Journal
ACS SENSORS
Volume 1, Issue 1, Pages 48-54Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acssensors.5b00015
Keywords
local acidification; anion-selective electrode; freshwater; nitrite; phosphate
Funding
- Swiss National Science Foundation (FNS Sinergia) [CRSII2-147654]
- EU Seventh Framework Program (SCHeMA project) [FP7-OCEAN 2013.2, 614002]
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The work dramatically improves the lower detection limit of anion selective membranes at environmental pH by using local acidification to suppress hydroxide interference at the membrane surface. Three separate localized acidification strategies are explored to achieve this, with ionophore-based membrane electrodes selective for nitrite and dihydrogen phosphate as guiding examples. In a first approach, a concentrated acetic acid solution (ca. 1 M) is placed in the inner filling solution of the PVC-based membrane electrode, forcing a significant acid gradient across the membrane. A second strategy achieves the same type of passive acidification by using an external proton source (fast diffusive doped polypropylene membrane) placed in front of a potentiometric solid contact anion selective electrode where the thin layer gap allows one to observe spontaneous acidification at the opposing detection electrode. The third approach shares the same configuration, but protons are here released by electrochemical control from the selective proton source into the thin layer sample. All three protocols improve the limit of detection by more than 2 orders of magnitude at environmental pH. Nitrite and dihydrogen phosphate determinations in artificial and natural samples are demonstrated.
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