Selectivity coefficients coated-wire electrodes

Selectivity Coefficients, k °j, for the Coated Wire Electrodes Compared to Those for the... 

Acetylcholineesterase Enzyme was covalently immobilized on a bovine serum albumin-modified H +-selective coated wire electrode. The sensor was used in 5mM phosphate buffer pH 7 at 30°C. The response time was 3-10 min for O.l-lOmM ACh. pH change of 6-8 had little effect. Coefficient of variation was 5.7 and 5.8%. [72]... 

Many of the ions listed in Table 5 are indicated by the corresponding coated wire electrodes exactly according to the Nernst equation in the concentration range 10" to 10" M. For sulfate and oxalate anions a slope of about 28 mV per power of ten in activity results at 25°C. Table 5 illustrates the good selectivity behavior of these electrodes. In all cases the selectivity coefficients are more favorable than those for the corresponding liquid membrane electrodes [150]. The response time is very short — only a few seconds. The lifetime of these microelectrodes is claimed to exceed 3 months. 

A 14-crown-4 derivative has also been incorporated in a PVC membrane to construct a coated-wire lithium ion-selective electrode used for the determination of lithium in blood sera, after on-line dialysis separation in a FIA system [6]. An estimation of the overall selectivity of the method over the sodium content, including that of the dialysis membrane and the electrode, resulted in a selectivity coefficient k of 1/50. This selectivity is not sufficient to overcome interferences from relatively large fluctuations in sodium contents, and corrections based on a simultaneous evaluation of the sodium content are required under such circumstances. 

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