We 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 as low as 1 parts per trillion can be detected using a 4-(mercaptoethyl)pyridinium monolayer. The different parameters that govern the analytical performance of these electrodes have been studied in detail and optimized. In addition, the organization of the monolayers has been examined by a variety of surface techniques such as XPS, FT-IR, and electrochemistry. Our results show that structuring and understanding the solid-liquid interface at the molecular level are essential for designing probes with superior analytical characteristics.[on SciFinder (R)]

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)]