Timer with memory to determine life of consecutive mercury drops

Papeschi, G.; Costa, Mariagrazia; Bordi, S.

doi:10.1016/0013-4686(70)85036-8

Cited by 20 publications

(11 citation statements)

References 6 publications

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“…The capillaries used either for drop-time measurements or for polarographic investigations were drawn from 2 • 10 mm Pyrex tubes and dewetted with di- apparatus and other experimental details were as described previously (16).…”

Section: Methodsmentioning

confidence: 99%

Electrochemical Behavior of Methylene Blue and Its Leucoform at the Mercury Electrode

Papeschi

Costa

Bordi

1981

J. Electrochem. Soc.

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The electrochemical behavior of methylene blue (MB) and its leucoform (LMB) in aqueous solutions at pH 7.9 was investigated with a mercury electrode. The polarographic results showed that at very low concentrations (4 • 10 .6 M/liter) and E1/z of "Brdi~ka's prewave" is the same as the standard potential of the MB/LMB couple and moves from about --0.290 to --0.180V (NCE) as the concentration increases. The electrocapillary curves indicate the following: (i) at low concentrations the LMB is less adsorbed than the MB; (ii) ~ decidedly decreases when the surface concentration of LMB reaches a value high enough to form a solid deposit on the mercury surface. We suggest that: (a) "Brdi~ka's prewave" which occurs at the lowest concentrations is actually the normal wave of the MB/LMB couple; (b) "Brdicka's normal wave" is a step that develops at the standard potential, but on an electrode covered by an insoluble film of LMB.The electroreduction of methylene blue (MB) to leucomethylene blue (LMB) on a mercury electrode takes place with an anomalous behavior. This system was studied polarographically by Brdi~ka (1, 2) and it is the classical example of reduction product adsorption cited in every textbook of polarography (3-5).Brdigka shows that at pH = 7.96 at concentrations of MB below 6 • 10-~M a single step ("prewave") is observed, while at higher concentrations a second step ("normal wave") appears at more negative potentials.In the interpretation of Brdi~ka the "prewave" corresponds to reduction of unadsorbed MB to adsorbed LMB; the height of this step is limited, not by the rate of diffusion of MB, but by the surface available for adsorption of the reduced molecules. He states that the product of MB reduction is adsorbed at the electrode surface as soon as it is formed and this facilitates, from an energy point of view, the reduction itself by allowing it to take place at a potential less negative than the standard potential of the MB/LMB couple. According to Brdi~ka, the "normal wave" is observed when the surface is fully occupied by LMB and requires a more negative potential since the reduced form finds itself in a higher energy state (unadsorbed as opposed to adsorbed). Under these conditions there is no process aiding the reduction and therefore the normal wave should develop in the neighborhood of the standard potential.After Brdi~ka much work was done (6-14) using different techniques in order to provide the MB/LMB redox couple with new information. Although the majority of these investigations have retained substantially unchanged Brdi~ka's point of view, experimental evidence exists and points out that the MB/LMB system is actually more complicated than Brdicka's scheme assumes it to be.Recently Baumgartner et aL (15) have shown by using multiple specular reflection spectroscopy applied to a thin layer electrochemical cell, that, in {he first 0.5 sec of the (I X 10-5M) MB reduction process, the LMB formed precipitates on the gold electrode surface.We are presenting here experimental evidence pertaining to th...

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Section: Methodsmentioning

confidence: 99%

Electrochemical Behavior of Methylene Blue and Its Leucoform at the Mercury Electrode

Papeschi

Costa

Bordi

1981

J. Electrochem. Soc.

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“…rely either on a photocell to detect an interrupted light beam as the drop falls (e.g., 35 ' 36 ' 37 ), or on electrical means, most often the detection of a sudden change in impedance coincident with drop dislodgement. 38 " 41 We designed a detector based on the latter principle: A sinusoid of 1, 2, 5 or 10 mV peak-to-peak amplitude oscillating at 100 kHz is impressed on the cell atop the applied voltage. The cell current taken from the I/E converter is then amplified, filtered, frequency-doubled, and rectified.…”

Section: A(drop Time) Electrosorptive Detectionmentioning

confidence: 99%

Instrumental Methods for Electrosorptive Detection in Liquid Chromatography

Ramstad¹,

Milner²

1989

Instrumentation Science & Technology

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Techniques and instrumentation have been developed for the electrosorptive detection of selected anions at mercury and silver in ion chromatography and of surface-active organic substances at mercury. Detection based on differential double-layer capacitance has proven most generally useful, although pulsebased methods are also beneficial, especially at silver where they have special utility in countering adsorption effects. An ancillary, and more specialized technique developed for the determination of ions senses adsorption, indirectly, relying on the kinetic facilitation imparted the rate of electroreduction of a transition-metal reactant by an adsorbed species. A less generally useful, but nevertheless complementary scheme based on the "tensammetric" peak may also be employed for the determination of organic species. A novel approach investigated for application Present address: The Upjohn Company, Kalamazoo, Michigan Present address: Isco Inc., Lincoln, Nebraska r 148 RAMSTAD AND MILNER to both ionic and neutral species is based on changes in the drop time of mercury caused by adsorption-induced changes in surface tension at the mercury/aqueous interface. Finally, more elaborate, "hyphenated" techniques -capacitive/capacitive and capacitive/amperometric detection -have also been developed for application to selected ions.

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“…The passband has been settled at 1.5 kHz to ensure best noise rejection, compatibly with the required response time (0.5 msee). Then, the signal, rectified by a full-wave circuit, instead of being compared with a fixed reference level as usual (i, [3][4][5], is split into two paths ( Fig. 2): in one of them, the signal is integrated, and inverted, in the other, it is differentiated.…”

Section: Description Of the Circuitmentioning

confidence: 99%

“…Lawrence and Mohilner (4) have proved the absence of any perturbation due to the a-c signal on the interface, and various circuits have been described (1,3,5).…”

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confidence: 98%

High Reliability Drop‐Fall Detector for Computerized Drop‐Time Measurements

Carlà

Aloisi

Papeschi

et al. 1983

J. Electrochem. Soc.

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An electronic drop-fall detector for dropping mercury electrodes is described. The device has been conceived to work in a computer controlled apparatus. It offers an accuracy better than 500/Lsec and a false triggering rate better than one error over 104 drops.A fully computer controlled apparatus for electrocapillary measurements by the drop-time method has been assembled in our laboratory. It has been conceived to work continuously for several days unattended; thus, a drop-fall detector was needed with:(i) high accuracy, (ii) high noise immunity, and (iii) no need of trimming along a full run, even with solutions of different conductivity. A brief review of the available techniques, with a comparative analysis, can be found in Ref. (1-3).We agree with Tyma (1) in considering the technique based upon a-c impedance measurements as being at present the most suitable one. Lawrence and Mohilner (4) have proved the absence of any perturbation due to the a-c signal on the interface, and various circuits have been described (1, 3, 5).However, features (ii) (i.e., the insensitivity to statics and to the electromagnetic disturbances generated by the other laboratory apparatus) and (iii) (i.e., the ability to work properly for a long time without loss of performances even when solutions of very different conductivity are used) are hardly at-* Electrochemical Society Active Member.

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Timer with memory to determine life of consecutive mercury drops

Cited by 20 publications

References 6 publications

Electrochemical Behavior of Methylene Blue and Its Leucoform at the Mercury Electrode

Electrochemical Behavior of Methylene Blue and Its Leucoform at the Mercury Electrode

Instrumental Methods for Electrosorptive Detection in Liquid Chromatography

High Reliability Drop‐Fall Detector for Computerized Drop‐Time Measurements

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