A highly sensitive assay for the detn. of Cr(VI), in the presence of Cr(III) and in the presence of other cations by cyclic voltammetry. The detn. is carried out with a gold or gold-plated electrode with a self-assembled monolayer of a pyridine deriv. of the kind of 4-(2-ethanethiol) pyridine. Detns. can be effected at extremely low levels of the order of 1 ppt (part per trillion, 1012). [on SciFinder(R)]

The authors have developed a selective electrode for chromium(VI), based on a self-assembled monolayer of 4-(mercapto-n-alkyl)pyridinium on gold surfaces, which exhibits unique speciation capabilities. Cr(VI) levels ≥1 parts per trillion can be detected using a 4-(mercaptoethyl)pyridinium monolayer. The different parameters that govern the anal. performance of these electrodes were studied in detail and optimized. The organization of the monolayers was examd. by a variety of surface techniques such as XPS, FTIR, and electrochem. Structuring and understanding the solid-liq. interface at the mol. level are essential for designing probes with superior anal. characteristics. [on SciFinder(R)]

A disorganized monolayer of ω-mercaptoalkanesulfonic acid, HS(CH2)nSO3H, serves as selective mol. sieve, which is selectively permeable to electroactive species. Due to the strong acidity of the sulfonic acid moiety the monolayers are highly charged in aq. soln. throughout most of the pH range. Cyclic voltammetry of neg. charged inorg. species, such as hexacyanoferrate, clearly shows the repulsion of these species from the solid-liq. interface. Cyclic voltammetry of pos. charged ions, e.g., hexaammineruthenium(III), is not influenced at all by the presence of a mercaptodecanesulfonic acid monolayer, suggesting a partial coverage of the gold substrate by the monolayer. Fe(III) ions were detd. by Osteryoung square wave voltammetry in the presence of both inorg. anions and sol. org. species. [on SciFinder(R)]

The initial stages of the anodic oxidn. of Au(111) were studied by cyclic voltammetry as well as in situ scanning tunneling microscopy (STM). Probably the place exchange process, which initiates the oxide formation, starts at step edges. The oxide phase was imaged in situ by scanning tunneling and at. force microscopy (AFM). The topog. information acquired by the two techniques is compared. [on SciFinder(R)]

Self-assembled monolayers (SAMs) of ω-mercaptoalkanesulfonic acid on Au surfaces were studied by electrochem. and other surface techniques. In spite of the fact that these monolayers are disorganized, i.e., of brush type, they are impermeable to inorg. anions due to their high neg. charge. Also, an ω-mercaptodecanesulfonic acid (MDS) monolayer is also impermeable to org. species, regardless of their charge, because of its high hydrophilicity. The combination of these properties made it possible to apply Au electrodes modified with MDS for the detn. of Fe(III) ions in the presence of org. species that are either electroactive throughout the same potential window or form strong complexes with Fe(III). [on SciFinder(R)]

Visualized fingerprints on unfired brass cartridge cases developed by a novel method of palladium deposition were examd. by Auger electron spectroscopy (AES), SEM, and electron probe microscopy (EPMA). In spite of the strong contrast of colors between the ridges and the valleys of the developed images, which suggests a selective coating of palladium on the valleys, palladium was found to deposit onto both valleys and ridges. Lumps of org. material were scattered mostly along the ridges. The study suggests a model for the deposition of metals on brass cartridges on which sebaceous fingerprints were impressed. [on SciFinder(R)]

At. force microscope (AFM) was used to examine aluminum sample prepn., electropolishing and anodic dissoln. The anodic dissoln. of Al was studied in ammonium tartrate and sulfuric acid. Smoothening or roughening of the surface was imaged and depends primarily on the time, potential and type of electrolyte. [on SciFinder(R)]

A review with 69 refs. The different approaches in which self-assembled monolayers (SAMs) were applied in electroanal. chem. are reviewed. Three principal concepts were used and can be categorized according to the mechanism of attachment of the monolayer to the electrode. These include the formation of covalent bonds between reactive org. mols., such as chlorosilanes, with activated surfaces, the formation of lipid and bilayer lipid membranes that self-assemble on conductive surfaces and the adsorption of functionalized alkanes, e.g., alkanethiols, on well ordered surfaces. Systems for detecting inorg., org. and biol. species are described and conclusions are drawn. [on SciFinder(R)]

A review with 23 refs. The scanning electrochem. microscope (SECM) is one of the scanning probe techniques that were developed following the introduction of the scanning tunneling microscope. The approaches that were used to modify surfaces with lateral resoln. using the SECM are presented and discussed. These approaches made it possible to drive a variety of microelectrochem. reactions on surfaces, as well as to study the mechanism of these processes due to the unique advantages that the SECM offers. [on SciFinder(R)]

A method of scanning electrochem. microscope (SECM) was used to analyze the kinetics of the charge transfer at the liq./liq. interface. The method overcomes a limitation requiring a sepn. of ion transfer process from the charge transfer process. Few exptl. results involving iridium and iron complexes are discussed. [on SciFinder(R)]

The adsorption of L-cysteine on Au(111) from a perchlorate soln. was studied by in-situ scanning tunneling microscopy. The potential-induced adsorption of the thiols lifts the reconstruction of Au(111) and at more pos. potentials L-cysteine adopts a definite adlayer structure. The potential-induced desorption of the adlayer does not cause the reconstruction to reappear but instead leaves a roughened surface with a large no. of monoat. high gold islands and monoat. deep holes. [on SciFinder(R)]

The formation and organization of self-assembled monolayers of alkanethiols and ω-mercaptocarboxylic acids on Hg surfaces were studied. The organization process was examd. in-situ and ex-situ by cyclic voltammetry. Charging current measurements as well as electron transfer expts. with Ru(NH3)63+/2+ indicate that the adsorption of homologous alkanethiols and ω-mercaptocarboxylic acids on Hg is followed by the formation of a densely packed array. [on SciFinder(R)]

The organization of chiral self-assembled monolayers (SAMs) composed of a thiol deriv. of phenylalanine on a hanging mercury drop electrode (HMDE) has been studied. Comparing the excess of surface coverage of homo and heterochiral monolayers reveals that the latter are more densely packed. This was also supported by examn. the differential capacitance and the electrochem. behavior of an outer-sphere redox couple at surfaces covered by homochiral monolayers vs. monolayers based on the racemic mixt. [on SciFinder(R)]

A highly specific and sensitive electrode for the detn. of ultra-low levels of Hg and an anal. system based on such electrode are described. The electrode is a glassy C electrode spin-coated with a monolayer of a highly sensitive reagent for the detection of Hg. The anal. method based on the use of this type of electrode is a voltammetric method. Concns. of the order of as low as ∼2 × 10-12 Mol Hg can be detected and measured. The reagent is 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane. [on SciFinder(R)]

The deposition of gold patterns on indium-tin-oxide (ITO) with the scanning electrochem. microscope (SECM) has been accomplished by the controlled dissoln. of a gold microelectrode. The continuous anodic dissoln. of gold at the microelectrode in the presence of bromide while maintaining the potential of the ITO const. resulted in the deposition of microcryst. structures of gold. The unique advantages of the SECM made it possible to suggest a mechanism for the process based on the structures as well as the parameters that control the deposition process. [on SciFinder(R)]

The etching of silicon has been studied by the scanning electrochem. microscope (SECM) technique. Etching has been accomplished in acidic fluoride solns. by electrogenerating a strong oxidant, i.e. bromine in this case, at an ultramicroelectrode which was held closely above a silicon 〈111〉 wafer. The parameters that affect the process and control the efficiency of the silicon etching were examd. A detailed mechanism of the process, which was derived from the unique advantages of the SECM and is in agreement with previous reports, is proposed. [on SciFinder(R)]

A detailed study of the Cd(II)/Cd(Hg) system in 2-mercaptoacetic acid, H2MA, solns. was carried out in 1 M NaClO4 at pH 4.8-12.0. The electrochem. behavior of 2-mercaptoacetic acid at a dropping mercury electrode was studied as well. Since all complexes that are formed in the soln. undergo a reversible two-electron redn., math. anal. of the data, provided the compn. of the various complexes. The stability consts. of the following complexes: Cd(SCH2CO2)34-, Cd(SCH2CO2)22-, Cd(SCH2CO2), CdH(SCH2CO2)33-, CdH2(SCH2CO2)32-, CdH(SCH2CO2)2-, CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ were detd. and their degree of formation as a function of pH were estd. The protonation consts. of the ligand were calcd. The H2MA forms extremely stable bidentate complexes with cadmium ions. The formation of the various complexes as a function of pH reveals that at pH 10.7-12.0 the complex Cd(SCH2CO2)34- predominates, whereas at pH 4.8-6.0 the complexes CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ are dominant. At pH 6.1-10.6 different protonated and unprotonated complexes, composed of one to three ligands, coexist. [on SciFinder(R)]

Selective electrodes are electrochem. probes which are sensitive toward specific species. Most of these probes can be divided into two categories, i.e. potentiometric and voltammetric, based on the nature of the measurement. The major challenge is designing a selective electrode is introducing selectivity. The ultimate limit of their selectivity should make it possible to det. the levels of the analyte in unpolluted sea water. Through this manuscript two different approaches have been used as a means of developing voltammetric selective electrodes for heavy metals. The first concept involves the application of electrodes modified with crown ethers analogs. A selective electrode for gold ions was assembled by attaching an aza crown ether onto a glassy carbon surface. On the other hand an extremely sensitive electrode for mercury ions was developed based on a cryptand. Levels of mercury lower than 1 ppt could easily be detected using this probe. The electrode has been successfully applied for studying the release of mercury from dental amalgam. The second approach involves the formation of self-assembled monolayers with high affinity toward specific species. As an example, a selective electrode for cadmium ions is described. The electrode is made of ω-mercaptocarboxylic acid, HS(CH2)nCO2H, monolayers on mercury or gold surfaces. The detection limit of this electrode is 4 x 20̅12 M which is less than 1 ppt. The electrodes have been carefully studied and the parameters that govern their sensitivity as well as selectivity were optimized. Our major conclusion from this research is that very selective and sensitive probes can be developed by architecturing the solid-liq. interface at the mol. level. [on SciFinder(R)]