N. V. Shvedene

Determination of β-lactam antibiotics by potentiometry with ion-selective electrodes

Ion-selective electrodes for antibiotics from the penicillin series, with membranes based on three different classes of ionophores (anion exchangers, aza compounds, and metal phthalocyanines), were proposed. The electrochemical and performance characteristics of the sensors were studied and compared.

Ionic liquids based on quaternary phosphonium cation as active components of solid-state iodide selective electrode.

The two ionic liquids (ILs) which melt above room temperature were used as active components of solid-state ion-selective electrodes (ISEs). The both ILs are composed of quaternary phosphonium cation and fluorinated anion, namely bis(trifluoromethylsulfonyl)imide and hexafluorophosphate. Molten and then solidified ILs were used to cover solid-state screen printed electrodes with an ion-sensing layer. The sensors show the response towards iodide. The addition of tetrakis(tert-butyl)phthalocyaninatocobalt (III) iodide to ion-sensing composition significantly improved the operational characteristics. The resulting ISE demonstrates good sensitivity and detection limit: S=-(58.0 ± 0.8) mV/dec, C(min)=6 × 10(-5)М; response time is ca. 15s. A high selectivity towards iodide over number anions is observed. The ISE could be used for at least a month without any deterioration of signal.

Surfactant Ion Selective Membrane Electrodes

Abstract Calix[8]arene ethers, carboxylic esters having various p-substituents and acid are synthesized and studied. In a bulk membrane transport of dodecylpyridinium the better carrier is the simplest host, calix[8]arene octamethyl ether. Inversely, it is the worst carrier for dodecyltrimethylammonium; the better here is carboxy ester with adamantyl p-substituents. Various calixarenes are successfully used in plasticized membrane ion-selective electrodes (ISE) for both above ammonium and pyridinium surfactants. Operational characteristics, potentiometric selectivity and optimal membrane compositions are reported. Typical limit of detection is at the level of nx10−6 - 1x10−5 M, response time 5-10 s, and lifetime is at least 6 months. ISEs selectivity is significantly better than that of ion-association and crown-ether based electrodes.

Ionic liquids with an anion of N-lauroyl sarcosinate in membranes of ion-selective electrode

The study considers solubility in water, extractivity, and electrode properties of ionic liquids (IL), lauroyl tetrahexylammonium (THALS) and tetraoctylammonium lauroyl sarcosinate (TOALS). The values of solubility, found by potentiometry using ion-selective membranes of PVC-electrodes (ISE) have appeared to be 3.0 ± 0.4 mM and 0.011 ± 0.005 mM, for THALS and TOALS, respectively. Both IL quantitatively recover nitrophenol (99.9%) into chloroform from aqueous solutions in the pH range from 2 to 12. The application of IL as the active components of PVC-ISE enables the determination of lauroyl sarcosinate anion in the concentration range 1 × 10−2–1 × 10−4 M for THALS and 1 × 10−2–1 × 10−5 M for TOALS and the determination of mononitrophenols, 2,4-dinitrophenols and picrates (1 × 10−2 M–1 × 10−5 M). A solid-state sensor based on screen-printed electrode modified by TOALS IL has been proposed. The electrode has been used for the determination of 4-nitrophenol in the concentration range 1 × 10−2–1 × 10−5 M, the operational stability of the electrode is 10 days.

Hydrophobic ionic liquids in plasticized membranes of ion-selective eletctrodes

Ionic liquids with substituted imidazole, pyridine, and pyrrolidine cations and hydrophobic anions are studied as ionophores of PVC membranes of ion-selective electrodes plasticized with 2-nitrophenyloctyl ether. These membranes show a response to hydrophobic organic cations. In solutions of cationic surfactants, the slope of the electrode function is close to the theoretical one and the limit of detection does not exceed n × 10−6 M. Ion-selective electrodes for anions are developed using a trioctylmethylammonium salicylate ionic liquid. The electrode on its basis shows a stable potentiometric response to the salicylate anion in a wide range of concentrations and is characterized by good selectivity in the presence of foreign anions.

3-(4-Tolylazo)phenylboronic acid as the active component of polyhydroxy compounds-selective electrodes

Ionophoric, extraction, acidic and hydrophobic properties of 3-(4-tolylazo)phenylboronic acid (TAPBA) were studied. Determined Kd value equals to 36±2, pKa equals to 8.6±0.5. TAPBA extracts dobutamine from water into chloroform and transports it across a bulk chloroform membrane. The recovery is 83% (pH=7.5), the transport rate – (6.5±0.5)×10−7 mol/h. 1H and 13C NMR data confirm the formation of an 1:1 complex between arylboronic acid and catecholamine. TAPBA was used as electrode-active component of plasticized membrane electrodes with cationic and anionic responses to catecholamines and phenolic acids, respectively. For the diethyl sebacate-plasticized membrane, a slope of electrode function to dobutamine is 56±2 mV/decade; the detection limit is 1.3×10−5 mol/l; the linear range – 5×10−5–1×10−2 mol/l; the working pH-range – 4.8–7.6; the response time – 5–10 s. ISE gives incomplete cationic function to less lipophilic catecholamines. The membrane with cationic additive shows an anionic response to caffeic acid in wide pH range.

Phosphoryl containing podands as carriers in plasticized membrane electrodes selective to quaternary ammonium surfactants

Open chain polyethers with phosphoryl-containing terminal groups have been studied as carriers in plasticized membrane electrodes that are selective towards cationic surfactants. Host–guest complexation has also been studied by means of batch extraction and bulk membrane transport experiments. For the various guests, the bulk membrane (chloroform) transport rate decreases in the series tetraalkyl ammonium > alkyl pyridinium > alkyl ammonium, while the series of solvent extraction efficiency is exactly opposite; an explanation for this behaviour is proposed. The performance of electrode membranes follows the series for bulk membrane transport. Among the ISE membranes of various composition, one containing the longest (seven oxygen atoms) podand, o-nitrophenyl octyl ether (plasticizer), and sodium tetraphenyl borate (anionic additive) performs the best. The slope of the electrode function equals 58.5 mV/decade, the detection limit for dodecyltrimethylammonium is 3.2 × 10-6 M. ISE response time is 5–10 s, the working pH range is 2–11 and lifetime is at least 6 months. The electrode selectivity is significantly better than that of conventional ion-association and crown ether based electrodes.

New metalloporphyrazines as active components of membranes of anion-selective electrodes

Nickel(II), manganese(III), and magnesium(II) porphyrazines are synthesized and investigated as active electrode components of polyvinyl chloride plasticized membranes for ion-selective electrodes (ISE). The potentiometric response of membranes based on metalloporphyrazines doped with 1,3-dihexadecylimidazolium chloride (ionic additive) relative to benzylpenicillin and iodide anions is studied. It is found that the introduction of the ionic additive significantly improves the electrochemical characteristics of the ISE: the slope of the electrode function in benzylpenicillinate solutions is (58 ± 7) mV/dec and cmin = 7 × 10−5 M, and in iodide solutions, (55 ± 2) mV/dec and cmin = 6 × 10−6 M. It is shown that the ISE based on manganese(III) porphyrazine with an ionic additive can be used to determine iodide in Iodinol preparation.

Ion-Selective Electrodes Based on Adamantylcalix[4,8]arenes for the Determination of Alkali Cations

Calix[4,8]arenes bearing adamantyl substituents in the upper rim and ethoxycarbonylmethoxy groups in the lower rim of the macrocycle were proposed as ionophores in membranes of ion-selective electrodes (ISEs) for determining alkali cations. Depending on the number of phenolic fragments (n) in the calixarene molecule, ISEs respond to either sodium (n = 4) or cesium (n = 8) ions. Sensors based on membranes that, along with ionophores, contain tetraphenyl borate ions as a lipophilic additive are selective for Na and Cs ions in the presence of other alkali metals. They exhibit almost theoretical responses over the concentration range from 1 × 10–4 to 1 × 10–1 M at pH 5.5–12 for Na-SE and pH 3–11 for Cs-SE, respectively.

Binuclear Copper(II) Phthalocyanate as a Ionophore for Membrane Anion-Selective Electrodes

The use of a binuclear metal phthalocyanate as an ionophoric component of PVC membranes of ion-selective electrodes was studied. The proposed electrodes based on planar copper(II) hexa(tert-butyl)biphthalocyanate bound via a benzene ring exhibited satisfactory electrochemical properties in solutions of maleic and terephthalic acids.