摘要:

AbstractTwo electrodes modified with either nickel or cupric hexacyanoferrate films were evaluated and compared as sensors for nonelectroactive cations in a flow‐injection system. Both gave responses for group 1A and ammonium ions, but only the electrode modified with cupric hexacyanoferrate was sufficiently stable for use in flowing solutions. This electrode responded to K+, NH 4+, Rb+, and Cs+ions rather selectively. Within this group, the selectivity could be controlled from general to almost specific toward Cs+by the potential at which the electrode was poised. The electrode was compatible with a mobile phase of dilute nitric acid commonly used in ion chromatography, and chromatographic detection limits of 2 × 10−7M and linear responses over two decades were obtained. The electrode was applied to the ion chromatographic analysis of K+and NH 4+in urine and K+in blood serum

ISSN:1040-0397    

DOI:10.1002/elan.1140020402

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractFundamental harmonic ac voltammetry at flow‐by wall electrodes was found experimentally to be independent of the flow rate for rates from 0 to 2.1 L/min. Measurements were made with phase‐sensitive instrumentation. The ac peak current dependence on the concentration, the frequency and amplitude of the applied ac voltage, and the dc scan rate was the same in flowing or stationary solutions. The shape of the ac voltammogram was also not influenced by the flow rate. These results are general for experimental conditions that produce unrestricted diffusion and that maintain simple, reversible electron‐transfer mecha

ISSN:1040-0397    

DOI:10.1002/elan.1140020403

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe electrochemical characteristics of loprazolam mesilate have been evaluated in an aqueous solution using dc, ac, and normal and inverse pulse polarography, as well as cyclic voltammetry and controlled‐potential coulometry. This drug undergoes three different reduction steps. The first, a four‐electron transfer, corresponds to the reduction of the nitro group to give the corresponding hydroxylamine. The second, a two‐electron transfer, corresponds to the reduction of the azomethine group, either before or after (in an acidic solution) hydrolysis. The third wave corresponds to a four‐electron transfer in an acidic medium and to a two‐electron transfer in an alkaline medium. In an acidic solution, this third step involves the two‐electron reduction of the hydroxylamine group to the corresponding amine plus the two‐electron reduction of the double bond betweenN‐methylpiperazine and the imidazol group. In an alkaline solution, only the latter reduction takes place. Such behavior holds promise for analytical measureme

ISSN:1040-0397    

DOI:10.1002/elan.1140020404

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractHuman immunoglobulin G and A (IgG and IgA) were studied with square‐wave voltammetry. For IgG, three reduction peaks (HIGG1, HIGG2, and HIGG3) were observed under different conditions. HIGG1 and HIGG3 are strongly related to the pH of the buffer solution. In pH 7.5 phosphate buffer, the peak potential of HIGG2 is −0.58 V (vs. Ag/AgCl). A linear response holds for human IgG below 3.3 × 10−8M (5 ppm). As little as 1.1 × 10−10M (16 ppb) of human IgG is detectable after only 20 seconds of adsorptive accumulation in static solution.IgA has two flat adsorptive‐stripping responses (HIGA1 and HIGA2). The sensitivity of IgA is much poorer compared to IgG. HIGA2 at −0.44 V can be observed throughout the tested pH range with the maximum response between pH 6.0–6.2. In a static solution, a linear calibration graph can be obtained for 0.8–16.8 ppm IgA.IgG and IgA can be separated from each other by using HPLC with an AB × column. The response of 32 ppb IgG can be observed clearly. This research indicates the possibility of direct separation and detection of immunoglobulins from a real sample (e.g., human serum) by simply applying HPLC‐adsorptiv

ISSN:1040-0397    

DOI:10.1002/elan.1140020405

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe methods for the determination of nucleic acid bases by differential pulse cathodic stripping voltammetry in dimethyl sulfoxide are proposed and developed. One method uses mercury drop or film electrodes. The required anion is produced by the deprotonation of the parent molecule by added tetrabutyl‐ammonium hydroxide (TBAOH). Optimization of the method is discussed. The effects of deposition potential or time, scan rate, pulse height, TBAOH concentration, and other experimental parameters are examined. Included are the results of the determinations of thymine, uracil, cytosine, adenine, and guanine. The second method uses a mercury‐film rotating ring‐disk electrode. The anion, produced electrochemically at the disk held at a negative potential, is swept to the ring and deposited at a suitable, more positive potential. Detection limis for nucleic acid bases are 10−8t

ISSN:1040-0397    

DOI:10.1002/elan.1140020406

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA flow‐injection analysis (FIA) system utilizing a horseradish peroxidase‐modified amperometric electrode is described. The enzyme was immobilized through adsorption onto a glassy carbon electrode, and the system is used to determine hydrogen peroxide at submicromolar levels. The response is based on the enzymatic reduction of hydrogen peroxide in the presence of hydroquinone acting as an electron mediator. The oxidized quinone produced in the enzymatic reaction is reduced at the electrode, and the reduction current was found to be proportional to the concentration of hydrogen peroxide. Calibration curves were found to be linear between 2.5 × 10−8and 1.0 × 10−6M, and the method has a detection limit of 1.

ISSN:1040-0397    

DOI:10.1002/elan.1140020407

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThis work addresses the problem of signal resolution by partial least‐squares regression (PLS) for differential pulse stripping voltammograms. The performance of PLS is demonstrated for an example of calibration with mixtures of two analytes (Tl+and Pb2+) with strongly overlapping voltammograms. The accuracy of the determination of concentrations for validation mixtures was found to be considerably higher with PLS than with simple evaluation using currents observed at two potentials (requiring resolution of a system of two linear equations with two unknowns). Hence, PLS is recommended for computer‐assisted, on‐line voltammetric analysis of multicomponent sy

ISSN:1040-0397    

DOI:10.1002/elan.1140020408

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA new, simple procedure for the preparation of methyl methacrylate‐based bromide ion‐selective membrane electrodes with an internal solid contact is described. The stability, response range, and slope as well as the selectivity and interference‐free pH range of these electrodes were found to be satisfactory. The electrodes were applied to the determination of low bromine levels in biologically active substances with direct potentiometry and potentiometric titration after their combustion in an oxygen atmosphere. The results obtained are accurate and reprodu

ISSN:1040-0397    

DOI:10.1002/elan.1140020409

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of the adsorption of foreign organic compounds on the stripping voltammetry of metal adatoms deposited in submonolayer amounts at solid electrodes has been analyzed. It is shown that, for irreversible metal deposition processes, the adatom deposition current and, at a constant deposition time, the deposition charge are sensitive to the presence of the adsorbed foreign species on the electrode surface. Equations describing the dependence of the metal adatom deposition charge and the stripping peak current on the deposition potential, deposition time, concentration, and lateral exchange interactions between metal adatoms and adsorbed molecules have been derived. In the case of negligible exchange interactions, the peak current for adatom probe desorption decreases linearly with the surface coverage by foreign adsorbate. Direct evaluation of the kind and strength of exchange interactions is possible because the expression derived for the metal adatom desorption peak potential was used. It was found that the shift of the peak potential to more positive potentials is due to the lateral attraction exchange interactions, while the shift to more negative potentials was caused by the exchange repulsion interactions. No shift in the peak potential occurred in the absence of exchange interactions irrespective of the adatom surface coverage after the deposition step.

ISSN:1040-0397    

DOI:10.1002/elan.1140020410

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractCyclic voltammetry and chronocoulometry were used to study the electrochemistry of brucine. The oxidation of brucine 0.9 V versus a saturated calomel electrode at a carbon paste electrode produces a compound that undergoes reversible electrochemical behavior atEo′ = 0.47 V. The product formed on the oxidation of brucine undergoes a slow chemical reaction to produce a compound that shows reversible behavior atEo′ = 0.27 V. The hexadecane content of the carbon paste plays an important role in the observed behavior. Electrodes with low hexadecane did show oxidation of brucine, but irreversible waves occurred atEo′ = 0.47 and 0.27 V. These features were also displayed by a platinum electrode. Calcium oxalate incorporated into the carbon paste catalyzes the oxidation of brucine. Chronocoulometry was used to estimate the heterogenous rate constant for the oxidation of brucine at calcium oxalate‐modified and unmodified electrodes. The values found were 21.4 × 10−3cm/s for the modified electrode and 6.1 × 10−3cm/s for the unmodified electrode. Preliminary results on the use of brucine as a reagent for the determination of nitr

ISSN:1040-0397    

DOI:10.1002/elan.1140020411

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY