Discrimination of apple juice and herbal liqueur brands with solid-state electrodes covered with polyaniline and thiacalixarenes.

Solid-contact ion-selective electrodes based on glassy carbon electrode covered with electropolymerized polyaniline and tetrasubstituted thiacalix[4]arene ionophores with hexyl and o-pyridylamido functional groups at the lower rim have been developed and examined in the discrimination of the brands of apple juices and herbal liqueurs. For this purpose, the liquids tested were diluted and spiked with a constant amount of Fe(3+) ions. The variation of the signal toward Fe(3+) ions was achieved due to their involvement in the reactions with the organic ligands and the antioxidants present. As was shown, the combination of the three electrodes with various receptors makes it possible to predict the brand of apple juices and herbal liqueurs using linear discriminant analysis in 95-100% cases. The discrimination procedure makes it possible to discriminate liquids within 20 min. Besides, the electrodes developed make it possible to detect individual antioxidants (ascorbic, malic, oxalic acids, hydroquinone, and quercetin) in the range from 5.0x10(-6) to 1.0x10(-2) M in direct potentiometric measurements and redox titration.

Selectivity of solid-contact Ag potentiometric sensors based on thiacalix[4]arene derivatives.

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.5 x 10(-8)M. The sensitivity of Ag(+) detection decreases in the following range of thiacalix[4]arene substituents: morpholide>pyrrolidide>amidopyridine>hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag(+), Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag(+) determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.

Ag selective electrode based on glassy carbon electrode covered with polyaniline and thiacalix[4]arene as neutral carrier.

Potentiometric sensor based on glassy carbon electrode covered with polyaniline and neutral carrier, e.g. thiacalix[4]arene containing pyridine fragments in the substituents in the lower rim has been developed and applied for determination of Ag(+) ions in the range from 1.0x10(-2) to 5.0x10(-7)M with the response time of 12s. The presence of thiacalixarene in the surface layer improves the reversibility and selectivity of the signal towards transient metal ions. The potentiometric selectivity coefficients were determined for various measurement conditions. As shown, the pH control and the use of NaF as a masking agent fully eliminate the interfering effect of Hg(2+) and Fe(3+) ions, respectively. The reaction of Ag(+) with thiacalixarene was proved by the investigation of the extraction of picrate complexes of transient metals in the organic phase. The potentiometric sensor developed was successfully used for the potentiometric determination of silver sulfathiazole (Argosulfantrade mark).