Substituted metalloporphyrin derivatives as anion carrier for PVC membrane electrodes

Potentiometric Solid-Contact Ion-Selective Electrode for Determination of Thiocyanate in Human Saliva

A new solid-contact potentiometric ion-selective electrode for the determination of SCN- (SCN-ISE) has been described. Synthesized phosphonium derivative of calix[4]arene was used as a charged ionophore. The research included selection of the ion-selective membrane composition, determination of the ISEs metrological parameters and SCN-ISE application for thiocyanate determination in human saliva. Preparation of the ISEs included selection of a plasticizer for the ion-selective membrane composition and type of the electrode material. The study was carried out using ISE with liquid internal electrolyte (LE-ISE) and solid-contact electrodes made of glassy carbon (GC-ISE) and gold rods (Au-ISE). The best parameters were found for GC sensors for which the ion-selective membrane contained chloroparaffin as a plasticizer (S = 59.9 mV/dec, LOD = 1.6 ´ 10-6 M). The study of potentiometric selectivity coefficients has shown that the thiocyanate-selective sensor could be applied in biomedical research for determination of SCN- concentration in human saliva. The accuracy of the SCN- determination was verified by testing 59 samples of volunteers' saliva by potentiometric sensors and UV-Vis spectrophotometry as a reference technique. Moreover, SCN- concentrations in the smokers' and non-smokers' saliva were compared. In order to investigate the influence of various factors (sex, health status, taken medications) on the thiocyanate level in the saliva, more extensive studies on a group of 100 volunteers were carried out. Additionally, for a group of 18 volunteers, individual profiles of SCN- concentration in saliva measured on a daily basis for over a month were collected.

Determination of trace thiocyanate with nano-silver coated multi-walled carbon nanotubes modified glassy carbon electrode

Novel nano-silver coated multi-walled carbon nanotube composites were prepared and used to fabricate a modified electrode. The application of the nano-silver coated multi-walled carbon nanotube composites modified electrode for determination of trace thiocyanate is demonstrated for the first time. The influence of substrate, pH and interference of coexisting substances was investigated for response properties of the electrode. There was a linear relationship at the range 2.5 x 10(-9) to 5 x 10(-8) mol L(-1) and 5 x 10(-8) to 1 x 10(-6) mol L(-1) of thiocyanate with the decrement of anodic DPV peak currents. The limit of detection was 1 x 10(-9) mol L(-1)(S/N=3). The constructed electrode showed excellent reproducibility and stability. Actual urine and saliva samples of smoker and non-smoker were analyzed and satisfactory results were obtained. This method provides a new way to construct any electrode for biological and environmental analysis.

Novel bilirubin-based PVC calcium sensors

Poly(vinyl chloride) membrane sensors for Ca(II) ions were constructed based on bilirubin (1,3,6,7-tetramethyl-4,5-dicarboxyethy-2,8-divinyl-[b-13]-dihydrobilenone) as a neutral carrier in the presence of various plasticizers (o-nitrophenyloctyl ether, dioctyl phethalate and dibutyl sebacate), which were used as solvent mediators to incorporate the carrier into the membranes. The role of plasticizers as a medium of complexation was demonstrated. The influences of an anionic excluder, the pH and foreign ions were investigated. The selectivity coefficients were measured by a separate solution method. Among the plasticizers used, o-nitrophenyloctyl ether gave the best selectivity in the presence of large concentrations of alkali and alkaline earth's metal ions. Using sensor number I, a linear calibration graph with a good Nernstian slope of 29.5 +/- 0.8 mV was obtained for Ca(II) concentrations of 5 x 10(-7)-10(-2) mol l(-1) with a detection limit of 3 x 10(-7) mol l(-1) (12 ppb). The sensor can be used for more than 3 months with good reproducibility and a fast response time of 10 s. The developed sensor has been successfully applied to the analysis of some pharmaceutical formulations, baby-food products and human plasma. Moreover, it can be used as an indicator sensor in the potentiometric titration of Ca(II) with EDTA.