Bi-enzyme sensor based on thick-film carbon electrode modified with electropolymerized tyramine

Bi-enzyme sensor based on thick-film epoxy-carbon electrode modified with polytyramine has been developed and examined for the determination of peroxidase substrates and cholinesterase inhibitors. Polytyramine was obtained on the electrode surface by repeated scanning of the potential from +600 to +1800 mV vs. Ag/AgCl in tyramine solution. The enzymes were immobilized in the polytyramine matrix by cross-linking with glutaraldehyde. The biosensor developed provides a reliable and inexpensive way for preliminary testing of common environmental pollutants with a single sensor in accordance with assumed toxic effect by the choice of appropriate substrate and measurement conditions. The bi-enzyme sensor makes it possible to determine substituted phenols and aromatic amines in the micromolar range of their concentrations and anticholinesterase pesticides with detection limits of 0.1 (Coumaphos) and 0.03 μmol l-1 (Chloropyrifos-methyl). © 2004 Published by Elsevier B.V

Voltammetric determination of sterically hindered phenols in surfactant-based self-organized media

Tert-butylhydroquinone (TBHQ), butylhydroxyanisole (BHA), and butylhydroxytoluene (BHT) are irreversibly oxidized on a glassy-carbon electrode in a medium of acetonitrile-Britton-Robinson buffer solution (1: 9, pH 3.0) at 0.61, 0.79, and 1.1 V, respectively, to give quinones. Micellar media of Triton X100,Brij® 35, and sodium dodecyl sulfate affect their oxidation. The splitting and suppression of the oxidation steps for sterically hindered phenols (SHP) is observed in the presence of nonionic surfactants. Sodium dodecyl sulfate considerably enhances anodic currents and also shifts positive potentials to lower values. The conditions of the differential-pulse voltammetric determination of SHP in a 0.1 M sodium dodecyl sulfate supporting electrolyte are found. The calibration graphs are linear in the ranges 2.02-1010, 2.34-1170, and 6.15-615 μM and the detection limits (S/N = 3) are 0.23, 0.18, and 3.5 μM for TBHQ, BHA, and BHT, respectively. The possibility of determining SHP in TBHQ-BHT and BHA-BHT mixtures in wide ranges of component concentration is demonstrated. A method is developed for the extraction-voltammetric determination of BHT in vegetable oils. © 2014 Pleiades Publishing, Ltd

Chronoamperometric determination of synthetic phenolic antioxidants in Brij® 35 micellar medium

© 2015, Pleiades Publishing, Ltd. tert-Butylhydroquinone (TBHQ) and tert-butylhydroxyanisole (BHA) are oxidized on a glassy carbon electrode modified with multiwalled carbon nanotubes in a 0.1 M LiClO4 supporting electrolyte in the medium of 1 mM Brij®35 at 0.27 and 0.47 V, respectively. A method for their chronoamperometric determination is developed. It is shown that a steady-state electrolysis is achieved within 100 s. The analytical range is 2.50–1000 µM for TBHQ and 1.50–100 and 250–1000 µM for BHA with the detection limits (S/N = 3) 0.64 and 0.38 µM, respectively. The relative standard deviation in the determination of TBHQ and BHA in model solutions does not exceed 6%. The method was tested on micellar extracts of linseed oils. The accuracy measure is 100 ± 1%, which points to the absence of matrix effects in the determination of TBHQ and BHA

Simultaneous determination of TBHQ and BHA on a MWNT-Brij® 35 modified electrode in micellar media

© 2015 The Royal Society of Chemistry. A voltammetric method for the simultaneous detection and quantification of tert-butylhydroquinone (TBHQ) and butylated hydroxyanisole (BHA) was developed using a multi-walled carbon nanotube (MWNT)-Brij® 35 modified glassy carbon electrode in Brij® 35 micellar medium. Significant improvements of TBHQ and BHA voltammetric characteristics were observed on the modified electrode. Electrochemical oxidation of TBHQ and BHA is a diffusion-controlled process that is confirmed by the linear dependence of peak currents on υ1/2 with R2 = 0.9983 and 0.9901, respectively, and involves two electrons corresponding to the formation of p-quinones. Under conditions of differential pulse voltammetry, a linear dynamic range of 1.0-1000 μmol L-1 for TBHQ and 0.50-7.50 and 10.0-750 μmol L-1 for BHA were obtained with the detection limits of 0.26 and 0.15 μmol L-1, respectively. The approach developed was successfully applied for the quantification of TBHQ and BHA in linseed oil samples with recoveries from 99% to 103% after a simple and rapid extraction with Brij® 35 micellar medium

Cholinesterase sensors based on thick-film graphite electrodes for the flow-injection determination of organophosphorus pesticides

Flow cholinesterase sensors based on planar thick-film graphite electrodes and immobilized preparations of acetyl- and butyrylcholinesterase with various activities were developed. Analytical parameters of the determination of organophosphorus pesticides depend on hydrophilic-hydrophobic interactions at the membrane-solution interface. When passing from the steady-state to flow-injection conditions of signal measurements, the limits of detection of coumaphos and chlorpyrifos-methyl decrease by a factor of 5-8, while the limit of detection of hydrophilic trichlorfon increases by a factor of 3-4. The cholinesterase sensors developed in his work can measure the concentrations of pesticides in a continuous mode for 8-12 h with the throughput of up to 5-6 measurements per hour

Comparative investigation of electrochemical cholinesterase biosensors for pesticide determination

A number of potentiometric biosensors based on cholinesterases from various sources have been developed and examined for the determination of Co- Ral and Trichlorfon to establish factors affecting the analytical performance of biosensors. Acetylcholinesterase (AChE) from electric eel and butyrylcholinesterase (BChE) from horse serum were immobilised on the surface of antimony electrode and on the commercial membranes (nylon and cellulose nitrate) by treatment with glutaraldehyde in vapours and aqueous solution. The biosensors developed make it possible to determine Trichlorfon and Co-Ral with detection limits 0.01 and 0.02 mg l-1, respectively. As shown, inert peptide or the polymer present in the membrane provide better sensitivity and lower detection limits of pesticides due to the hampering of the transfer of the product of enzymatic reaction between the membrane and the solution. The influence of the immobilisation procedure depends on the hydrophobicity of pesticide to be determined. The present comparative study reveals the importance of the enzyme matrix on the analytical performance of biosensors developed for inhibitor determination

АМПЕРОМЕТРИЧЕСКОЕ ОПРЕДЕЛЕНИЕ МОЧЕВОЙ КИСЛОТЫ, КРЕАТИНИНА И ХОЛЕСТЕРИНА НА ПЛАНАРНЫХ ЭЛЕКТРОДАХ, МОДИФИЦИРОВАННЫХ ЧАСТИЦАМИ ЗОЛОТА, В ПРОТОЧНО-ИНЖЕКЦИОННОЙ СИСТЕМЕ

A method of amperometric determination of uric acid (UA), creatinine (Cr) and cholesterol (CHO) on planar carbon electrodes (PE) modified by gold particles in a flow-injection system has been developed. PE with immobilized gold particles (Au-PE) is catalytically active with respect to UA, Cr and CHO. A multiple current increase at modifier oxidation potentials and an oxidation potential decrease of the organic compound as compared to the unmodified electrode during their electrooxidation on Au-PE was observed. The effect of the electrochemical and hydrodynamic parameters of the flow-injection system on the analytical signal was estimated for each compound. The working conditions (applied potential and flow rate) for the maximum analytical signal registration at the modified electrode for the studied biologically active compounds (BAC) were selected. With the joint presence of the considered BAC, the dependence graphs of the current on the analyte concentration in logarithmic units were linear in the range from 5x10-9 to 5x10-3 mol/l for UA, from 5x10-7 to 5x 0-3 mol/l for Cr and from 5x10-8 to 5x10-3 mol/l for CHO. Using the two-detector flow system and double planar electrodes (DPE) modified with gold particles (Au-DPE) allowed the simultaneous determination of the considered BAC. The proposed method was used to determine UA, Cr and CHO in the urine.Keywords: electrooxidation of uric acid, creatinine and cholesterol, modified planar electrode, gold particles, amperometric determination, flow-injection analysisDOI: http://dx.doi.org/10.15826/analitika.2019.23.3.005(Russian)L.G. Shaidarova, I.A. Chelnokova, I.A. Abzalova, A.V. Gedmina, G.K. Budnikov  Kazan (Volga region) Federal University (KFU), ul. Kremlyovskaya, 18, Kazan, 420008, Russia FederationРазработан способ амперометрического определения мочевой кислоты (МК), креатинина (Кр) и холестерина (ХС) на планарных углеродных электродах (ПЭ), модифицированных частицами золота, в проточно-инжекционной системе. ПЭ с иммобилизованными частицами золота (Au-ПЭ) каталитически активными по отношению к МК, КР и ХС. При их электроокислении на Au-ПЭ наблюдается многократное увеличение тока при потенциалах окисления модификатора и уменьшение потенциала окисления органического соединения по сравнению с немодифицированным электродом. Для каждого соединения оценено влияние электрохимических и гидродинамических параметров проточно-инжекционной системы на величину аналитического сигнала. Подобраны рабочие условия (налагаемый потенциал и скорость потока) регистрации максимального аналитического сигнала на модифицированном электроде для изучаемых биологически активных соединений (БАС). При совместном присутствии рассматриваемых БАС графики зависимости величины тока от концентрации аналитов, представленные в логарифмических единицах, линейны в диапазоне от 5×10-9 до 5×10-3 моль/л для МК, от 5×10-7 до 5×10-3 моль/л для Кр и от 5×10-8 до 5×10-3 моль/л для ХС. Использование двухдетекторной проточной системы и двойных планарных электродов (ДПЭ), модифицированных частицами золота (Au-ДПЭ), позволило провести одновременное определение МК, Кр и ХС. Предложенный способ был использован для их определения в урине.Ключевые слова: электроокисление мочевой кислоты, креатинина и холестерина, модифицированный планарный электрод, частицы золота, амперометрическое определение, проточно-инжекционный анализDOI: http://dx.doi.org/10.15826/analitika.2019.23.3.00

Вольтамперометрическое и последовательное инжекционное амперометрическое определение витаминов группы B на электродах, модифицированных бинарными системами на основе оксидов марганца, висмута и золота

It was found that oxides of manganese (MnOx), bismuth (ВiOx), gold (AuOx), and ВiOx–MnOx and MnOx–AuOx binary systems electrodeposited on the surface of planar carbon electrodes (SPE) exhibited catalytic activity during electrooxidation of thiamine, riboflavin, pyridoxine and cyanocobalamin in acidic media. Immobilization of the binary systems on the surface of the SPE working electrode allowed to achieve a joint selective voltammetric determination of two-component systems of the vitamins considered: riboflavin and pyridoxine on SPE with BiOx–MnOx (ВiOx–MnOx–SPE) and MnOx–AuOx (MnOx–AuOx–SPE); and riboflavin and thiamine or riboflavin and cyanocobalamin on MnOx–AuOx–SPE. The calibration dependences obtained for the considered vitamins using voltammetry on BiOx–MnOx–SPE and MnOx–AuOx–SPE electrodes were observed in the range from 1×10–6 to 1×10–3 M. Detection limit of thiamine, pyridoxine and cyanocobalamin was decreased by an order of magnitude compare to static conditions in a sequential injection system (SI-system). To implement two- and three-component analysis of biologically active additives (BAA) and drugs in the SI-system, the surface of the working electrode modified with MnOx–AuOx binary system was covered with poly-2-vinylpyridine (PVP) or Nafion (Nf) polymer films. SPE with two working electrodes (DSPE) modifies with MnOx–AuOx were used in the two-component analysis of BAA samples. PVP film was deposited on the electrode for thiamine determination and Nf film was deposited on the electrode for pyridoxine determination. Combination of SPE and DSPE with polymer composites containing MnOx–AuOx binary system and PVP or Nf in a two-detector SI-system made it possible to implement a three-component analysis of drugs containing thiamine, pyridoxine and cyanocobalamin. Excipients present in them did not interfere with the results of the determination. Application of the proposed SI-system scheme increased selectivity, speed and productivity of the analysis to 540 determinations per hour.Keywords: modified electrodes, manganese oxide, bismuth oxide, gold oxide, electrooxidation of B group vitamins, sequential injection analysis, amperometric detector.Определили, что электролитические осадки оксидов марганца (MnOx), висмута (ВiOx), золота (AuOx) и бинарных систем ВiOx-MnOx и MnOx-AuOx каталитически активны при электроокислении тиамина, рибофлавина, пиридоксина, цианокобаламина в кислой среде. Иммобилизация бинарных систем на поверхность рабочего электрода планарных углеродных электродов (ПЭ) позволила добиться совместного селективного вольтамперометрического определения в двухкомпонентных системах рассматриваемых витаминов: рибофлавина и пиридоксина – на ПЭ с ВiOx-MnOx (ВiOx-MnOx-ПЭ) и MnOx-AuOx (MnOx-AuOx-ПЭ), а рибофлавина и тиамина или рибофлавина и цианокобаламина на MnOx-AuOx-ПЭ. Градуировочные зависимости, полученные для рассматриваемых витаминов в условиях вольтамерометрии на электродах ВiOx-MnOx-ПЭ и MnOx-AuOx-ПЭ, наблюдали от 1×10-6 до 1×10-3 М. По сравнению со статическими условиями в последовательной инжекционной системе (ПослИ-системе) добились снижения предела обнаружения на один порядок для тиамина, пиридоксина и цианокобаламина. Для реализации двух- и трехкомпонентного анализа биологически активных добавок (БАД) и лекарственных средств в ПослИ-системе поверхность рабочего электрода с бинарной системой MnOx-AuOx покрывали полимерными пленками из поли-2-винилпиридина (ПВП) или нафиона (НФ). При двухкомпонентном анализе БАД использовали ПЭ с двумя рабочими электродами (ДПЭ) с MnOx-AuOx и нанесеннойпленкой из ПВП на один из рабочих электродов для определения тиамина и пленкой из НФ на другой – для определения пиридоксина. Сочетание ПЭ и ДПЭ с полимерными композитами, содержащими бинарную систему MnOx-AuOx и ПВП или НФ, в двухдетекторной ПослИ-системе позволило реализовать трехкомпонетный анализ лекарственных средств, содержащих тиамин, пиридоксин и цианокобаламин. Вспомогательные компоненты, содержащиеся в них, не оказывали мешающего влияния на результаты определения. Использование предложенной схемы ПослИ-системы повысило селективность, экспрессность и производительность анализа до 540 определений/час. Ключевые слова: модифицированные электроды, оксиды марганца, висмута, золота, электроокисление витаминов группы B, последовательная инжекционная система, амперометрический детектор

Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at s=0.9\sqrt{s}=0.9, 2.76 and 7 TeV

Measurements of the sphericity of primary charged particles in minimum bias proton--proton collisions at $\sqrt{s}=0.9$, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is linearized to be collinear safe and is measured in the plane perpendicular to the beam direction using primary charged tracks with $p_{\rm T}\geq0.5$ GeV/c in $|\eta|\leq0.8$. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity ($N_{\rm ch}$) is reported for events with different $p_{\rm T}$ scales ("soft" and "hard") defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low $N_{\rm ch}$, whereas the event generators show the opposite tendency. The combined study of the sphericity and the mean $p_{\rm T}$ with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16, published version, figures from http://aliceinfo.cern.ch/ArtSubmission/node/308

Charge separation relative to the reaction plane in Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}}= 2.76 TeV

Measurements of charge dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudo-rapidity range $|\eta| < 0.8$ are presented as a function of the collision centrality, particle separation in pseudo-rapidity, and transverse momentum. A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed, which shows little or no collision energy dependence when compared to measurements at RHIC energies. This provides a new insight for understanding the nature of the charge dependent azimuthal correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286