An electrochemical alcohol sensor based on a co-electrodeposited Pt ∣ WO3 electrode

Previous studies by Tseung et al. have shown that co-electrodeposited Pt ∣ WO₃ acts as a very effective bi-functional anode catalyst for the oxidation of low molecular weight compounds at low overpotentials and is less susceptible to poisoning by CO and other reaction intermediates. The use of such electrodes for the rapid determination of alcohol in beer and wine is described and the results show that the reproducibility and accuracy of this electrochemical method is comparable to traditional methods such as the near infrared methods used by the brewing industry.     

Electrochemical surface reactions of intermediates formed in the oxidative ethanol adsorption on porous Pt and PtRu

The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates were studied on electrodeposited Pt, Ru, Pt_0.92Ru_0.08 and Pt_0.85Ru_0.15 in 1 M HClO₄. A flow cell procedure was performed in order to separate surface reactions of intermediates formed in the oxidative ethanol adsorption from those reactions for ethanol in the bulk electrolyte solution. Oxidation and reduction reactions of adsorbed species were studied by potential-controlled electrodesorption spectrometry. No adsorbate formation was observed on a pure Ru electrode. In all cases, CO₂ was the sole product formed in the oxidative electrodesorption of the adsorbates. Using ¹²CH₃¹²CH₂OH and ¹²CH₃¹³CH₂OH, the oxidation reaction pathways of each C-atom to CO₂ were followed. On the other hand, methane and ethane were detected during the reductive electrodesorption of adlayer species. The onset potential for these reduction products shifts to more negative potentials as the Ru content of the alloy increases. The methane to ethane yield ratio decreases in the sequence Pt>Pt_0.92Ru_0.08>Pt_0.85Ru_0.15. A critical interpretation of the experimental data leads to a tentative yield of different adsorbed species as function of the Ru surface concentration.     

New effects in the electrochemistry of carbon dioxide on platinum by the application of potential perturbations

The electroformation and electrooxidation of carbon dioxide adsorbates were studied on polycrystalline and preferentially oriented platinum surfaces by the application of medium frequency potential perturbations in saturated carbon dioxide aqueous sulphuric acid solutions. Preferentially oriented platinum surfaces were obtained by the application of fast symmetric square wave potential programmes to polycrystalline electrodes based on well-known methodology. Two new electrochemical characteristics for the electrochemistry of carbon dioxide were observed after the application of the medium frequency routines, that is, an extended adsorption potential domain for the formation of carbon dioxide adsorbates, and novel voltammetric features for the two anodic stripping peaks. These effects upon carbon dioxide electrochemistry are dependent on the morphology of the platinum electrode surface and adsorption potentials.     

Flexible amperometric transducers for biosensors based on a screen printed three electrode system

Screen printed three electrode sensors comprising a platinum working, a carbon counter and an Ag ∣ AgCl pseudo reference electrode were developed employing polymer thick film inks. The sensors were constructed as amperometric transducers for multianalyte biosensors for use in batch, as well as in flow through systems. The characteristics of the sensors were determined. The active surface area of the Pt working electrodes was determined using electrochemical and SEM studies. Cyclic voltammograms of the ferricyanide/ferrocyanide couple showed that the reaction was quasi-reversible at these electrodes. Although the surface was not ideal for this redox couple, the sensors proved to be reproducible and well suited for the determination of hydrogen peroxide and thus for biosensors based on oxidases as biologically active compounds. The combination of two pretreatment steps, an additional heat curing and an electrochemical preconditioning step, was found to be most helpful to reduce background current and settling time of the sensors. Different aspects of the changing surface composition are discussed. The sensors with optimized preconditioning showed linear ranges from 10 μM up to at least 500 μM hydrogen peroxide and sensitivities of 6.97±0.20 nA μM^?1 hydrogen peroxide for uncovered, 4.01±0.08 nA μM^?1 hydrogen peroxide for PCS/BSA membrane covered and 0.222±0.002 nA μM^?1 hydrogen peroxide for Nafion^® coated platinum working electrodes. Moreover, optimized transducers with immobilized sarcosine oxidase (sensitivity: 2.30±0.07 nA μM^?1 sarcosine) demonstrated the feasibility of the sensor concept, the manufacturing and pretreatment processes for the development of enzyme sensors.     

Effect of adsorbed uracil and its derivatives on the rate of oxygen reduction on platinum in acid electrolytes

The rate of oxygen reduction in 0.5 M H₂SO₄ has been controlled by adsorbing uracil and its alkyl derivatives on a Pt electrode. Addition of an ethyl group to C(5), or methyl groups to the C(5) and C(6) positions of uracil, enhances the reaction rate. 5-Ethyluracil and 5,6-dimethyluracil have such an effect, however, only when their concentrations in the electrolyte are ≤0.1 mM. Substitution of the hydrogen on N(3) with CH₃, or exocyclic oxygens with OCH₃ groups results in the inhibition of the reaction; 1,3-dimethyluracil and 2,4-dimethoxypyrimidine (0.1 mM) are two systems that cause inhibition. Interaction between the surface Pt atoms and the N(3) and O sites on the organic molecule, especially in the presence of CH₃ or C₂H₅ groups on the C(5) and/or C(6) centers, are essential for the enhancement. Results of rotating disk electrode experiments suggest that at low overpotentials, 5-ethyluracil and 5,6-dimethyluracil increase the exchange current to produce higher reaction rates.     

Electrochemical behaviors of dimethyl ether on platinum single crystal electrodes. Part II: Pt(1 0 0)

The electrochemical behaviors of dimethyl ether (CH₃–O–CH₃, DME), which is a promising fuel for the fuel cell, on Pt(1 0 0) electrode in 0.5 M H₂SO₄ solution have been investigated in detail by electrochemical and in situ infrared (IR) measurements. As the potential is swept from 0.05 V (vs. RHE) to positive direction at 50 mV s⁻¹, the dehydrogenation peak of DME is observed around 0.33 V to generate a reaction intermediate and is further converted to carbon monoxide (CO) in more positive potential region. The main peak for DME bulk oxidation locates around 0.80 and 0.72 V in the positive- and negative-going potential sweep, respectively. The positions of these peaks strongly depend on the scan rate. The in situ IR observations show that (CH₃OCH₂–)_ad is an intermediate for the first dehydrogenation step of DME on Pt(1 0 0) surface and can serve as a precursor of the subsequent intermediate of adsorbed CO (CO_ad). Cyclic voltammograms of Pt high index single crystal planes Pt(hkl) show that the direct oxidation of DME is suppressed by decreasing the (1 0 0) terrace width. Based on these results, a possible reaction mechanism for DME electro-oxidation on the platinum single crystal electrode surface is proposed.     

Electrodeposition of Pt nanoparticles on undoped nanodiamond powder for methanol oxidation electrocatalysts

Undoped nanodiamond (ND) powder with average particle sizes of 5 and 100 nm were modified with platinum (Pt) nanoparticles by electrodeposition from 1.1 mM chloroplatinic acid solution. The structure and morphology of the composites were characterized by field emission-scanning electron microscopy and X-ray diffraction. The results showed that Pt nanoparticles were well-dispersed on the facet surfaces of ND particles. The electrooxidation of methanol on Pt-modified ND powders was investigated by cyclic voltammetry, which indicated its good electrocatalytic activity. Compared with 100 nm ND powder, the 5 nm ND powder modified with Pt nanoparticles exhibited better electrocatalytic activity.     

Oxidation of methylamine and ethylamine on Pt single crystal electrodes in acid medium

Cyclic voltammetry (CV) and Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) have been combined to analyse the oxidation of methylamine and ethylamine on platinum single crystal electrodes in an acidic medium. The oxidation of both amines on Pt(hkl) electrodes gives rise to the formation of adsorbed cyanide ad-layers, which have been detected by in situ infrared spectroscopy. In the case of Pt(111) the resulting adsorbed cyanide is rather stable but, on the contrary, the adsorbed CN-like species is highly reactive on Pt(100). It yields either adsorbed NO and CO₂ when the electrode is polarised above 0.7 V or adsorbed CO below 0.4 V. The detection of adsorbed cyanide is difficult to achieve at the Pt(110) surface. In the case of ethylamine, these adsorbed species are present in lower coverage than for methylamine. The substitution of one hydrogen atom by a methyl group in the methylamine makes the amine molecule more stable. So, the behaviour of ethylamine provides evidence for its lower electrochemical reactivity when compared with that of the methylamine molecule.     

国产紫杉醇及长春瑞宾联合铂类治疗晚期非小细胞肺癌的临床对照研究

目的　探讨国产紫杉醇及长春瑞宾加顺铂及卡铂联合方案对晚期非小细胞肺癌 (NSCLC)的疗效和毒副反应。方法　选取初治晚期NSCLC 181例 ,分别应用NP(长春瑞宾 +顺铂 )、TC(国产紫杉醇 +卡铂 )及TP(国产紫杉醇 +顺铂 )方案治疗。每例均完成两周期化疗后评价疗效及毒副反应。结果　三组患者近期有效率分别为NP组 42 .4%,TC组 40 .3 %,TP组 43 .3 %,三组间有效率比较均无显著性差异 ( χ2 =0 .10 86,P >0 .0 5 )。NP组中位生存期为 8.4个月 ,TC组 9.4个月 ,TP组 8.9个月 (P >0 .0 5 )。NP组 1、2、3年生存率分别为 3 9.0 %、16.9%、5 .1%;TC组分别为 41.9%、2 1.0 %、6.5 %;TP组分别为 40 .0 %、18.3 %、5 .0 %,三组间比较无统计学差异 ( χ2 =0 .14 0 4,P >0 .0 5 )。三组毒副反应均以骨髓抑制、脱发及恶心呕吐为主 ,但均未影响治疗。三组病例均无化疗相关死亡发生。结论　NP、TC及TP联合方案是治疗晚期NSCLC有效且耐受性较好的方案     

The intestinal parasite Pomphorhynchus laevis as a sensitive accumulation indicator for the platinum group metals Pt, Pd, and Rh

Concentrations of the platinum group elements Pt, Pd, and Rh were analyzed by adsorptive cathodic stripping voltammetry (Pt, Rh) and total-reflection X-ray fluorescence (Pd) in the intestinal helminth Pomphorhynchus laevis and its host Barbus barbus. The fish were caught in the Danube river south of the city of Budapest (Hungary) and were exposed to ground catalytic material for 28 days. Following exposure all three precious metals were taken up and accumulated in host organs and the parasites. Interestingly, in all tissues of the unexposed controls Pt was found, whereas Pd was not present in the muscle of the controls and Rh was not detectable in muscle and intestine of unexposed barbel. All metals were found at significantly higher concentrations in the acanthocephalan than in the tissues of barbel. These results are discussed with respect to the application of P. laevis as an accumulation indicator for metals.