摘要:

AbstractA personal view of the development of liquid chromatography/electrochemistry from a laboratory curiosity to a practical tool for routine use. An introduction to a special issue of the journal devoted to recent developments in this field.

ISSN:1040-0397    

DOI:10.1002/elan.1140040403

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe direct electrochemical detection of numerous polar aliphatic compounds is achieved at Au and Pt electrodes under the control of multistep potential‐time waveforms. In this technique, called “Pulsed Electrochemical Detection (PED),” the waveforms manage the sequential processes of sampling the faradaic signal, from the oxidation of analyte, followed by oxidative cleaning and reductive reactivation of the electrode surfaces. The response mechanisms in PED are strongly influenced by surface properties of the electrodes and, therefore, members of each chemical classification detected are observed to produce virtually identical voltammetric response. Consequently, applications of PED have their greatest analytical significance when coupled with Liquid Chromatography (LC) to achieve a priori resolution of complex mixtures. The basic concepts of PED are reviewed and LC‐PED results are presented for a variety of samples containing mixtures of alcohols, carbohydrates, alkanolamines, amines, and sulfur co

ISSN:1040-0397    

DOI:10.1002/elan.1140040404

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractIn previous studies we have developed a method for the electrochemical detection of aromatic amino acids, sulfur‐containing amino acids, peptides, and proteins in HPLC by using photolytic derivatization approaches. Upon irradiation, nonelectroactive (or even inherently electroactive) amino acids and peptides can be converted to electroactive (or more electroactive) compounds, in an on‐line, postcolumn manner, which can be detected electrochemically in HPLC. In the case of proteins, the same method can be used to change the electroactivity of proteins photochemically. It is important to identify these photochemically converted compounds, especially those which are electroactive, in order to understand the detection mechanisms of the method. In this paper the results of identification of electroactive photoproducts for aromatic amino acids, peptides, and proteins are presented. Mainly, these studies were carried out by HPLC and direct electrochemical detection of off‐line photolyzed ana

ISSN:1040-0397    

DOI:10.1002/elan.1140040405

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractConstant potential amperometric detection of underivatized polypeptides and proteins can be carried out at metallic copper electrodes. When coupled with liquid chromatography, this approach provides a sensitive and selective method of analysis for these compounds. Two different detection mechanisms can be employed: a neutral pH, low potential oxidation process attributed to enhanced dissolution of the electrode by peptide species capable of forming soluble Cu(II) complexes and a high pH, high potential electrocatalytic oxidation of the analytes. Of the two approaches, the latter process was found to be more attractive for LCEC applications as it was useful for a wider range of peptides and proteins and gave substantially larger currents and lower detection limits. The compounds exhibiting useful electrocatalytic response at the copper electrode ranged from oligopeptides such as enkephalins and bradykinin to very large proteins such as glucose oxidase (F.W. 160,000) and catalase (F.W. 240,000). The response was not dependent on the presence of tyrosine, tryptophan, or cysteine amino acid units and was shown to be compatible with both ion‐exchange and reverse‐phase separation sche

ISSN:1040-0397    

DOI:10.1002/elan.1140040406

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe first part of the paper provides a review of the pre‐ and postcolumn derivatization systems used in Column Liquid Chromatography (CLC) in combination with immobilized enzyme reactors (IMERs) and electrochemical detection (EC). In the second part, an outline of important factors to consider in the optimization of CLC‐IMER‐EC systems are presented. Three industrial applications are described utilizing enzyme‐based detection or enzymes for sample handling purposes. In two of the cases, CLC‐IMER were used in combination with amperometric detection using chemically modified electrodes (CME). These applications were performed in our laboratory, and the high selectivity and sensitivity of these systems as well as the problems encountered in these complex samples will be

ISSN:1040-0397    

DOI:10.1002/elan.1140040407

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractVoltammetric detection is a potentially powerful method of detection for high performance liquid chromatography and flow injection analysis. A problem that needs a solution is its inferior detection limit compared to that obtained with amperometric detection. The shape of the potential waveform has been investigated in the search for methods of improving the detection limit of voltammetric detection. As a result, large amplitude sine wave potential perturbations have been found to give improved signal‐to‐noise ratios when compared to the values found for a corresponding triangle waveform (by a factor of from 1.1 to 5). This is principally due to the fact that the background current from a large amplitude triangle perturbation is spread over a wider frequency region. Signal processing techniques such as digital filtering have also been investigated. Digital bandpass filtering can be used to improve the signal to noise ratio by a factor of 2–13. Qualitative information (e.g., half‐wave potential) is obtained through observing the phase angle at harmonics of the fundamental fr

ISSN:1040-0397    

DOI:10.1002/elan.1140040408

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA method for photoelectrochemical detection of alcohols in liquid chromatography and flow injection analysis based on the reaction of the analyte with a photosensitized quinone (benzoquinone) has been developed. Irradiation of the flowing solution and electrochemical detection of the generated photoproduct is carried out within the detector flow cell. Pulsed amperometric detection produced higher sensitivities than conventional potentiostatic amperometry. Samples of vodka and beer were successfully analyzed using the proposed method.

ISSN:1040-0397    

DOI:10.1002/elan.1140040409

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractAn amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible electric conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large‐are working electrodes; typical limits of detection amount to analyte concentrations between 10−7and 10−6mol/dm3, corresponding to subnanogram amounts in common HPLC sample volumes. The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal‐phase HPLC or to methods with programmed composition of the mobile phase (gradient e

ISSN:1040-0397    

DOI:10.1002/elan.1140040410

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractAn ion chromatographic method for the separation and determination of As(III) empolying both constant and pulsed potential amperometric detection at platinum electrodes has been compared using cylindrical wire, thin layer, and wall‐jet flow cell detectors. Operational parameters such as limit of detection, linear dynamic range, stability, reproducibility, and flow rate dependence are reported for each detector cell. The different detector designs have features which make them individually appealing, depending on the type of application being considered and which operational parameter is most important. However, the limit of detection with the wall‐jet electrode of 1 × 10−9M is superior to the other electrode designs (this may not necessarily be the case for other analytes) and makes this the preferred method for the determination of arsenic in bottled mineral water. Additionally, a lower limit of detection is achieved with constant potential amperometric detection than is the case with pulsed potential amperometric detection, which suggests that pulsed methods may not be advantageous for the detection of species at potentials where a large background current is exhibited at very positive potentials as required for the determination of a

ISSN:1040-0397    

DOI:10.1002/elan.1140040411

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractElectrochemical detection has been shown to be a sensitive method of detection in capillary electrophoresis (CE). The small sample volume required for CE makes it ideal for the analysis of microdialysis samples. In this paper, capillary electrophoresis with electrochemical detection is utilized in the analysis of samples obtained during continuous monitoring of the pharmacokinetics of L‐dopa in the rat. The detection limit for L‐dopa was 98 attomoles or 3.9 ng/mL. The elimination half‐life was calculated to be 10.3 ± 1.1 minutes. Voltammetric characterization was used to verify the identity of L‐dopa and its metabolites. The effects of electrochemical pretreatment on the detector performance was also inve

ISSN:1040-0397    

DOI:10.1002/elan.1140040412

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY