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.

p-tert-Butylcalix[4]arenes, in the cone conformation, di- and tetra-substituted at the narrow rim with charged phosphonium groups, have been synthesised and characterised. Their interactions with a wide range of anions have been investigated in chloroform and acetonitrile solutions by means of ¹H and ³¹P NMR and isothermal titration microcalorimetry. These compounds have also been incorporated as sensing material in poly(vinyl chloride) ion-selective electrodes. The results showed that they interact strongly with the more lipophilic anions Cl , SCN⁻  and I⁻ , in solution as in the electrode membranes. The origin of this selectivity is discussed and, in particular, the role of the salt counterion is examined.

The synthesis and characterization of a new tetra (triphenylphosphonium) p-tert-butylcalix[4]arene 2 is presented. Its interactions with anions were studied by ¹H and ³¹P NMR and UV absorption spectrophotometry, showing the biggest interaction with ClO₄ ⁻ , I⁻  and SCN⁻ . Anion selectivity in ion-selective PVC-membrane electrodes (ISEs) plasticized with o-NPOE containing ionophore 2 was also investigated. Compound 2 shows a potentiometric response for various anions with the following selectivity pattern: ClO₄ ⁻  > SCN⁻  > I⁻  > Cr₂O₇ ^2 −  > NO₃ ⁻  > Br⁻  > Cl⁻ .

The diethyl amides of p-tert-butyldihomooxacalix[4]arene (1), p-tert-butylhexahomotrioxacalix[3]arene (2) and p-tert-butylcalix[4]arene (3) were used as active materials in ion-selective membrane electrodes to check the detection of different kinds of cations (Na⁺, K⁺, Cs⁺, Mg^2 + , Ca^2 + , Mn^2 + , Cu^2 + , Zn^2 + , Cd^2 + , Pb^2 +  and tetramethylammonium cation). The electrode characteristics and selectivity coefficients were determined and compared. Optimisation of the PVC membrane composition was achieved using three different plasticisers (bis(2-ethylhexyl) adipate, o-nitrophenyl octyl ether and bis(2-butylpentyl) adipate). Amide 3 shows selectivity for Na⁺, whereas compounds 1 and 2 exhibit the highest selectivity for Pb^2 +  among all the studied cations. The X-ray crystal structure of dihomooxacalix[4]arene tetra(diethyl)amide (1) was determined, revealing it to be in the cone conformation.