74 research outputs found
Observation of gas-phase molecular dications formed from neutral organics in solution via the controlled-current electrolytic process inherent to electrospray
This article reports the first electrospray (ES) mass spectrometry observation of molecular dications that were formed in solution by sequential one-electron oxidation of the neutral molecules [viz., nickel(II) and cobalt(II) octaethylporphyrin] via the controlled-current electrolytic (CCE) process inherent to electrospray. Dication formation was found to require (1) the addition of electrolyte to the sample solution, which increased the magnitude of the ES current and, therefore, increased the extent of analyte electrolysis in the ES capillary, (2) a relatively low solution flow rate, which increased the electrolysis time (i.e., the time the analyte remained in the capillary), thereby providing more time for the analytes to diffuse to the metal-solution interface and react, and (3) the use of a platinum ES capillary, which, because it is difficult to oxidize, increased the proportion of the faradaic current that might be provided by electrolysis of solution species compared to that proportion available when the typical stainless steel capillary is used. These interpretations of the data are made on the basis of the known characteristics of the CCE process inherent to ES, supplementary data obtained from direct solution-phase observation of the metalloporphyrin redox products formed within the different metal ES capillaries by means of a novel ES ion source, and off-line cyclic voltammetry studies of the metalloporphyrins performed by using platinum and stainless steel working electrodes
Selective Determination of Methylmercury by Flow-Injection Fast-Scan Voltammetry
A simple flow-injection system, suitable for solution flow rates at microliters-per-minute, has been combined with fast-scan voltammetry for selective determination of methylmercury. A thin Hg film was formed at a Pt microelectrode prior to the measurement. Detection of methylmercury is carried out by measuring the oxidation of methylmercury radicals that have been generated at the Hg microelectrode. At slow scan rates, the electrogenerated methylmercury radicals undergo a follow-up dimerization reaction to form dimethyldimercury (ErCi2 mechanism). At fast scan rates, it was found that methylmercury radicals can be quantitatively reoxidized (reversible electron-transfer). Optimization of the experimental conditions of the system was performed based on studies of the relationship between the scan rate and the dimerization rate of the methylmercury radical. Under optimized conditions, detection level of subnanomole was obtained with a sample consumption of less than 10 μL and the concentration detection limit for methylmercury at 50 V/s was estimated to be about 0.56 μM. To demonstrate the applicability of this method to automatic analyses, repetitive fast-scan cyclic voltammetry was conducted in conjunction with multiple sample injections. Determination of methylmercury in the presence of excess inorganic mercury was also conducted. This new approach to methylmercury determination was successfully applied to the analysis of elevated dogfish muscle samples
Postcolumn Renewal of Sensor Surfaces for High-Performance Liquid Chromatography−Surface Plasmon Resonance Detection
Polyelectrolyte Hollow Sphere Lithographic Patterning of Surfaces:Â Construction of 2-Dimensional Well-Ordered Metal Arrays
Silver-Enhanced Imaging of DNA Hybridization at DNA Microarrays with Scanning Electrochemical Microscopy
Redox Reactions of and Transformation between Cysteine−Mercury Thiolate and Cystine in Metallothioneins Adsorbed at a Thin Mercury Film Electrode
Surface Structure and Coverage of an Oligonucleotide Probe Tethered onto a Gold Substrate and Its Hybridization Efficiency for a Polynucleotide Target
α-Synuclein in α-helical conformation at air–water interface: implication of conformation and orientation changes during its accumulation/aggregation
a-Synuclein, a natively unstructured protein important in the neuropathology of Parkinson’s disease, was found to form a Langmuir monolayer in an a-helical conformation with its helical axis parallel to the air–water interface. This study sheds light on the role of vesicles in neuronal cells in the accumulation/aggregation of a-synuclein
Quantification of Redox-Induced Thickness Changes of 11-Ferrocenylundecanethiol Self-Assembled Monolayers by Electrochemical Surface Plasmon Resonance
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