Height Of Mercury Column Research Articles

Capacitive measurement of mercury column heights in capillaries

The detection of changes in volume, e.g., in expansivity or aging measurements, are often translated into mercury column height within a glass capillary. We propose a capacitive technique for measuring the meniscus position using a cylindrical capacitor with mercury as the inner electrode, the capillary material as the dielectric, and a metal coat covering the outside surface of the capillary as the second electrode. The measured capacitance changes linearly with meniscus height, as long as the top mercury level remains within the range of the outer electrode. With the demonstrated noise level of 48 nm for our preliminary setup, meniscus height changes beyond 100 nm can be observed via the capacitance.

Catalytic brdicka-type systems in alternating-current square-wave voltammetry

Conventional kinetic and adsorption parameters of signals detected by alternating-current squarewave voltammetry in the catalytic systems cobalt(II)-NH3-cysteine (cystine) and nickel(II)-NH3-cysteine (cystine) in the presence of excess catalyst (metal ions) were discussed. The parameters for the optimization of the detected signals (mercury column height and mercury dropping rate) were considered. The characteristics of the cobalt(II)-NH3-cystine-containing protein indicator system were qualitatively compared with those of the model cobalt(H)-NH3-cystine system.

Conventional kinetic characteristics of signals in alternating-current square-wave voltammetry

Kinetic parameters typical of alternating-current square-wave voltammetry were considered. In the absence of precise time characteristics of instruments, we proposed to use the following conventional characteristics obtained from experimental data: instrument constant (H); kinetic parameter of irreversible electrode processes (Φ); and kinetic parameter of catalytic processes (Ψ). Particular attention was given to the effect of mercury column height on the kinetic characteristics

Improved measurement accuracy and uncertainty budget of the BIPM primary standard manobarometer

The uncertainty budget of the BIPM primary standard manobarometer of the BIPM-Jaeger type, which has been replicated commercially for use in other national metrology laboratories, has been re-assessed. The effect of different media on the paths of the two white-light beams sensing the mercury column height has been studied using the actual spectrum of the light. The dominating contributions to the overall uncertainty have been reduced substantially.

Catalytic polarographic waves of cobalt(II) in the presence of sodium sulfide (SH− form) in borax – ammonium chloride

The presence of SH− ions in a medium containing ammonia (borax–NH4Cl) and cobalt(II) gives rise to a catalytic cobalt(II) prewave and a catalytic hydrogen wave, both of which manifest more positive potentials than the cobalt(II) reduction wave. The effects of time, sulfide and cobalt concentrations, mercury column height, and gelatine and neutral salts addition are discussed. In addition, the characteristics of the current–time and electrocapillary curves are shown. The results obtained suggest a mechanism whereby a cobalt(II) prewave is produced by a cobalt(II) complex with SH− in the 1:2 relationship. Hydrogen catalytic evolution is attributed to the reduction of a protonated complex.

Molybdenum Catalysed Polarographic Reduction of Iodate

Abstract Polarographic catalytic reduction of iodate by molybdenum (VI) is investigated in an acetate-acetic acid solution of pH 5. The catalytic wave consisted of a peak at around -1.6 V vs SCE. The effect of pH, metal ion concentration, oxidant concentration, mercury column height, surfactants and neutral salt on the wave characteristics is studied. Probable explanations are offered.

Catalytic hydrogen wave in presence of dimethydithiocarbamate and cobalt(II)

The presence of dimethyldithiocarbamate (Me 2DTC) in a medium containing ammonia (borax-NH 4Cl and NH 4OH-NH 4Cl buffer) and cobalt(II) gives rise to a catalytic hydrogen wave. The effects of Me 2DTC and cobalt(II) concentrations, mercury column height and addition of gelatin on the catalytic hydrogen wave are discussed. A mechanism for this wave is proposed in which the H 3O + is reduced on Co(0) stabilized by the Me 2DTC at the mercury surface.

Structural effects on the polarographic behavior of some barbituric acid derivatives

Eight pharmaceutically important 5,5′-disubstituted barbituric acid derivatives were studied by differential pulse polarography (DPP). Borate buffer (0.05 M at pH 9.30) was selected as the best supporting electrolyte for the determination of the substances by DPP. The effects of parameters such as pH, temperature, mercury column height and concentration on peak potential and peak height were also studied to elucidate the electrode processes and to examine the structural relationship between the derivatives. From the effects of the above-mentioned parameters and from the αn values it was concluded that the reaction mechanisms were the same for all the derivatives and the linear free energy relationship (LFER) could be applied. The relationship between polarographic behavior and pharmacological activity was also investigated.

Structural effects on the polarographic behavior of some barbituric acid derivatives

Eight pharmaceutically important 5,5′-disubstituted barbituric acid derivatives were studied by differential pulse polarography (DPP). Borate buffer (0.05 M at pH 9.30) was selected as the best supporting electrolyte for the determination of the substances by DPP. The effects of parameters such as pH, temperature, mercury column height and concentration on peak potential and peak height were also studied to elucidate the electrode processes and to examine the structural relationship between the derivatives. From the effects of the above-mentioned parameters and from the αn values it was concluded that the reaction mechanisms were the same for all the derivatives and the linear free energy relationship (LFER) could be applied. The relationship between polarographic behavior and pharmacological activity was also investigated.

Catalytic pre-wave of nickel(II) in presence of cocarboxylase (disulfide form) in borate medium

A brief study is made of the nickel(II) polarography in borate medium. The nickel(II) in borate medium gives one or two waves depending on its concentration as well as the medium composition. In a borate medium, cocarboxylase in its disulfide form gives a nickel(II) pre-wave. The effects of the cocarboxylase (disulfide form) concentration, nickel(II) concentration and mercury column height on the pre-wave are described. The effect of neutral salts on the pre-wave is studied and it is seen that an increase in the ionic strength is accompanied by a decrease in pre-wave current, being of decreasing effect in the order K + < Na + < Li +. The electrocapillary curves are present, and it is shown that the presence of cocarboxylase (disulfide form) in the solution causes a decrease in the interfacial tension. The results are discussed and a mechanism for the electrode process of the pre-wave is proposed. Using the approximate method for the catalytic currents, nickel(II) and cocarboxylase-thiol are shown to form the catalytic complex in the relationship 1:1.

The Polarography of the Cadmium(II)–2-Carboxy-1-pyrrolidinecarbodithioate Chelate

Abstract The electrochemical behavior of the cadmium(II) ion in the presence of 2-carboxy-1-pyrrolidinecarbodithioic acid (H2cpcd) as a chelating agent was investigated in an alkaline medium by d.c. polarography, a.c. polarography, cyclic voltammetry, and chronopotentiometry. The cadmium(II) chelate gave a reversible two-electron reduction wave at −0.86 V vs. SCE, with a postwave at −0.95 V. From the dependence of the total wave height on the mercury column height and from the methods of cyclic voltammetry, the electrode reduction of the cadmium(II) chelate was found to be diffusion-controlled. The diffusion current constant was 2.42 μA mol−1 m3 mg−2⁄3 s1⁄2. The postwave was identified as an adsorption wave of the cadmium(II) chelate from the dependence of the postwave height on the mercury column height, the a.c. peak height, the electrocapillary curves, and the results of chronopotentiometry. The surface excess of cadmium(II) chelate adsorbed on the mercury electrode was evaluated by means of three different electrochemical techniques. The composition of the cadmium(II)–cpcd chelate in the presence of excess H2cpcd was Cd(cpcd)22−, and the overall stability constant was estimated to be 8.0×1012 at 25.0 °C and μ=1.5.

A polarographic study of the pre-sodium type catalytic hydrogen wave exhibited by selenocystine

Selenocysteine, formed by reduction of selenocystine at the DME at about −0.6 V in an ammoniacal buffer, produces a pre-sodium catalytic hydrogen wave. The effects on this wave of variation of several physico-chemical parameters such as selenocystine concentration, mercury column height, buffer capacity and concentration, and ionic strength, have been studied. The results obtained all support the conclusion that the wave is of pre-sodium type. The partially protonated species of selenocysteine seem to be catalytically active. An analytical determination of selenocystine in the presence of selenocysteine, based on this study, is proposed.

Reversible electrode reactions: Reduction of Cd-oxalate-succinate complex at D.M.E.

The reduction of Cd-oxalate-succinate system has been studied at D.M.E. It has been found to be reversible and diffusion-controlled involving two electrons as indicated by slope of straight line curve of E de vs. log ( i i d − i ) and direct proportionality of diffusion current to the effective height of mercury column. The stability constants β 12 β 11 and β 21 for complexes Cd(ox.)(succ.) 2, Cd(ox.)(succ.) and Cd(ox.) 2(succ.) have been evaluated by Schaap and McMasters' method; log β 12 = 4017, log β 21 = 4·982 ± 0·020 and a negative value for β 11. Cd(ox.)(succ.) probably does not exist in solution.

Electroanalytical study of cadmium-tyrosine complex at D.M.E.

Polarographic behaviour of Cadmium complex of tyrosine at D.M.E. has been investigated. The effect of change of pH, temperature, ligand concentration and height of mercury column on the wave characteristics has been studied and the results interpreted. The values of the stability constants of the complexes so formed have been calculated at 20±1°C and 30±1°C. Thermodynamic functions have also been evaluated.

Pyrimidine in aqueous media

The electrochemical reduction of pyrimidine in aqueous media was studied using alternating current (a.c.) polarography. Over the pH-range, 0.5–13, five moderately to highly irreversible a.c. waves were observed, which corresponded to the five waves observed on d.c. polarography. Although the electrochemical reduction path of pyrimidine is complex and only partially understood, good qualitative agreement between the features of the mechanism and various polarographic parameters was achieved, providing further support for the proposed mechanism, and indicating the validity of current theoretical and experimental results in the area of the a.c. polarography of quasi-reversible electrode reactions. Summit potentials for the five waves, which vary linearly with pH, are independent of applied alternating voltage, mercury column height (drop-time) and concentration, but shift to more negative potential with increasing frequency. Total alternating current for all waves increases linearly with amplitude of applied alternating voltage and the negative square root of droptime; plots of total alternating current vs. square root of applied frequency exhibit curvilinear trends with a maximum in the range, 15–50 Hz.

Alternating current polarographic behavior of pyrimidine in aqueous media

The electrochemical reduction of pyrimidine in aqueous media was studied using alternating current (a.c.) polarography. Over the pH-range, 0.5–13, five moderately to highly irreversible a.c. waves were observed, which corresponded to the five waves observed on d.c. polarography. Although the electrochemical reduction path of pyrimidine is complex and only partially understood, good qualitative agreement between the features of the mechanism and various polarographic parameters was achieved, providing further support for the proposed mechanism, and indicating the validity of current theoretical and experimental results in the area of the a.c. polarography of quasi-reversible electrode reactions. Summit potentials for the five waves, which vary linearly with pH, are independent of applied alternating voltage, mercury column height (drop-time) and concentration, but shift to more negative potential with increasing frequency. Total alternating current for all waves increases linearly with amplitude of applied alternating voltage and the negative square root of droptime; plots of total alternating current vs . square root of applied frequency exhibit curvilinear trends with a maximum in the range, 15–50 Hz.

Ece mechanisms as studied by polarography and linear sweep voltammetry

Analysis of electron-transfer-chemical reaction-electron-transfer (ECE) mechanisms by polarography and linear sweep voltammetry is discussed in the case where two well separated successive waves are observed. With polarography it is shown that for moderately fast first-order chemical reactions the limiting current of the second wave is inversely proportional to the square root of the mercury column height. With linear sweep voltammetry the same relation holds between peak current and sweep rate. These can be used as diagnostic criteria for ECE mechanisms. Furthermore, a new method using double potential scan is proposed for kinetic analysis of ECE systems. It allows second-order reaction kinetics as well as first-order ones to be readily determined.

Polarographic behaviour of hafxium(iv) in aqueousalcoholic mixtures

A polarographic study of hafnium, has been carried out in lithium chloride (0.1, 0.5 and 1 M) in 5%, 25%, 50% and 75% (v/v ethanol. One polarographic wave was observed corresponding to a one-electron process agreeing with the microcoulometric study carried out at constant potential and constant current. The observed wave is well-defined and useful analytically. The half-wave potentials have been measured against the saturated calomel electrode at different conditions of pH, temperature, and height of mercury column in the concentration range between 10 −3 and 5 · 10 −3 M. The values for the diffusion current constant and the peak potentials obtained in derivative polarography, are also given.

Polarographic Reduction of the Phenyl‐Substituted Ethenes: I . Relation of Postulated Mechanisms to Theoretical Behavior Patterns

The theoretically expected variations of the criteria of reversibility for electrochemical reduction, which have been proposed for inorganic systems on the basis of direct current polarography, have been developed for the various possible mechanisms, which might be expected for the reduction of the phenyl‐substituted ethenes at the dropping mercury electrode. These criteria of reversibility include the beta function (ratio of mean current to instantaneous current), the dependence of the current on the drop‐time (mercury column height), the slope of the plot of the familiar log current function, i.e., , and the variation of half‐wave potential in relation to proton availability. The situation for irreversible waves is considered on the basis of the equations derived for both the planar electrode and the expanding spherical electrode. Since the mechanisms considered are generalized approaches which can be applied to the reduction of various types of functionalities, both inorganic and organic, the equations developed and conclusions reached are of general utility.

Polarography of flavine mononucleotide and flavine adenine dinucleotide

Flavine coenzymes FMN and FAD were studied polarographically. Both flavines show well-defined reversible polarographic waves consisting of a normal reduction wave and a “post” wave due to adsorption. The half-wave potentials of the normal reduction wave correspond to the standard oxidation-reduction potentials determined potentiometrically. The polarographic results indicate the formation of semi-quinone. The semi-quinone formation constants were calculated by the “index potential” method. The electrocapillary curves were determined for both flavines. The nature of the adsorption wave was established by various criteria such as the variation of the wave heights with the mercury column height or temperature. The total diffusion wave height is in linear relationship with the depolarizer concentration. The E 1 2 vs. pH plot conforms to the theoretical equation and has two bends corresponding to the p K a values of the coenzymes.