Anodic stripping voltammetry with a glassy carbon electrode mercury-plated in situ

The physiology and biochemistry of many taxa inhabiting deep-sea hydrothermal vents have been elucidated; however, the physicochemical factors controlling the distribution of these organisms at a given vent site remain an enigma after 20 years of research. The chemical speciation of particular elements has been suggested as key to controlling biological community structure in these extreme aquatic environments. Implementation of electrochemical technology has allowed us to make in situ measurements of chemical speciation at vents located at the East Pacific Rise (9 degrees 50' N) and on a scale relevant to the biology. Here we report that significant differences in oxygen, iron and sulphur speciation strongly correlate with the distribution of specific taxa in different microhabitats. In higher temperature (> 30 degrees C) microhabitats, the appreciable formation of soluble iron-sulphide molecular clusters markedly reduces the availability of free H2S/HS- to vent (micro)organisms, thus controlling the available habitat.

Chemical speciation drives hydrothermal vent ecology.

Measurement of enzyme E'values by optically transparent thin layer electrochemical cells.

Seasonal iron cycling in the salt-marsh sedimentary environment: the importance of ligand complexes with Fe(II) and Fe(III) in the dissolution of Fe(III) minerals and pyrite, respectively

A biogeochemical cycle is proposed for the reactivity of iron in salt-marsh sediments. The main reactions of the iron cycle are: (1) solubilization of Fe(III) by organic ligands; (2) reduction of soluble Fe(III) to Fe(II) by these ligands, soluble reduced sulfur or solid phase reduced sulfur, (3) the oxidation of the resulting Fe(II) (complexed to organic chelates) by Fe(III) minerals; (4) the formation of iron sulfide minerals when dissolved sulfide is in excess. The cycle of iron solubilization will continue as long as bacteria and/or plants produce organic ligands

Seasonal iron cycling in the salt-marsh sedimentary environment : the importance of ligand complexes with Fe(II) and Fe(III) in the dissolution of Fe(III) minerals and pyrite, respectively

Controlled-potential polarography has been exploited in the versatile controlled-potential and derivative polarograph. An amplifier continuously forces the potential of the polarized electrodc with respect to the reference electrode to equal that of the linearly inereasing control potential independently or circuit and of cell resistances. Controlled-potential pularography is espeeially suitable for high resistance media or for high current polarography in aqueous media where polarograms on ordinary instruments suffer distortion. because of iR drop in the electrolyte. The polarograph can be used for the analysis of irreversible and reversible species at very low conccntrations. It is possible to record the instantaneous currents, the successive peak currents, the successive average currents, easr the time derivative of the polarographic wave as a function of the potential of the polarized electrode with respect to the solution. Regular and derivative polarograms are presented that illustrate the advantage of controlled-postential over conventional polarography. (auth)

Controlled-potential and derivative polarograph

A simple electronic instrument for coulometric redox titrations at controlled potential is described. The potential of only the eleclrode at which the desired reaction occurs is controlled by a stabilized difference amplifier combined with a transistor current amplifier. The electrolysis current is integrated by a stabilized amplifier. The integral is read out as a voltage. Either manual or automatic titrations may be made. The instrument is alternating current line-operated. It is very stable and gives titration results of good precision which are obtained by calculation from Faraday's law. (auth)

Electronic controlled-potential coulometric titrator

A polarographic polarizing unit is described that has electronic scan. linear residual current compensation. and potential-control circuits. The performance of the electronic-scan circuit is superior to that of a conventional motor-driven multiturn pctentiometer scanner. The use of this polarizing unit is particularly advantageous for highsensitivity polarography, both regular and derivative.

H. C. Jones

Papers

Controlled-potential and derivative polarograph

Electronic controlled-potential coulometric titrator

Controlled-potential polarographic polarizing unit with electronic scan and linear residual current compensation

Apparatus for precision control of drop time of dropping mercury electrode in polarography

Solid-state controlled-potential d.c. polarograph with cyclic scanning and calibrated first- and second-derivative scales