摘要:

AbstractBright, freshly‐polished Ti electrodes give minimal cathodic response for O2and H2O2in 1.0 M NaOH. However, the response is increased gradually by repeated application of a triangular waveform within the approximate potential limits of O2response (ca. −1.5 to −0.7 V vs. SCE). This same voltammetric pretreatment applied for excessive periods results in formation of golden films on the Ti surfaces that are active for reduction of O2and H2O2. Levich plots of cathodic current for O2and H2O2at rotated golden‐Ti disk electrodes in 1.0 M NaOH (−1.35 V) are linear over a large range of rotational velocity (42 to 513 rad s−1), a behavior considered to be indicative of fast heterogeneous kinetics. Ring‐disk data demonstrate that a small amount of H2O2is produced throughout the potential region for O2reduction and H2O2is concluded to be an intermediate product in the O2‐reduction mechanism. These observations are consistent with those reported previously for single‐cryst

ISSN:1040-0397    

DOI:10.1002/elan.1140090402

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe chemical oxygen demand (COD) of solutions containing various organic compounds is calculated from the net faradaic charge (Qnet) estimated for the total electrolytic oxidation of CrIIIgenerated during oxidative degradation of the organic compounds in acidic media containing excess CrVI. Values ofQnetfor conversion of CrIIIto CrVIare estimated from the linearized chronoamperometric data plotted as In {itat, t} vs.t. This procedure is preferred over determinations ofQnetfrom the total integrals ofitotover the entire electrolysis period because of large errors that can result from uncertainty in the background current (ibkg) fort→ ∞. The proposed coulometric procedure offers the benefit that reagent solutions can be reused, thereby minimizing the need for disposal of wastes containing toxic CrVI. This procedure was applied in a single digest solution for consecutive determinations ofCOD. AverageCODvalues for potassium acid phthalate and glucose were 103.8% (s‐ 6.0,N‐ 10) and 100.2% (s‐ 4.2,N‐ 11), respectively, based on the theoretical degradation to CO2. In comparison for these same samples, an EPA approved method, based on colorimetric determination of CrIII, gaveCODvalues of 101.4% (S‐ 1.4,N‐ 5) and 100.1% (s‐ 1.4,N‐ 5) of the theoretical. Statistical tests indicate no significant difference in theCODvalues determined for these compounds using the coulomet

ISSN:1040-0397    

DOI:10.1002/elan.1140090403

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe use of the channel flow cell for ultraviolet‐visible (UV‐vis) spectroelectrochemical experiments has been developed to determine the diffusion coefficients of electrogenerated species by means of monitoring the transient absorbance response resulting from a potential step at a working electrode immediately upstream of the incident spectrophotometric beam. The technique is applied to measure the diffusion coefficient oftris(4‐bromophenyl)amine (TBPA) radical cation in acetonitrile at 25°C. It is shown that the diffusion coefficient of electrogenerated TBPA radical cation (1.64 ± 0.02 × 10−5cm2s−1) is very close to that of the parent molecule (1.57 ± 0.03

ISSN:1040-0397    

DOI:10.1002/elan.1140090404

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA bienzyme electrode for monitoring biologically important peptides containing tyrosine has been established on the basis of mushroom tyrosinase and quinoprotein glucose dehydrogenase (GDH). Tyrosine residues bound in the peptide chain are oxidized by tyrosinase resulting in consumption of oxygen. Subsequently, the dopaquinone residues are reduced in the GDH catalysed reaction which is driven by an excess of glucose. This reaction cycle leads to a considerable increase of sensitivity. Both enzymes were entraped in poly(vinyl)alcohol matrix and placed on the surface of a Clark‐type oxygen electrode (the working platinum electrode was potentiostated at −600 mV) (vs. Ag/AgCl reference electrode) between a polypropylene and cellulose membrane. The bienzyme‐modified Clark‐type oxygen electrode has a lower detection limit of 0.2 μM for the opioid peptides Tyr‐D‐Ser‐Gly‐Phe‐Leu‐Thr, Leu‐enkephalin, Tyr‐D‐Ala‐Gly‐Phe‐D‐Leu and morphiceptin. The dependence of response of the electrode on the length of peptide chain and position of tyrosine residue is discussed. The new electrode has been applied to the quality control of tyrosine containing peptides from pharmaceutical formu

ISSN:1040-0397    

DOI:10.1002/elan.1140090405

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn improved version of the disposable multichannel immunochemical biosensor for the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) based on a screen‐printed amperometric transducer and monoclonal antibodies (MAb) against 2,4‐D is reported. Entrapment within a thin Nafion film was used for the direct immobilization of MAb at the electrode surface. The amount of the tracer (2,4‐D conjugated to acetylcholinesterase) bound in a competitive immunochemical reaction was determined amperometrically using acetylthiocholine iodide as substrate. The measuring procedure (times of incubation with tracer and substrate, pH, tracer concentration) was optimized. The sensor was able to detect less than 0.01 μg/L of free 2,4‐D in water. One analysis (8 samples) was completed in 30 min (20 min for immunochemical reaction, 5 min incubation with substrate, 5 min measurement). The performance of the immunosensor (two configurations) was evaluated on real samples (tap water) with added 2,4‐D. The determined amounts (mean values 0.097 to 0.105 and 0.89 to 1.13) corresponded well with the added contents of 2,4‐D (0.100 and 1.00 μg

ISSN:1040-0397    

DOI:10.1002/elan.1140090406

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe performance of metallized carbon oxidase‐based biosensors is critically compared with that of mediator‐based enzyme electrodes. Dimethyl ferrocene and rhodium metal centers are used as model mediator and catalyst, respectively, in connection to carbon‐paste electrode transducers and assays of glucose. The rhodium‐containing bioelectrode displays enhanced selectivity (particularly improved discrimination against ascorbic acid), lower sensitivity, faster response time, greater oxygen dependence, and similar detection limit in comparison to the mediated electrode. In addition to assessing the relative merits of both strategies, the data offer useful insights into the behavior of these ‘first’‐ and ‘second‐generation’ oxidase ampe

ISSN:1040-0397    

DOI:10.1002/elan.1140090407

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA poly(4‐vinylpyridine)/mercury film electrode (PVP/MFE) was used for the determination of trace thallium(III) by square‐wave anodic stripping voltammetry (SWASV). Thallium(III) is preconcentrated onto the PVP/MFE as the anionic forms in chloride medium by the ion‐exchange effect of the PVP. The high solubility of thallium in mercury further facilitates the accumulation effect. Various factors influencing the determination of thallium(III) were thoroughly investigated. This modified electrode displayed good resistance to interferences from surface‐active compounds and common ions and increased sensitivity when used in conjunction with SWASV. In addition, detection can be achieved without deoxygenation and the electrode can be easily renewed. Applicability to various water samples is illu

ISSN:1040-0397    

DOI:10.1002/elan.1140090408

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA novel microelectrode assembly containing more than 1000 carbon microdisks has been used to study the interfacial electron transfer kinetics of cytochrome c and several other redox proteins. It is demonstrated that near‐steady‐state current–voltage curves can be obtained without solution stirring, and without significant mains interference or capacitive charging currents. In addition, it is demonstrated that concentrations of redox proteins as low as 1 μM can be detected in solution. Finally, it is shown that the surfaces of carbon microdisk assemblies can be successfully coated with thin films of poly(ester sulfonic acid), which allows reactants to be studied in a membrane‐like env

ISSN:1040-0397    

DOI:10.1002/elan.1140090409

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo calix[4]arene derivatives, in the partial cone conformation, with sulfur‐containing functionalities, were tested as neutral carrier ionophores in potentiometric silver‐selective electrodes of conventional membrane and membrane‐coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2‐nitrophenyl octyl ether orbis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p‐chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec−1) in the range 10−4–10−1M and excellent selectivity [logKAg,MH+<−1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in th

ISSN:1040-0397    

DOI:10.1002/elan.1140090410

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAn NH 4+‐ISFET sensor based on PVC membrane technology with improved long‐term stability has been developed. As a new approach, the plasticizer (tetra‐n‐undecyl) 3,3′,4,4′ ‐benzhydroltetracarboxylate (ETH2112) was used in membrane preparation. Its lipophilic nature provides a restricted diffusion of the membrane components to the external solution and improves membrane adhesion to the gate area of the ISFET. The good performance of this plasticizer was confirmed by comparison with usual plasticizers applied in standard ISE technology. Moreover, the durability and stability of the sensor were enhanced by the application of a graphite‐epoxy layer as an internal reference between the gate area and the PVC membrane. This composite layer permits the reduction of the optical sensitivity and improves the adherence of the PVC membrane to the ISFET surface. Furthermore, this composite layer acts as a plug, preventing the entrance of water upon the encapsulant‐chip interface, thus protecting electrical connections from moisture. As a result, an NH 4+‐ISFET with a long‐term stability of three months and a sensitivity of −58.7 ± 2.3 mV decade−1in a linear range of 10−5−0.1 mol dm−3has been developed. The application of this sensor to a continuous‐flow system has confirmed the feasibility

ISSN:1040-0397    

DOI:10.1002/elan.1140090411

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY