Osmium Redox Polymer Film Electrode and Its Electrocatalytic Properties towards the Oxidation of Epinephrine: Electrochemical Quartz-Crystal Microbalance and Voltametric Characterization

An osmium redox polymer PVI-PAA-dmeOs is electrodeposited onto a gold electrode by using repetitive double potential step chronoamperometry. The resulting film is permeable to the substrates and products of the catalyzed reaction, and permits fast electron transfer. The frequency variation during the potential step process is recorded using electrochemical quartz-crystal microbalance (EQCM). A reaction mechanism for electrochemical deposition of the osmium redox polymer is proposed. The characteristics of the PVI-PAA-dmeOs film are investigated by EQCM and cyclic voltametry. The results show the hydrated osmium PVI-PAA-dmeOs film to exhibit excellent electrocatalytic activity towards the oxidation of epinephrine. At a bare gold electrode, the epinephrine oxidation current increases greatly and the oxidation peak potential negatively shifts to about 0.16 V (Ag/AgCl) at the film-modified electrode. Under optimal conditions, amperometric measurements are performed at 0.18 V and the current response of epinephrine changes linearly with its concentration from 5 × 10^?7 to 1 × 10^?4 mol l^?1. A detection limit of 1.5 × 10^?7 mol l^?1 (S/N = 3) is obtained.     

Simultaneous Detection of Peracetic Acid and Hydrogen Peroxide by Amperometry at Pt and Au Electrodes

Based on preliminary voltammetric investigations at both Pt and Au electrodes in aqueous solutions buffered at different pH values in the range 0–10, two possible profitable triple‐pulse amperometric approaches were developed for determining simultaneously peroxyacetic acid (PAA) and hydrogen peroxide present in the same samples. At both surfaces a pulsed waveform applied at rotating‐disc electrodes was adopted to take advantage on one hand of the optimized signal reproducibility achieved by this potential multistep antifouling approach and on the other hand of the constant thickness of the diffusion layer, which is necessary when the recording of time‐independent currents is desired. At a rotating‐disc Pt electrode an anodic selective signal was indeed recorded for H₂O₂ alone, while PAA contents could be inferred only from the difference of convenient signals, since at all pHs explored its sole cathodic reaction could be observed at potentials coincident with those proper for the reduction of H₂O₂ too. The same pulse approach at Au electrodes instead provided totally independent signals for the two analytes considered, thus proving to be suitable for their independent detection. In fact, H₂O₂ alone undergoes anodic oxidation also at this surface, while the reduction of PAA occurs at potentials less cathodic than those required for H₂O₂. At both electrodes, the best results turned out to be achieved at pH 0 in terms of both precision (±2–4%) and detection limits (0.2–0.3 mM), as well as of linear range which extended for about three orders of magnitude. The kinetics of the equilibrium involving the generation of H₂O₂ from the reaction of PAA with water was also evaluated, since it was suspected of making unreliable the proposed amperometric approaches.     

Evaluation of on-line preconcentration and flow-injection amperometry for phosphate determination in fresh and marine waters

Dissolved reactive phosphorus (DRP) was determined as orthophosphate (PO₄-P) in fresh and saline water samples by flow-injection (FI) amperometry, without and with in-valve column preconcentration. Detection is based on reduction of the product formed from the reaction of DRP with acidic molybdate at a glassy carbon working electrode (GCE) at 220 mV versus the Ag/AgCl reference electrode. A 0.1 M potassium chloride solution was used as both supporting electrolyte and eluent in the preconcentration system. For the FI configuration without preconcentration, a detection limit of 3.4 μg P l⁻¹ and sample throughput of 70 samples h⁻¹ were achieved. The relative standard deviations for 50 and 500 μg P l⁻¹ orthophosphate standards were 5.2 and 5.9%, respectively. By incorporating an ion exchange preconcentration column, a detection limit of 0.18 μg P l⁻¹ was obtained for a 2-min preconcentration time (R.S.D.s for 0.1 and 1 μg P l⁻¹ standards were 22 and 1.0%, respectively). Potential interference from silicate, sulfide, organic phosphates and sodium chloride were investigated. Both the systems were applied to the analysis of certified reference materials and water samples.     

A sensitive xanthine oxidase electrode with silk net for estimating fish freshness

An enzyme biosensor was constructed using a plate platinum electrode and immobilized xanthine oxidase (XOD).Only a very small quantity of enzyme was chemically immobilized on a special silk net.Hydrogen peroxide released during the enzymatic reaction was detected by the electrode at+0.65 V (vs.Ag/AgCl).The electrode was very sensitive to hypoxanthine and its detection limit was 1×10-7 mol/L.When it was applied to the determination of fish freshness,the results agreed well with those obtained by traditional methods-determination of total volatile basic nitrogen (TVB-N) and microbial count.A range for estimating the freshness of river fish was suggested.     

溅射金膜修饰玻片电极检测六价铬

采用离子溅射技术制备了一种新型金膜修饰片状玻璃电极。线性扫描伏安分析表明六价铬在该电极上具有良好的电化学响应。通过优化溅射时间、溅射电流、电解质等参数,得到线性扫描伏安法的检出限(S/N=3)为6.5μg/L,安培法的检出限为2.0μg/L。电极批间重现性为9.2%(n=10),同批次电极间的重现性为9.2%~25.8%(n=10)。该电极制备过程简单,成本低,可实现批量制备。应用该电极对塑料及湖水中的六价铬含量进行检测,结果与HPLC-ICP-MS测定值基本一致。     

Determination of Bitterness of Extra Virgin Olive Oils by Amperometric Detection

A flow injection system with amperometric detection at potentials poised at +0.4 and +0.9 V was used to evaluate intensity of the bitter taste in monovarietal Extra Virgin Olive Oils (EVOO). Results from the proposed method were based on the extraction of the bitter constituents of the virgin olive oil samples in methanol‐water, followed by the direct amperometric measurement. These potentials were selected according to the hydrodynamic voltammogram of oleuropein, one of the most prominent and bitter phenolic compound found in EVOO. The amperometric detection was applied on 32 monovariatal EVOO samples. Results were correlated with the phenolic profile measured by high performance liquid chromatography (HPLC). The amperometric signal at +0.9 V mainly correlated with the total phenols of the samples (R²=0.81), whereas the signal at +0.4 V mainly correlated with oleuropein aglycone (3,4 DHPEA‐EDA, R²=0.79). Bitterness intensity of the samples was evaluated by a trained sensory panel of experts and the results compared to those obtained by the amperometric flow system. The best correlation with the bitter taste was achieved by the sensor at +0.4 V (R²=0.72). A calibration model based on partial least squares was built with three variables, namely the sensors set at +0.4 and +0.9 V and the total phenol content of the EVOO extracts. The model showed a moderate capacity to predict the bitterness of the EVOO samples using leave one out method, (R²=0.75) and in prediction of a test set of samples (R²=0.7). Such approach is very promising for future studies.     

流动注射安培法快速测定食盐中碘

报道了在酸性溶液中 ,IO- 3可被过量的I- 还原 ,FI流动注射安培法快速测定食盐中碘的方法。溶解于蒸馏水中的食盐样品 (30 μl)注入pH 1的 0 .1mol·L- 1NaCl + 1× 10 - 3mol·L- 1KI的载液中。自行研制的壁喷玻碳电极安培流通检测池作为工作电极 ,电位为 + 0 .2V(vs.SCE)。该系统和反向 (注入KI)系统的线性范围均为 1× 10 - 6 ～ 1× 10 - 4mol·L- 1,检出限为 5× 10 - 7mol·L- 1,相对标准偏差为 0 .8% (n =37) ,样品测定的回收率为 97.6 %～ 10 4 % ,采样频率 90样·h- 1。通过Bernoull恒流瓶可获得无脉冲载流。     

Determination of Amygdalin in Blood Serum

Abstract

A rapid, simple and sensitive method for the repetitive determination of amygdalin in human serum has been developed. The method is based on the β-gluco-sidase-catalyzed hydrolysis of amygdalin to glucose, which subsequently is oxidized in the presence of glucose-oxidase. The sample is injected into a continuously circulated reagent mixture and the oxygen depletion is monitored with a three-electrode amperometric system. Amygdalin in the range 0.02 to 2 mg/ml has been determined with relative errors and relative standard deviation of about 2%. The maximum determination rate is 700 injections/h. Recovery studies are also reported for amygdalin in serum calibration and controls.     

Toxicity assessment of chlorophenols using a mediated microbial toxicity assay

While direct toxicity assessment (DTA) is now widely recognised as a useful tool for environmental risk assessment, many existing tests fail to meet end-user needs. This article describes the significant progress made to the MICREDOX® DTA assay, developed at Lincoln Ventures Ltd, brought about by miniaturising this assay to a multi-well plate format combined with limiting current microelectrode transduction. The benefits have been reduced: preparation time, reduced assay time, lower material costs and a higher level of replication achieved. To validate the precision of the miniaturised format, the concentrations required to cause a 50% decrease in signal (EC₅₀) by an archetypal group of toxicants, the chlorophenols, were determined using two terrestrial bacterial strains, Escherichia coli K12 and Klebsiella oxytoca 13183. The assay time was then reduced by stepwise adjustment of the incubation time, from 60 down to 5 min, and the EC₅₀s reported by E. coli to each of the toxicants after 45, 30, 15 and 5 min incubations were determined. The results obtained match closely with those reported by the Activated Sludge Respiration Inhibition Test and confirm the miniaturised multi-well plate MICREDOX® DTA assay reliably reports representative EC₅₀ values for these toxicants. The previously described trends of increasing toxicity with increasing chlorine substitution and the observation that meta-substituted chlorophenols are more toxic than their ortho-substituted counterparts are also confirmed. The ability to monitor toxicity using terrestrial organisms, in volumes amenable to multi-well microtitre plates and incubations requiring only a few minutes, facilitates the rapid generation of highly reproducible, easy to operate and inexpensive DTA measurements.     

Electrode Hybride Pour la Determination de Phosphates et de Polyphosphates. Application aux Problemes Lies a l'Environnement

Abstract

The determination of phosphates and polyphosphates has been effected using an hybrid electrode, which consists of a glucose oxydase enzymic membrane and a Solanum tuberosum tissue slice. This membrane, rich in acid phosphatase, catalyses the glucose-6-phosphate hydrolysis. This reaction is quantitatively inhibited by phosphate. Several factors involved in the electrode response, like substrate concentration, pH, ionic strength and type of buffer are discussed in detail. At a 4.10^?4 M glucose-6-phosphate concentration, the linear ranges of phosphates and polyphosphates are, respectively, 6.10^?5 M to 1.6.10^?3 M and 3.10^?5 M to 1.10^?3 M. The urinary phosphate contents determinated by this biosensor are in good agrement with those obtained by usual spectrophotometric techniques.