Determination of calcium ion in sap using carbon nanotube-based ion-selective electrodes

A new reduced-size solid-state electrode using carbon nanotubes as the transducing layer has been developed for the direct determination of Ca 2+ in sap, overcoming problems encountered by commercial ISEs analysing real complex samples. We show that this solid-contact ISE, which can be easily miniaturized, can be used directly in diluted real samples without any other pretreatment. The performance parameters of the new ISE include a Nernstian slope and excellent stability, good coefficients of selectivity, range of linearity (10 −5 to 10 −2.5 M) and limit of detection (10 −6.2 M), thus making it an excellent tool for determining Ca 2+ in a wide range of plant species. A new solid contact ion-selective electrode for the detection of calcium in real sap samples is presented with very good short and long term stability and with short response times.