A new hyphenated method utilizing FT-IR-attenuated total reflection (ATR) and electrochemical impedance spectroscopy (EIS) is presented to correlate the water uptake with concomitant potential and impedance changes of polymeric coated-wire electrodes (CWEs) and solid-contact ion-selective electrodes (SCISEs). The Ca2+-selective silicone rubber (RTV 3140) based SCISEs with poly(3-octylthiophene) (POT) as the solid-contact (SC) showed good correlation between a very low water content at the Pt-coated ZnSe substrate/SC interface and a superior potential stability. This is due to the hydrophobicity of both RTV 3140 and POT and the approximately 2 orders of magnitude lower water diffusion coefficients in POT compared to RTV 3140. Practically no potential drift could be observed during 24 h when unconditioned CaSCISEs were contacted with 10-3 M CaCl2, in contrast to the Ca 2+-selective CWEs with considerably higher water uptake and potential drift. The CaSCISEs had a fast Nernstian response with a detection limit of 8 × 10-9 M Ca2+ and a good reproducibility and stability of the standard potential, which indicates that the CaSCISEs does not require any conditioning prior to use.
ASJC Scopus subject areas
- Analytical Chemistry