Sensors for ions in aqueous solution

Pt-electrodes coated with an electrochemically prepared 3-methylPT layer have enhanced anodic current response in cyclic voltammetry in nitrate and perchlorate aqueous solutions compared to the response in other salt solutions because of the oxidizing character of the two mentioned ions therefore 3-methylPT has been claimed as a material for sensors for oxidizing ions in aqueous solutions [203, 204]. 

Glassy carbon electrodes coated with an electrochemically prepared layer of 3-methylPT show selective response to anions with different anion radii depending on the thickness of the 3-methylPT layer thus nitrates, tetrafluoroborates, perchlorates, fluorides, primary phosphates, sulfates and tosylates can be detected [205]. 

Chemically prepared copper(II)-containing 3-methylPT pressed powder used as working electrode of a three-electrode system in a thin layer amperometric cell unit can detect ionic analytes (fluoride, chloride, nitrate, sulfate, ascorbate, oxalate, citrate, each as sodium salts) in an aqueous stream by flow-injection analysis. At applied voltages between 0.2 and 3.0 V (against Ag/AgCl) this coated electrode possesses favorable sensitivity and stability in comparison with metallic electrodes normally under use. This electrode shows no deterioration in its performance for more than a year [206]. 

Graphite electrodes were coated electrochemically with 3-methylPT, then iodine was incorporated into the polymer phase by electrochemical oxidation of iodide at a potential of -f0.70 V. This modified electrode as a potentiometric iodide ion sensor was found to be suitable for the measurement of iodide concentrations down to 10 M its selectivity coefficients for most of the potential interferents (15 anions have been studied) have been estimated to be of the order of 10 [207]. 

Platinum electrodes coated with electrochemically polymerized thiophene, 3-methyl-, 3-octylthiophene, 2,2 -bithiophene as well as 4,4 -dioctyl-2,2 -bithiophene can be used as indicator electrodes giving a cationic response to monovalent cations such as H+, Li+, Na , K , NH4 and showing some sensitivity to divalent cations such as and Ca [208]. 

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