ISSN:1040-0397    

DOI:10.1002/elan.1140090102

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe current status of describing the selectivity of liquid membrane ion‐selective electrodes (ISEs) is reviewed. For ISEs that show Nernstian response toward all measured ions, the mixed ion response can often be described rigorously by a newly developed model that establishes required Nikolskii coefficients for a given target application. For ions of different charge, these obtained values are significantly different than predicted using the traditional Nikolskii–Eisenman equation. In contrast, for ISEs that show non‐Nernstian responses toward highly discriminated ions, two different procedures are recommended, depending on the scope of the experiment. Selectivities obtained with the so‐called matched potential method yield information about the apparent selectivity behavior of ISEs in real‐world samples, irrespective of theoretical expectations, but can, for the very same reason, generally not be used to predict the empirical selectivity for different analytical situations. On the other hand, experimental procedures are presented that allow for the determination of fundamental Nikolskii coefficients of such membranes, i.e., Nernstian slopes can now often be obtained by carefully adjusting the experimental conditions. Such values more closely reflect the ion extraction behavior of the membrane and can be used for characterization and optimization purposes. Each of the procedures has its validity and the respective values should preferably be reported simul

ISSN:1040-0397    

DOI:10.1002/elan.1140090103

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

ISSN:1040-0397    

DOI:10.1002/elan.1140090104

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAntimony, in both its trivalent and pentavalent states may be detrimental to the electrochemical deposition of zinc. Ideally, therefore antimony should be monitored in both oxidation states throughout an electrolytic zinc plant. At hydrochloric acid concentrations (>4 M) both antimony(III) and (V) present in zinc plant electrolyte can be reduced at a hanging mercury drop electrode (HMDE) to form an antimony amalgam, Sb(Hg). Consequently a very sensitive analytical signal is obtained for the determination of total antimony by differential pulse anodic stripping voltammetry (DPASV) using a 1:1 mixture of plant electrolyte and concentrated hydrochloric acid. In contrast, at low acid concentrations (0.1 M) predominantly only antimony(III) can be reduced and therefore determined in zinc plant electrolyte by DPASV at a HMDE by use of a 1:1 mixture of plant electrolyte and 0.2 M hydrochloric acid. The antimony(V) concentration is calculated by the method of subtraction of antimony(III) from total antimony. Consequently, simple addition of high and low concentrations of hydrochloric acid to zinc plant electrolyte can be used to provide a suitable electrolyte for both off‐line and on‐line methods for determining the concentration of total antimony, antimony(III) and antimony(V). The method described in this article has been applied to a wide range of zinc electrolyte samples and an on‐stream analyzer technique has been successfully used for several years at the Pasminco Metals‐BHAS electrolytic zinc plant in Port Pirrie, Au

ISSN:1040-0397    

DOI:10.1002/elan.1140090105

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe fast electrochemical deposition of both mercury and amalgam films, a crucial step in analytical anodic stripping voltammetry, is demonstrated to occur in the presence of power ultrasound emitted from an immersion horn probe which was placed opposite the working electrode in a conventional three electrode cell. Due to considerably enhanced mass transport the rate of deposition is strongly increased compared to ‘silent’ conditions. The total amount of mercury adhering to a glassy carbon electrode surface, however, is limited to a ‘thin film’ of microscopically small droplets of mercury as shown by atomic force microscopy and voltammetry. Due to surface forces induced by ultrasound, abrasion of some of the deposit occurs and after a certain period of time the parallel electro‐deposition and abrasion processes reach a ‘steady state’.The deposition of mercury in the presence of Pb2+or Cu2+results in the formation of an amalgam and well‐defined, very sharp ‘stripping’ responses for the oxidation process of the corresponding amalgam were detected. The merit of insonation in analytical electrode preconcentration tec

ISSN:1040-0397    

DOI:10.1002/elan.1140090106

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA complex of colloidal gold (Au) particles and D‐fructose dehydrogenase was prepared. A glassy carbon (GC) electrode was modified with the complex. The anodic current response to D‐fructose was measured by using the GC electrode modified with the complex at +0.5 V (vs. Ag/AgCl). Response time was within 15 s. No current response was observed in the absence of enzyme, so that the increased oxidation current was confirmed to be caused by the electron transfer from enzyme to electrode. Linear response range of the electrode was up to 0.5 mM fructose concentration. Fructose concentrations of soft drinks which were determined using the electrode agreed well with the results of the F

ISSN:1040-0397    

DOI:10.1002/elan.1140090107

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA method employing computerized potentiometric stripping analysis has been developed in order to determine trace levels of thallium in various environmental samples. The method is based on the preconcentration of T1 onto a mercury film electrode (formed in situ) with a subsequent reoxidation of amalgamated T1. A deaeration of the solution as well as the use of EDTA have resulted in a significant improvement of the sensitivity. In a supporting electrolyte containing 0.02–0.07 M HNO3+ 0.02 M CH3COONa + 0.001 M EDTA + 6 × 10−5M HgCl2, the analytical signal versus concentration dependence is linear from 9 × 10−11to 2.5 × 10−8M T1 (preconcentration time from 5 to 30 min). A detection limit of about 5 × 10−11M T1 (0.01 μg/L) is achieved when using preconcentration for 30 min. Despite a relatively high acidity of the supporting electrolyte used (pH 1.0–2.5), EDTA is capable to suppress the interferences from PbIIions up to a 500‐fold excess in concentration and from CdIIand CuIIup to their 100‐fold excess, respectively. Nitric acid has been incorporated into the supporting electrolyte as its constituent in order to determine T1 directly in the samples decomposed by means of high pressure ashing. The applicability of the method is demonstrated on various samples such as tap water (spiked), rain water, river sediment or sewage sludge. The results agree well with those obtained by isotope dilution‐mass spectrometry. The method has also been tested to determine T1 in digested biological samples (e.g., pine needles, poplar leav

ISSN:1040-0397    

DOI:10.1002/elan.1140090108

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractFlow characteristics of a versatile large‐volume flow‐through electrochemical cell, which features exchangeable disk, ring‐disk or microdisk working electrodes, are presented. The cell operates in a radial‐flow thin‐layer, wall‐jet or wall‐tube mode, under amperometric or voltammetric conditions, being therefore suitable for flow analytical techniques, such as high performance liquid chromatography (HPLC) and flow injection analysis (FIA). The operation mode is selected by using the inlet capillary either of a flat or conical nozzle and by suitably adjusting the nozzle‐to‐electrode distance. The cell is equipped with a micrometer screw which allows for adjusting of this distance to be as small as 10 ± 5 μm. The inlet solution stream is centered axially against the working electrode surface. Under radial‐flow thin‐layer conditions, flow‐through detection at a ring‐disk electrode benefits from shielding and collecting properties which are enhanced as compared to those for the rotating ring‐disk electrode conditions. The HPLC extracolumn effects due to detection were determined by the peak variance analysis of a mixture of regio isomers of nitrobenzene derivatives. Despite the large (35mL) geometric cell volume, the effective detection volume of the cell is of the microliter order. Therefore, the cell is suitable for detection both in the analytical and microbore‐column HPLC. Due to the large geometric cell volume, solution composition can be different, under wall‐jet conditions, for detection than that for HPLC separation. Hence,in situpostcolumn modification of the mo

ISSN:1040-0397    

DOI:10.1002/elan.1140090109

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe mass transport dynamics of ferrocene in polyelectrolyte polyethylene glycol lithium perchlorate (PEG · LiClO4) was studied by using chronoamperometry at a microdisk electrode. Chronoamperometry is a powerful method for the study of mass transport in polyelectrolyte, it has many advantages over the conventional methods at a microelectrode and the steady‐state method at an ultramicroelectrode. By using this method the apparent diffusion coefficientDappand concentrationCaof the electroactive species, can be estimated from a single experiment without previous knowledge of either one. We have estimatedDappandCaof ferrocene in PEG · LiClO4polyelectrolyte from 25°C to 75°C. The dependence on the concentration of electroactive species was observed. The diffusion coefficients decrease with increasing ferrocene concentration and decreasing temperature. The mass transport mechanism is explained by using a free volume

ISSN:1040-0397    

DOI:10.1002/elan.1140090110

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY

摘要:

AbstractA carbon paste electrode modified with 1‐(2‐pyridylazo)‐2‐naphthol was fabricated and used to preferentially accumulate Mn(II) at open circuit. After medium exchange, the accumulated Mn(II) at the electrode surface was electrochemically oxidized. The hydrated MnO2thus formed was then cathodically stripped using differential pulse voltammetry. Various factors influencing the accumulation and stripping were studied. An optimized procedure was then developed for the determination of Mn(II). Mn(VII) could also be determined by chemical conversion to Mn(II) using acidified H2O2. Following this, the Mn(VII) concentration could be obtained by subtraction. Under optimum conditions, a detection limit of 6.9 × 10−9M Mn(II) (0.38 ppb) was found for 200s accumulation. For 8 determinations, each of Mn(II) concentrations of 1.00 × 10−6M, 1.00 × 10−7M and 1.00 × 10−8M, relative standard deviations of 2.90%, 4.46% and 7.20% were obtained, respectively. Selected metal ions were tested for interferences and it was found that, when determining 1.00 × 10−6M Mn(II) (150s accumulation), Co(II), Hg(II) and Fe(II) at 1.00 × 10−5M interfered. These interferences were readily eliminated by masking with complexing agents such as sodium citrate and sodium diethyldithiocarbamate. The developed method was tested using a certified sample and then applied to the determination

ISSN:1040-0397    

DOI:10.1002/elan.1140090111

出版商:VCH Verlagsgesellschaft mbH    

年代:1997

数据来源: WILEY