TY - JOUR
T1 - No more conventional reference electrode: Transition time for determining chloride ion concentration
AU - Abbas, Yawar
AU - de Graaf, Derk Balthazar
AU - Olthuis, Wouter
AU - van den Berg, Albert
N1 - eemcs-eprint-24685
PY - 2014/4/22
Y1 - 2014/4/22
N2 - Ion selective electrodes (ISE) are used extensively for the potentiometric determination of ion concentrations in electrolytes. However, the inherent drift in these measurements and the requirement of a stable reference electrode restrict the feasibility of this method for long-term in-situ applications. This work presents a chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode for measuring chloride ion concentration. An anodic current pulse is applied to a Ag/AgCl working electrode which initiates a faradaic reaction that depletes the chloride ions near the electrode surface. The rate of change in potential at the Ag/AgCl electrode, due to chloride ion depletion, reaches an inflection point once the chloride ions deplete completely near the electrode surface. The moment of the inflection point, also known as the transition time, is a function of the chloride ion concentration and is described by the Sand equation. It is shown that the square root of the transition time is linearly proportional to the chloride ion concentration. Drift in the response over two weeks is negligible: 59muM/day when measuring 1mM of Cl(-) ions using a 10Am(-2) current pulse. The transition time at a specific ion concentration can be tuned by the applied current pulse, e.g., in a solution containing 5mM chloride ions, the transition times with current pulses of 10 and 20Am(-2) are 1.56 and 0.25s, respectively. The moment of inflection determines the response, and thus is independent of the absolute potential of reference electrode. Therefore, any metal wire can act as a pseudo-reference electrode, enabling this approach for long-term and integrated-sensor applications such as measurement inside concrete structures.
AB - Ion selective electrodes (ISE) are used extensively for the potentiometric determination of ion concentrations in electrolytes. However, the inherent drift in these measurements and the requirement of a stable reference electrode restrict the feasibility of this method for long-term in-situ applications. This work presents a chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode for measuring chloride ion concentration. An anodic current pulse is applied to a Ag/AgCl working electrode which initiates a faradaic reaction that depletes the chloride ions near the electrode surface. The rate of change in potential at the Ag/AgCl electrode, due to chloride ion depletion, reaches an inflection point once the chloride ions deplete completely near the electrode surface. The moment of the inflection point, also known as the transition time, is a function of the chloride ion concentration and is described by the Sand equation. It is shown that the square root of the transition time is linearly proportional to the chloride ion concentration. Drift in the response over two weeks is negligible: 59muM/day when measuring 1mM of Cl(-) ions using a 10Am(-2) current pulse. The transition time at a specific ion concentration can be tuned by the applied current pulse, e.g., in a solution containing 5mM chloride ions, the transition times with current pulses of 10 and 20Am(-2) are 1.56 and 0.25s, respectively. The moment of inflection determines the response, and thus is independent of the absolute potential of reference electrode. Therefore, any metal wire can act as a pseudo-reference electrode, enabling this approach for long-term and integrated-sensor applications such as measurement inside concrete structures.
KW - EWI-24685
KW - IR-90573
KW - METIS-304078
U2 - 10.1016/j.aca.2014.03.013
DO - 10.1016/j.aca.2014.03.013
M3 - Article
SN - 0003-2670
VL - 821
SP - 81
EP - 88
JO - Analytica chimica acta
JF - Analytica chimica acta
ER -