Microbial electrode sensor for vitamin B12

A microbial sensor consisting of immobilized Escherichia coli 215 and an oxygen electrode is described for the determination of vitamin B₁₂. When the sample solution is injected into the microbial electrode system, the increased consumption of oxygen by the micro-organisms causes a decrease in the dissolved oxygen around the porous membrane of the oxygen electrode and the current decreases gradually with time until a steady state is reached. The response time for a rate measurement is 2 h. When 0.5 mg of Escherichia coli 215 is immobilized, a linear relationship is obtained between the current decrease and the vitamin B₁₂ concentration between 5 × 10^?9 and 25 × 10^?9 g ml^?1.     

Salicylate Ion‐Selective Electrode Based on a Calix[4]arene as Ionophore

A salicylate‐selective electrode based on calix[4]arene derivative was developed and its response characteristics were investigated. The optimum membrane composition was 1 % ionophore, 30 % PVC, 69 % DOS. The electrode exhibited a Nernstian slope of 58.8±0.5 mV/pSal in the range of 1.0×10^?5–1.0×10^?1 M with a detection limit of 4.3×10^?6 M at pH 4.0, 20±1 °C. The potentiometric response of the electrode in the presence of different anions was investigated by the separate solution method. The lifetime was found at least 4 months, and its response time was 5–10 s. It was successfully used for the potentiometric determination of salicylate in pharmaceutical preparations.     

Electrochemical determination of tryptophan based on silicon dioxide nanopartilces modified carbon paste electrode

Silicon dioxide nanoparticles modified carbon paste electrode was fabricated and used for electrochemical investigation of tryptophan. Compared with the unmodified electrode, the peak current significantly increased. Experimental conditions for tryptophan determination were optimized. Linear relationship between the peak current and tryptophan concentration was obtained in the range of 1.0 × 10^?7?5.0 × 10^?6 mol L^?1 and 5.0 × 10^?6?5.0 × 10^?5 mol L^?1 with an estimated detection limit of 3.6 × 10^?8 mol L^?1 (S/N = 3). Tryptophan in pharmaceutical and human serum samples were successfully determined by the proposed method.     

Application of Tetra Cyclohexyl Tin(IV) as an Anionic Carrier for the Construction of a New Salicylate Membrane Sensor

A new tin complex namely tetracyclohexyl tin(IV) (TCHT) was synthesized and used as the ion carrier for the construction of a highly selective salicylate sensor. This sensor shows a Nernstian response to salicylate ions over a very wide concentration (1.0 × 10^?7–1.0 × 10^?1 M) in a pH range of 5.5–10.5. The optimum selectivity and response could be obtained for a membrane incorporating 30% PVC, 61% BA, 3% of cationic additive (HTAB) and 6% of TCHT. The response time of the electrode is very short in the whole concentration range (15 s). The electrode also shows an excellent discriminating ability for salicylate ions with respect to the most common organic and inorganic anions including chloride, sulfate, nitrate, nitrite, cyanide, sulfite, iodide, thiocyanate, phosphate, acetate, oxalate, citrate, and tartarate ions. The detection limit of the proposed sensor is 8.0 × 10^?8 M. The electrode was successfully used for determining the concentration of salicylate ion in synthetic serums.     

Construction and analytical applications of an improved liquid-membrane electrode for salicylate

The construction and analytical applications of an improved liquid-membrane electrode for salicylate are described. Tests of various combinations of symmetrical tetraalkylammonium salicylates and solvents showed that the best liquid ion-exchanger was tetraoctylammonium salicylate in p-nitrocumene. Electrode response is Nernstian down to 2 × 10^?5 M. Major interferences are perchlorate and periodate; the working pH range is 6–9. The electrode is useful for direct potentiometric determinations of salicylate in pharmaceutical preparations.     

Mediated amperometric biosensor for hypoxanthine based on a hydroxymethylferrocene-modified carbon paste electrode

An amperometric enzyme electrode for the determination of hypoxanthine in fish meat is described. The hypoxanthine sensor was prepared from xanthine oxidase immobilized by covalent binding to cellulose triacetate and a carbon paste electrode containing hydroxymethylferrocene. The xanthine oxidase membrane was retained behind a dialysis membrane at a carbon paste electrode. The sensor showed a current response to hypoxanthine due to the bioelectrocatalytic oxidation of hypoxanthine, in which hydroxymethyiferrocene served as an electron-transfer mediator. The limit of detection is 6 × 10^?7 M, the relative standard deviation is 2.8% (n=28) and the response is linear up to 7 × 10^?4 M. The sensor responded rapidly to a low hypoxanthine concentration (7 × 10^?4 M), the steady-state current response being achieved in less than 1 min, and was stable for more than 30 days at 5 ° C. Results for tuna samples showed good agreement with the value determined by the conventional method.     

基于酞菁铜衍生物为载体的电极对水杨酸根的选择性电位响应

本文以2,9,16,23-四硝基酞菁铜(II) (Cu(II)TNPc) 和2,9,16,23-四氨基酞菁铜(II) (Cu(II)TAPc) 为载体制备PVC聚合膜,构建了水杨酸根选择性电极,并探讨了该电极的选择性响应性能。研究了增塑剂的性质、载体的含量及阴、阳离子添加剂对电极电位响应的影响。结果表明,基于Cu(II)TNPc为载体的PVC膜电极对水杨酸根 (Sal－) 呈现出优先选择性电位响应。具有最佳电位响应的电极的膜组成是：(w/w) 3.0% Cu(II)TNPc,67.0% o-NPOE,29.5% PVC和0.5% NaTPB。基于该组成的电极的线性响应范围为1.0×10－1－9.0×10－7 mol·L－1,检测下限为7.2×10－7 mol·L-1,斜率为－59.8±0.5 mV/decade;其响应快速,稳定性好,适宜的pH范围是3.0－7.0。并成功运用于了实际样品中水杨酸含量的测定,获得令人满意的结果。     

Membrane-dialyzer injection loop for enhancing the selectivity of anion-responsive liquid-membrane electrodes in flow systems Part 2. A selective sensing system for salicylate

An electrode-based flow-injection system suitable for the direct determination of salicylic acid is described. The system utilizez a tubular polymer membrrane electrode based on manganese(III) tetraphenylporphyrin chloride to sense salicylate ions formed in a recipient buffer solution held within the upper channel of a flow-through membrane dialyzer assembly. Samples containing salicylic acid are manually intoduced into the lower channel of the dialysis unit, in which a thin silicone rubber membrane separates the two channels. The analyte is trapped across the membrane as salicylate ions within a static layer of an appropriate recipient buffer. After a fixed trapping time, the recipient plug is flushed to the electrode in a conventional flow-injection manner. Peak potentials observed are logarithmically related to the salicylic acid concentrations in the original sample. Without the dialysis unit, the electrode response to salicylate is nearly Nernstian over the range 2 × 10^?6?10^?2 M. In the complete flow/dialysis system, near Nernstian response was achieved for 10^?4?10^?2 M salicylate with a 2-min trapping time. Detection limits can be altered by changing the trapping time. Anionic salicylate can be determined by acidifying the sample. The resulting system offers very high selectivity for salicylate (as salicylic acid) over most inorganic and organic anions normally found in blood. Preliminary studies demonstrate the practical application of this system for the determination of salicylate in serum.     

Electrochemical Evaluation of the Interaction between Avidin and Biotin at Biotinylated Polypyrrole Electrode Using a Redox Marker

The interaction between avidin and biotin was evaluated electrochemically by monitoring the change in the electrode response of redox markers. Biotin was immobilized on the electrode surface by means of the electrochemical polymerization of biotinylated pyrrole and pyrrole. When avidin was introduced onto the biotinylated polypyrrole electrode surface, the large change in the electrode response of the redox marker was detected. The fact that the change in the electrode response of a marker ion could be attributed to the electrostatic interaction between avidin on the electrode surface and the redox marker ion present in a solution was verified by replacing avidin with NutrAvidin. At a pH lower than the isoelectric point of avidin, the electrode response of ferrocyanide as an anionic marker ion increased linearly within the range of 5.0×10^?9 ?3.0×10^?8 M avidin. The relative standard deviation at 1.5×10^?8 M avidin was about 5.4% (n=5). The detection of biotin was also performed using a competitive reaction between biotin in solution and biotin that had been immobilized on the electrode surface in the form of the biotinylated polypyrrole.     

An amperometric monoamine oxidase biosensor for determining some antidepressants

An amperometric biosensor based on a platinum screen-printed electrode and immobilized monoamine oxidase is developed to determine antidepressants of different classes. Petylyl, pyrazidol, and flu-oxetine can be determined with determination limits of 8 × 10^?9, 8 × 10^?7, and 8 × 10^?10 M, respectively. A procedure is proposed for determining fluoxetine in tablets. It is shown that petylyl can be selectively determined by an immunochemical technique using the developed biosensor and immobilized antibodies in the concentration range from 1 × 10^?4 to 1 × 10^?8 M.     

A Nitric Oxide Biosensor Based on Myoglobin Adsorbed on Multi‐Walled Carbon Nanotubes

Myoglobin (Myb) of horse heart is incorporated on multi‐walled carbon nanotubes (MWNTs) and immobilized at a glassy carbon (GC) electrode surface. Its electrochemical behavior and enzyme activity are characterized by employing electrochemical methods. The results indicate that MWNTs can obviously promote the direct electron transfer between Myb and electrode, and that the Myb on MWNTs behaves as an enzyme‐like activity towards the electrochemical reduction of nitric oxide (NO). Accordingly, an unmediated NO biosensor is constructed. Experimental results reveal that the peak current related to NO is linearly proportional to its concentration in the range of 2.0×10^?7–4.0×10^?5 mol/L. The detection limit is estimated to be 8.0×10^?8 mol/L. Considering a relative standard deviation of 2.1% in seven independent determinations of 1.0×10^?5 mol/L NO, this biosensor shows a good reproducibility. The biosensor based on Myb/MWNTs modified electrode can be used for the rapid determination of trace NO in aqueous solution with a good stability, nice selectivity and easy construction.     

Ion-selective electrodes based on siderophores: Salicylate response of a ferrimycobactin membrane

Siderophores are compounds which transport iron across cell membranes; mycobactins are hydrophobic siderophores and were expected to be suitable for inclusion in the organic membrane phase of a liquid ion-exchange electrode responsive to iron(III) ions. In practice, no iron(III) response was obtained from mycobactin membranes (in a variety of solvents), but they did respond to salicylate ion with a sensitivity of 27–29 mV/decade over the range 2 × 10^?3–3 × 10^?2 mol l^?1 at pH 7. The effects of pH and interference by other anions are described and the possible mechanisms of the electrode are discussed. The selectivity of the electrode for salicylate is better than that of quaternary ammonium liquid ion-exchange electrodes.     

A Dual-Enzyme Electrode for the Determination of Flavin Adenine Dinucleotide in the Presence of Riboflavin and Flavin Mononucleotide

Abstract

An electrode method has been developed for the determination of flavin adenine dinucleotide (FAD) using a potentiometric gas sensor and commercially available enzyme preparations. The construction of the FAD-sensitive electrode is based on immobilizing alkaline phosphatase (E.C. 3.1.3.1) and adenosine deaminase (E.C. 3.5.4.4) on the sensing tip of an ammonia gas sensor. Alkaline phosphatase enzymatically catalyzes the hydrolysis of FAD to adenosine which is subsequently converted to ammonia by adenosine deaminase. The response of the dual-enzyme electrode is linear between 8 × 10^?5 M and 4 × 10^?3 M FAD with a slope of 43 mV/decade concentration at pH 8.5 and 37[ddot]C. The optimum buffer system is 0.5 M diethanolamine, 1 × 10^?3 M Tris-HCl and 1 × 10^?3 M MgCl₂. Electrodes constructed with enzymes immobilized by cross-linking with glutaraldehyde and bovine serum albumin showed longer life times than electrodes using enzymes entrapped by a dialysis membrane. The electrode is highly selective over riboflavin and flavin mononucleotide, but it does respond to other nucleotides.     

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag₂O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H₂O₂) at co-immobilized electrodes showed a linear relationship with H₂O₂ concentration over a concentration range from 6.0?×?10^?6 to 5.0?×?10^?2 mol L^?1, and a detection limit of 2.0?×?10^?6 mol L^?1 (S/N?=?3).     

Investigations on adsorption potentiometry Part I. Derivative adsorption chronopotentiometry of the iron(III)-2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol system

An electroanalytical method, based on derivative chronopotentiometry of the iron complex with 2-(5′-bromo-2′- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) accumulated adsorptively on the surface of a hanging mercury drop electrode, for determining trace iron in food has been developed. The dependences of the peak height on the dt/dE vs. E curve on the preconcentration time, preconcentration potential and electrode area are discussed. Optimum experimental conditions include 0.005 mol 1^?1 NH₃NH₄Cl, 2 × 10^?7 mol 1^?1 5-Br-PADAP and a preconcentration potential of ?0.40 V (vs. SCE). Under these conditions, the detection limit and the linear range are 2 × 10^?9 and 6.7 × 10^?9?1.7 × 10^?7 mol 1^?1, respectively. The relative standard error of the method is 1.5% for 6.7 × 10^?8 mol 1^?1 Fe(III). The method was applied to samples of microwave digested food.     

A reliable l-lactate electrode with a new membrane for enzyme immobilization for amperometric assay of lactate

Lactate oxidase from Pediococcus species can be rapidly and simply immobilized on a commercially available pre-activated membrane fixed to an amperometric probe detecting hydrogen peroxide, to provide a very sensitive practical l-lactate sensor. At 25°C, in a phosphate buffer pH 7.1, the detection limit is 1.25 × 10^?7 M, calibration is linear between 2.5 × 10^?7 and 2.5 × 10^?4 M, the response time is <2 min, and the probe can be used for hundreds of assays over several weeks. With a microprocessor-based instrument including the same type of electrode, sample injections can be made at 90-s intervals, the response being displayed after only 30 s. High selectivity is achieved because the differential measurement system continuously subtracts currents at the chosen potential arising from the presence of electroactive species. Samples (20 μl) from sera and dairy products were successfully tested without pretreatment; a relative standard deviation between 1 and 3% was routinely obtained. Correlation of the data with data obtained by the conventional spectrophotometric method was excellent.     

Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode

A novel poly(methylene blue)/graphene composite glassy carbon electrode was fabricated and the electrochemical behavior of maltol at the modified electrode was studied by cyclic voltammetry. In phosphate-buffered solution, the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of maltol. Under optimized conditions, the oxidation peak current showed a linear relationship with the concentrations of maltol in the ranges of 8.00?×?10^?7 to 4.00?×?10^?5 and 4.00?×?10^?5 to 5.40?×?10^?4 mol L^?1, with a detection limit of 6.50?×?10^?8 mol L^?1. The performance of the developed method was validated in terms of linearity (r?=?0.9981 and 0.9955), recovery (97.0?99.3 %), reproducibility (relative standard deviations?≤?3.1 %, n?=?6), and robustness. The method shows excellent sensitivity, selectivity, and reproducibility and has been successfully applied to analyzing maltol in a wide variety of food products.     

Sulfite-sensitive solvent/polymeric-membrane electrode based on bis(diethyldithiocarbamato)mercury(II)

A new solvent/polymeric-membrane electrode which exhibits significant potentiometric response toward sulfite ion in the 1 × 10_?6?1 × 10^?3 M range is described. The membrane is prepared by incorporation of neutral bis(diethyldithiocarbamato)mercury (II) in a thin film of plasticized poly (vinyl chloride). In sharp contrast to classical Hofmeister behavior, the resulting membrane displays little or no response to a wide range of anions (log K^pot_i,j ? ?4, i being sulfite) including sulfate, nitrate, nitrite, chloride, perchlorate, salicylate, and alkylsulfonates. Bromide and thiocyanate are moderate interferents, while significant response to iodide, thiosulfate, and sulfide is observed. These selectivity data, along with other response characteristics of the membrane, are used to postulate the mechanism by which the electrode responds to sulfite. Preliminary studies demonstrate that the electrode can be used in conjunction with an outer gas-permeable membrane for highly selective detection of total sulfite species in the form of sulfur dioxide.     

An Electrochemical Biosensor with Cholesterol Oxidase/ Sol‐Gel Film on a Nanoplatinum/Carbon Nanotube Electrode

The carbon nanotubes decorated nanoplatinum (CNT‐Pt) were prepared using a chemical reduction method and a novel base electrode was constructed by intercalating CNT‐Pt on the surface of a waxed graphite electrode. The results showed that the nano‐particles of platinum at a waxed graphite electrode exhibits high catalytic activity for the reduction of hydrogen peroxide. The cholesterol oxidase (ChOx), chosen as a model enzyme, was immobilized with sol‐gel on the CNT‐Pt base electrode to construct a biosensor. The current response of the biosensor for cholesterol was very rapid (<20 s). The linear range for cholesterol measurement was 4.0×10^?6 mol/L ?1.0×10^?4 mol/L with a detection limit of 1.4×10^?6 mol/L. The experiments also showed that the ChOx/sol‐gel/CNT‐Pt biosensor was sensitive and stable in detecting cholesterol in serum samples.     

Direct potentiometric titration of thiosulfate,thiourea, and ascorbic acid with lodate using an iodide ion-selective electrode

A potentiometric method has been developed for the semi-automatic direct titration of thiourea, thiosulfate, and ascorbic acid with potassium iodate in strongly acidic solutions using an iodide ion-selective electrode to monitor the reaction and locate the endpoint. The method is simple, fast, precise, and accurate. Amounts ranging from 0.15–1.5 mg of thiourea (3.9 × 10^?4–3.9 × 10^?3, M), 0.3–3.0 mg of thiosulfate (5.4 × 10^?4–5.4 × 10^?3, M), and 0.5–5.0 mg of ascorbic acid (5.7 × 10^?4–5.7 × 10^?3, M) have been determined with an average error of about 1%. The method has been applied to the determination of ascorbic acid in tablets. Results checked closely with those obtained with a standard titrimetric method.