a water sample as follows: inorganic bases in the test solution are neutralized by hydrogen ions released from a selective polymeric membrane (proton pump), and then the resulting pH in the test solution is potentiometrically assessed using a pH electrode.…”

“…[8][9][10] On the other hand, electrochemical analysis determines the total alkalinity of a water sample as follows: inorganic bases in the test solution are neutralized by hydrogen ions released from a selective polymeric membrane (proton pump), and then the resulting pH in the test solution is potentiometrically assessed using a pH electrode. [11][12][13] Thus, both methods measure hydrogen ion concentration to determine total alkalinity, and not a total equivalent concentration of inorganic bases determined by the neutralization titration such as the official method of the Japanese Industrial Standards (JIS). 7) To the best of our knowledge, an electrochemical analysis such as voltammetry using a bare carbon electrode has not been successfully provided for determining a total equivalent concentration of inorganic bases.…”

Modification of Proton Pump Membrane using Polyvinylpyrrolidone (Pvp) for Potential Total Alkalinity Sensing

“…However, this method is time-consuming and can only be applied for a single measurement at one time for a sample. Recently, Afshar in 2017 developed a new approach using polymeric functional membrane [11], as the utilization of polymers has been of interest and there are high demands for more advanced functional materials. In this approach, the proton pump membrane was synthesized using porous polypropylene (PP) membrane as a supporting material [11].…”

Impacts of irrigation water quality, associated soils characteristics and on-farm practices on paddy yields

“…Total alkalinity is a measure of water's capability to neutralize added acids (Hauser, 2018). It establishes the buffering capacity of water (Afshar et al, 2017). The major chemicals that contribute to the alkalinity of water include dissolved carbonates, bicarbonates and hydroxides (Nand & Ellwood, 2018).…”