Poly(vinyl chloride)/Nanocarbon Composites for Advanced Potentiometric Membrane Sensor Design.

Polymer nanocomposites filled with carbon nanoparticles (CNPs) are a hot topic in materials science. This article discusses the current research on the use of these materials as interfacial electron transfer films for solid contact potentiometric membrane sensors (SC-PMSs). The results of a comparative study of plasticized poly (vinyl chloride) (pPVC) matrices modified with single-walled carbon nanotubes (SWCNTs), fullerenes-C60, and their hybrid ensemble (SWCNTs-C60) are reported. The morphological characteristics and electrical conductivity of the prepared nanostructured composite films are reported. It was found that the specific electrical conductivity of the pPVC/SWCNTs-C60 polymer film was higher than that of pPVC filled with individual nanocomponents. The effectiveness of this composite material as an electron transfer film in a new potentiometric membrane sensor for detecting phenylpyruvic acid (in anionic form) was demonstrated. Screening for this metabolic product of phenylalanine in body fluids is of significant diagnostic interest in phenylketonuria (dementia), viral hepatitis, and alcoholism. The developed sensor showed a stable and fast Nernstian response for phenylpyruvate ions in aqueous solutions over the wide linear concentration range of 5 × 10-7-1 × 10-3 M, with a detection limit of 10-7.2 M.

Potentiometric quantitation of general local anesthetics with a new highly sensitive membrane sensor.

The detection of local anesthetic drugs is of great importance in the analysis of pharmaceutical, clinical and forensic samples. This paper reports a simple and sensitive potentiometric assay suitable for detecting general local anesthetics (LAs) of two types, namely: amino ester-anesthetics (procaine) and amino amide-anesthetics (lidocaine, articaine). As a detector, a new highly sensitive sensor based on a poly(vinyl chloride)-matrix membrane incorporating ion-pair complexes of protonated procaine with 2-[bis-octadecyl-sulfonic)-closo-decaborate is used. To improve the analytical characteristics of the sensor, the tetradodecylammonium - 2-[bis-octadecyl-sulfonic)-closo-decaborate associate as a lipophilic additive is proposed. The procedures for the synthesis of both electroactive membrane components are described. The dependence of potential response characteristics of the potentiometric system on the membrane composition, local anesthetic properties, and pH of the sample solutions is discussed. The difference in sensitivity and selectivity of the sensor was found to be responsible for the lipophilic property and pKa values of local anesthetic molecules. The developed sensor exhibited a near Nernstian response to cationic forms of procaine and some other anesthetics of higher lipophility, in particular lidocaine and articaine, over a wide linear concentration range. The limit of detection was varied from 2 × 10-8 to 5 × 10-7 µM, and it is the lowest value among the early published potentiometric analogs. The proposed method was successfully applied to the analysis of pharmaceutical formulations and spiked enzyme-free urine samples containing LAs at low concentration levels (0.5-100 µg mL-1). The recovery range (n = 5) was 98.0-101.5%, and the relative standard deviation was no more than 5.0%.

A New Electrochemical Sensor for Direct Detection of Purine Antimetabolites and DNA Degradation.

The development of a reliable electrochemical sensor using a hybrid nanocomposite consisting of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) functionalized graphene oxide (GrO-IL) and gold nanoparticles (AuNPs) stabilized by chitosan (Chit) was described. The new sensor, labelled as GrO-IL-AuNPs-Chit/CSE, exhibited an improved electrocatalytic response to cancer drugs such as purine antimetabolites (6-thioguanine, 6-mercaptopurine, and azathioprine) in a wide concentration range with a low detection limit (20-40 nmol·L-1, S/N = 3), and satisfactory recoveries (97.1-103.0%). The sensor has been also successfully used for cyclic voltammetric study of a salmon sperm double-stranded DNA degradation and DNA-6-mercaptopurine interaction in aqueous solutions (pH 7.4).

Flow injection potentiometric determination of total antioxidant activity of plant extracts.

A new flow injection potentiometric (FIP) method, rapid, reproducible and simple to apply, has been developed for the in vitro evaluation of antioxidative capacity of aqueous plant extracts. This method is based on the transient negative signal measurements with a flow-type platinum electrode detector due to the composition change of a [Fe(CN)6]3-/[Fe(CN)6]4- redox-reagent solution. The variables affecting the signal height such as composition and concentration of redox-reagent, injected sample volume, flow rates of carrier and redox-reagent solution streams were studied in details and the conditions were optimized. For the compounds under study, a linear relationship was stated between the potentiometric signal height and the logarithm of antioxidant concentration. It was stated that a wide antioxidant activity range from 1 microM to 10 mM could be determined by the changing concentrations of the hexacyanoferrate(III) from 5 to 0.01 x 10(-4). The present FIP method was applied to quantify relative antioxidant activity (RAA index) of the representative water-soluble antioxidants (ascorbic acid, pyrocatechol, pyrogallol, caffeic acid, chlorogenic acid, gallic acid, tannic acid, uric acid, L-cysteine, trolox). The high sampling rate (100 h(-1)) and a satisfactory reproducibility (R.S.D.=0.7-1.8%, n=5, 0.1 mM each compound) were obtained. The method was also applied to estimate total antioxidant activity (TAA) of real samples (green and black tea infusions, herbal infusions and fresh fruit extracts) and the results were compared with those achieved using well-known in vitro testing methods.