Backside calibration chronopotentiometry: using current to perform ion measurements by zeroing the transmembrane ion flux.
A recent new direction in ion-selective electrode (ISE) research utilizes a stir effect to indicate the disappearance of an ion concentration gradient across a thin ion-selective membrane. This zeroing experiment allows one to evaluate the equilibrium relationship between front and backside solutions contacting the membrane by varying the backside solution composition. This method is attractive since the absolute potential during the measurement is not required, thus avoiding standard recalibrations from the sample solution and a careful control of the reference electrode potential. We report here on a new concept to alleviate the need to continuously vary the composition of the backside solution. Instead, transmembrane ion fluxes are counterbalanced at an imposed critical current. A theoretical model illustrates the relationship between the magnitude of this critical current and the concentration of analyte and countertransporting ions and is found to correspond well with experimental results. The approach is demonstrated with lead(II)-selective membranes and protons as dominating interference ions, and the concentration of Pb(2+) was successfully measured in tap water samples. The principle was further evaluated with calcium-selective membranes and magnesium as counterdiffusing species, with good results. Advantages and limitations arising from the kinetic nature of the perturbation technique are discussed.
Xu
Yida
Y
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Ngeontae
Wittaya
W
Pretsch
Ernö
E
Bakker
Eric
E
D002138:Calibration; D002413:Cations, Divalent / Q000032:analysis / Q000737:chemistry; D007477:Ions / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D007854:Lead / Q000032:analysis / Q000737:chemistry*; D008567:Membranes, Artificial; D008956:Models, Chemical; D011199:Potentiometry / Q000379:methods*
D002413:Cations, Divalent; D007477:Ions; D008567:Membranes, Artificial; D007854:Lead
Anal Chem. 2007 Nov 15;79(22):8705-11
17929899
Anal Chem. 2005 Dec 1;77(23):7801-9
16316191
Anal Chem. 2002 Feb 1;74(3):664-70
11838692
Talanta. 2008 May 15;75(3):629-35
18585124
Anal Chem. 2001 Jan 15;73(2):343-51
11199988
J Phys Chem B. 2008 Feb 21;112(7):2008-15
18217742
Anal Chem. 1988 May 15;60(10):1018-22
3407944
Trends Analyt Chem. 2005 Mar;24(3):199-207
16642205
Talanta. 2004 May 10;63(1):3-20
18969400
Anal Chem. 2003 Jul 1;75(13):3038-45
12964748
Anal Chem. 2001 Sep 1;73(17):4249-53
11569816
Anal Chem. 2007 Jan 15;79(2):632-8
17222030
Anal Chem. 2002 Aug 15;74(16):4027-36
12199570