Enzymatic Determination of Serum Adenosine-5-Triphosphate by Amperometric Measurement of the Rate of Oxygen Depletion

Abstract

ATP is determined by measuring the competition for glucose between a hexokinase-catalyzed dephospnorylation of ATP and glucose oxidase catalyzed oxidation of glucose. The ATP competition for glucose decreases the rate of oxygen consumption via the oxidation reaction, which is measured amperometrically with a Clark oxygen electrode. The decrease in the oxygen depletion is proportional to the concentration of ATP in the sample. A 10 to 50 μl sample is required and analyses are completed in 3 minutes or less.     

Maleanilic Acids as Highly Selective Reagents for the Amperometric Determination of Thorium (IV)

Abstract

Thorium has been determined amperometrically at an applied e. m. f. of -1.2V with fifteen maleanilic acids. Out of these o-tolyl, p-tolyl, 1-naphthyl, 2-naphthyland 4-amino maleanilic acid were found promising analyticalreagentsand most effective. Th(IV) in the range 6.60 to 2350.0 mg per 100 ml can be determined with an error of ± 0.2%. The interference of fifty-five ions were studied and only five ions Zn(II), Pb(II), Fe(III), UO₂ (II) and Zr(IV) interfered. which could be masked by the addition of S₂O² ₃ or SCN^?, Cl^? or SO^2- ₄, SCN^? or citrate, citrate or tartrate and P₂O^4- ₇ respectively.     

Electrochemical Oxidation and Sensitive Determination of Pyrogallol at Preanodized Screen‐Printed Carbon Electrodes

In this study, we report a simple, low‐cost and rapid electrochemical sensor based on the anodically pretreated screen‐printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow‐injection amperometric methods. A linear calibration plot was obtained for 10‐1000 μM pyrogallol with a slope of 0.0562 μA/μM. The detection limit (S/N = 3) was 0.33 μM. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.     

The electrochemical determination of phenolic derivates using multiple pulsed amperometry with graphite based electrodes

The electrochemical determinations of 4-chlorophenol (4-CP) and 4-nitrophenol (4-NP) by chronoamperometry (CA) and multiple pulsed amperometry (MPA) using expanded graphite-epoxy composite (EG-Epoxy) and rotating spectral graphite disc (SG) electrodes are reported. The electrochemical behaviours of both electrodes in the presence of organics informed about oxidation peak potential and the electrode fouling with organics concentration increasing. Setting up the oxidation peak potential as detection potential, only SG gave good electroanalytical performance using CA. However, by MPA applying both electrodes exhibited the capability to assess electrochemically and quantitatively the pollutants from aqueous solutions. UV spectrometric method detecting 4-CP and 4-NP at λ = 280 nm and λ = 398 nm wavelength, respectively was used for validation and parallel determinations.     

Electrochemical Oxidation and Sensitive Determination of Acetaminophen in Pharmaceuticals at Poly(3,4‐ethylenedioxythiophene)‐Modified Screen‐Printed Electrodes

The current study reports electrocatalytic oxidation of acetaminophen at screen‐printed electrode (SPE) modified with electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film. Cyclic voltammetric studies show that the SPE/PEDOT electrode lowers overpotentials and improves electrochemical behavior of acetaminophen (ACAP) in aqueous buffer solutions, compared to the bare SPE. Excellent analytical features are achieved, including high sensitivity, low detection limit and satisfactory dynamic range, by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and flow‐injection amperometry (FIA) under optimized conditions. The proposed methods obtain satisfactory results in detection of acetaminophen in two commercial tablets.     

Periodically interrupted amperometry at membrane coated electrodes: a simplified pulsed amperometry

Amperometric detection combined with separation technique or with selective molecular recognition step can be very effective solving quantitative analytical tasks. When the amperometric working electrode surface needs cleaning or reactivation, pulsed amperometric technique can be the choice. Coating working electrodes with different sensitizing or protecting layer is quite common in the practice of voltammetric analysis. In these studies the behavior of coated electrodes using a simplified pulsed amperometric working program which can be named periodically interrupted amperometric (PIA) detection has been investigated. Rotating platinum, and carbon paste electrodes coated with dialysis film or porcine intestinal membrane were used in the experiments. The signal in case of electrochemical oxidation of hydrogen peroxide and ascorbic acid at convective conditions has been evaluated. The signal, obtained with conventional amperometry has been compared with signal collected with a periodically interrupted amperometric measuring program, allowing time for the diffusion to reload the diffusion layer at the electrode surface. The sensitivity and the lower limit of detection (4.5 × 10⁻⁷ M for ascorbic acid and 2 × 10⁻⁶ M for H₂O₂) proved superior in case of the periodically interrupted amperometry.     

A Simple Strategy for Simultaneous Determination of Paracetamol and Caffeine Using Flow Injection Analysis with Multiple Pulse Amperometric Detection

In this work, we report a simple and novel strategy for simultaneous analysis using flow injection analysis with multiple pulse amperometric (FIA‐MPA) detection. The proposed strategy was successfully used for simultaneous determination of paracetamol and caffeine (model analytes) in pharmaceutical formulations. A sequence of potential pulses (waveform) was selected in such a way that PA is selectively oxidized at E₁ (+1.20 V/50 ms) and both compounds (PA+CA) are simultaneously oxidized at E₂ (+1.55 V/50 ms); hence, current subtraction (using a correction factor) can be used for the selective determination of CA. The proposed FIA method is simple, cheap, fast (140 injections h^?1), and present selectivity for the determination of both compounds in pharmaceutical samples, with results similar to those obtained by HPLC at a 95 % confidence level.     

Nonenzymatic dopamine biosensor based on tannin nanocomposite

A dopamine (DA) biosensor was developed based on polypyrrole/tannin/cetyltrimethylammonium bromide (PPy/TA/CTAB) nanocomposite and central composite rotatable design (CCRD) was employed for the optimization of conditions. Chemical polymerization of the PPy/TA in the presence of a cationic surfactant, CTAB, reduced the particle size of composite and a rod-like structure with a lumpy surface and high porosity was observed for nanocomposite justifying the highest current response for the modified electrode. Amperometry and differential pulse voltammetry analyses were applied for all electrochemical measurements and DA detection in the range of 0.5–100 μM. The good adhesion of nanocomposite on the electrode surface, as well as porosity and high surface area of the modified electrode, enhanced the diffusion of DA molecules inside the matrix. Amperometry analysis of the Screen printed carbon electrode/PPy/TA/CTAB modified electrode displayed a good sensitivity of 0.039 μA (μM)⁻¹ toward DA with the limit of detection of 2.9 × 10^–7 M. The modified biosensor also excludes the interfering species of ascorbic acid and uric acid which makes this sensor appropriate for DA determination. The proposed biosensor showed an acceptable reproducibility and repeatability with low relative standard deviations of 4.8% and 4.4%, respectively.     

Silver Amalgam Tubular Detector Combined with Platinum Auxiliary Electrode for Electrochemical Measurements in Flow Systems

A new type of tubular detector with platinum auxiliary electrode inside the silver amalgam tube (TD+AuxE) was proposed, fabricated, tested and compared with a typical silver amalgam tubular detector developed earlier. Non‐stop‐flow differential pulse voltammetric anodic stripping method (AS‐DPV) and amperometric method in a glucose oxidase biosensor arrangement were tested. Both detectors were applied for AS‐DPV detection in flow systems for the first time. Solutions of zinc and cadmium cations were used as the testing species for voltammetry, and detection of oxygen concentration was used for amperometry. All these experiments require application of highly negative potentials, which is possible to realize with detectors made of silver solid amalgam. The proposed combination of TD+AuxE provides a much greater current response than the arrangement with three individual electrodes. All relevant parameters were optimized for the developed TD+AuxE. The simple and fast measuring protocol for the determination of the zinc content in commercial food supplement tablets has been developed.     

Advantages of Amperometric Readout Mode of Ion‐selective Electrodes under Potentiostatic Conditions

Amperometric responses of all‐solid‐state ion‐selective electrodes, recorded under potentiostatic conditions, were studied on example of potassium‐selective sensors with polypyrrole solid contact, at potential corresponding to reduction of the solid contact material and accompanying transfer of potassium ions across the membrane. Selective and stable in time linear dependences of current vs. logarithm of analyte concentration were recorded, resulting from high membrane resistance and changing membrane potential. The influence of experimental parameters as applied potential or thickness of the membrane was discussed. Advantages of the amperometric mode compared to potentiometric one relate to possibility of tailoring analytical parameters (sensitivity, magnitude of the signal) as well as over one order of magnitude decrease of the detection limit. The latter effect is achieved due to externally forced incorporation of potassium ions from the solution to the membrane, compensating their spontaneous release to the sample solution. A method of experimental setup simplification was proposed, with application of two‐electrode system, which can be used in the absence of external polarization source. The required driving force for the current flow was assured by spontaneous oxidation process occurring at the second electrode, coupled with reduction of the solid contact material of the ion‐selective electrode. In this case also stable in time calibration plots can be recorded.