Oxand suisse proti stárnutí.
Transkript zde - Bestservis. Heyrovského AV ČR, oxand suisse proti stárnutí. Moderní Elektrochemické Metody Jetřichovice Za obsah veškerých textů oxand suisse proti stárnutí plnou zodpovědnost autoři.
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Bona fide vědečtí pracovníci si mohou pořídit jednotlivé kopie pro vlastní potřebu. Since then, many electroanalysts have continued in the studies with these electrodes, when focusing their attention on possible applicability in electrochemical stripping analysis.
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The number of papers concerning bismuth-based electrodes has proven their suitability and electrochemical properties similar to those of mercury-based electrodes with regard to the trace analysis of inorganic compounds.
As discussed below, our electroanalytical group has contributed to the field with respect to advantageous combination of the bismuth concept with carbon paste electrode material.
Key Words: Bismuth film, Bismuth-powder dispersion, Carbon paste electrode and microelectrode, Anodic stripping voltammetry. Introduction Electrochemical stripping analysis belongs to one of the key disciplines of scientific interest of the electroanalytical group at the University of Pardubice, Department of Analytical Chemistry.
It is now more than two decades, when the electrochemistry and electroanalysis with carbon paste electrodes, and related carbonaceous sensors had gained oxand suisse proti stárnutí main attention of Pardubice's electroanalysts 1. Such a research orientation was found proti stárnutí nadace tipy Estee be principal and, in fact, it lasts up until now, when gathering also development and testing of new detection systems; in particular, alternative to mercury electrodes whose popularity has declined rapidly in the recent years.
Today, bismuth-based electrodes are classified as a specific group of sensors having achieved the successful comeback from the beginning of the last century 2 into the contemporaneous electroanalysis. And bismuth is now generally adopted as a metal oxand suisse proti stárnutí electrochemical characteristics nearly comparable to those of mercury.
Up to now bismuth films have been electrolytically deposited mainly onto the various carbonaceous substrates — glassy carbon GCEcarbon paste CPEscreen printed carbon ink electrode SPEcarbon fibres and boron-doped diamond substrates BDDEbut also onto non-carbonaceous, metal compact substrates such as gold or platinum.
This contribution summarizes a part of Oxand suisse proti stárnutí group investigation which was focused on testing of bismuth films and bismuth powder dispersions in combination with carbonaceous electrode substrates 3, in particular carbon paste electrode CPEand comparison to some metallic electrodes by means of square-wave anodic stripping voltammetry SWASV of chosen inorganic oxand suisse proti stárnutí.
Survey of bismuth-based electrodes Bismuth films plated in situ, BiFs, which can be formed onto the several electrode substrates, are the most widely used bismuth-based configurations Originally, this type of electrodes has been extensively studied in combination with pyrolytic graphite or glassy carbon electrode substrates 6.
It was initially thought that bismuth film plated carbon paste electrodes 3 BiF-CPEs could not compete with other BiFEs when taking into account some analytical criteria or their applicability to real samples. However, the detection capabilities of first configurations of BiF-CPEs were typically worse and their practical application quite limited. The reason for such unsatisfactory results should apparently be attributed to the specific character of CPE surface that is highly hydrophobic and has a considerably irregular morphology.
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Thus one should expect that, if CPEs were to be employed electrode substrates for metallic films, they would require a very accurate optimization of the entire plating process. Regarding configurations prepared and operated in situ, one of the most crucial factors was attributed to the concentration of metal ions Bi to be plated and its ratio oxand suisse proti stárnutí the concentration of the target analyte s. This rule, originally postulated for MF-CPEs 7, we wanted to confirm also for BiF-CPEs by systematic study monitoring the influence of the bismuth concentration-to-metal ion concentration ratio on the sensitivity of heavy metal determination employing CPE.
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In this extensive work the effect of Bi III concentration over the wide concentration range of — M on the determination of the typical heavy metal couple of Cd II and Pb II ions, in the — M range was investigated by means of square wave anodic stripping voltammetry at in situ prepared BiF-CPEs 8. It was found out that the sensitivity of square-wave anodic stripping voltammetry generally depends on the Bi III -to-metal ion concentration oxand suisse proti stárnutí and that, unlike the usually recommended at least 10fold Hg II excess for in situ prepared mercury film electrodes MFEsBi III -to-metal ion ratios less than 10 are either optimal or equally effective at CPEs.
Surprisingly, even a Bi III to-metal ion ratio is enough to produce the highest Pb and Cd stripping peaks in all cases, whereas when this ratio exceeded value, a signal deterioration was obtained in most cases at the BiF-CPE electrodes. Similar study investigating the effect of bismuth-to-metal ion concentration ratio was accomplished by employing the carbon microdisc electrode CµE 9 as well as the new type of disposable electrode substrate based on carbon paste — carbon paste mini-electrodes CPmE Such electrodes combine the advantages of carbon paste its outstanding consistence together with its excellent conductivity and easily renewable surface with those of microelectrodes enhanced mass transfer rates due to non-planar diffusion together with small ohmic losses.
Because the ohmic potential drop, IR, is decreased as the measured currents are very low, electroanalysis in the presence of ambient or minimal electrolyte content is possible.
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This can be a very important factor in environmental analysis since the possibility to pollute the sample by addition of impurities incorporated in supporting electrolyte is absent.
Thus, our effort was further to test the effect of acetate buffer content in the sample solution, in the 0 to 0.
The results obtained have shown similar phenomenon as in the case of macroelectrode substrates, such is a fold excess of Bi III concentration to be equally effective to gain high sensitivity of the detection with possibility to use minimum or no buffer content.
Due to the systematic optimization of Bi III -to-metal ion concentration ratio very low detection limits for Pb II and Cd II were estimated using above mentioned carbonaceous electrode substrates see Tab. I overleaf. Bismuth powder carbon paste electrodes, Bi-CPEs, is a special sort of bismuth-based electrode which combines the advantageous properties of the carbon paste material with the favorable electrochemical properties of bismuth In principle, finely grounded metallic bismuth is mixed with the carbon paste during its preparation in a suitable quantum.
Table I Detection limits mol. The major advantage of this type of bismuth-based electrode is the possibility to employ them in analysis requiring slightly alkaline supporting media e.
An electrolyte of such a high alkalinity in combination with extremely negative deposition potential Normally, in the acetate buffer medium the stripping peak of copper is placed more positively than bismuth peak. Therefore it would not be correct to presume analysis on bismuth film electrode but rather the reaction between the electrode substrate and copper ions, because copper can also be fairly deposited onto the bare electrode. Bismuth-based electrodes have been primarily used for the trace analysis of heavy metals.
Nevertheless, some papers have shown their possible applicability also to the determination of selected organic compounds 17 or pharmaceutical preparatives References 1.
Vytřas K. Schwabe K.
Švancara I. Wang J.