Registration of small (below 1%) changes of calcium ion concentration in aqueous solutions and in serum by the constant potential coulometric method

Constant Potential Coulometric Measurements with Ca2+-Selective Electrode: Analysis Using Calibration Plot vs. Analysis Using the Charge Curve Fitting

“…The results of this study are in line with similar studies aimed at exploring the possibility of analysis under constant potential coulometry mode. This new method is especially promising when small changes of the analyte concentration must be registered [ 7 , 8 , 11 , 12 , 13 ]. It is therefore important that both techniques compared here delivered good results when the ratio of the final and the initial concentration values were relatively small.…”

“…The polyethylenedioxythiophene (PEDOT) layer on the surface of GC electrodes was formed by galvanostatic electropolymerization from solution containing 0.01 M EDOT and 0.1 M NaPSS in mixed aqueous-acetonitrile (9:1 v / v ) solvent, as described elsewhere [ 7 ]. The estimated polymerization charge was 2.4 mC, and the estimated film thickness was 0.5 µm.…”

“…Chronoamperometric/coulometric measurements were performed with a time resolution of 0.03 s, by additions of suitable aliquots of CaCl 2 to the initial solution 0.25 mM aqueous CaCl 2 . For the improvement of the signal-to-noise ratio, the procedure of the chronoamperometric measurements was performed as described elsewhere [ 7 ]. The measurements were carried out at 20 ± 1 °C.…”

“…Originally, the features of the method were studied with K + -selective ISEs as a model system [ 1 , 2 , 3 , 4 ]. Further studies showed that this method can be used for quantification of divalent cations Ca 2+ , Pb 2+ , and Cu 2+ [ 5 , 6 , 7 ], and NO 3 − , SO 4 2− , and ClO 4 − anions [ 8 , 9 ]. The main advantage of the constant potential coulometry when compared with potentiometry is its ability to register small changes of target ion concentration.…”

“…The constant potential coulometry method allows for overcoming this limitation. It was reported on registration of small changes of ion concentration, below 1%, which is especially attractive for practical applications [ 7 , 10 ]. An important modification of the approach was proposed by Bakker’s group: use of an electronic capacitor in series with the electrode [ 11 , 12 , 13 ].…”