On the vibrational behaviour of cyanide adsorbed at Pt(1 1 1) and Pt(1 0 0) surfaces in alkaline solutions

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(1 1 1) and Pt(1 0 0) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C-N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(1 1 1)-CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C-N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.     

New techniques to evaluate the incendivity of insulators

New techniques for evaluating the incendiary behavior of insulators is presented. The onset of incendive brush discharges in air is evaluated using standard spark probe techniques for the case simulating approaches of an electrically grounded sphere to a charged insulator in the presence of a flammable atmosphere. However, this standard technique is unsuitable for the case of brush discharges that may occur during the charging–separation process for two insulator materials. We present experimental techniques to evaluate this hazard in the presence of a flammable atmosphere which is ideally suited to measure the incendiary nature of micro-discharges upon separation, a measurement never before performed. Other measurement techniques unique to this study include: surface potential measurements of insulators before, during and after contact and separation, as well as methods to verify fieldmeter calibrations using a charge insulator surface opposed to standard high voltage plates.     

Voltammetric studies of a psychotropic drug with nitro groups. Determination of flunitrazepam in urine using HMDE

The adsorption behaviour of flunitrazepam at the hanging mercury drop electrode was studied by staircase voltammetry and by adsorptive stripping differential pulse voltammetry. Flunitrazepam is adsorbed in the whole potential range, from the most positive values up to the reduction potential. Flunitrazepam reduction product is also adsorbed. The time dependence of the voltammetric response proves that a diffusion-controlled adsorption takes place. Flunitrazepam can be determined (down to nanomolar levels) by using adsorptive preconcentration prior to the differential pulse voltammetric scan. An application of such a method to flunitrazepam determination in human urine is described. The detection limit was 30 ng per milliliter of urine with a 20-sec accumulation time; the mean relative standard deviation was lower than 3.2% and the mean recovery 97.8%.     

Characterization and deposition of various light-harvesting antenna complexes by electrospray atomization

Photosynthetic organisms have light-harvesting complexes that absorb and transfer energy efficiently to reaction centers. Light-harvesting complexes (LHCs) have received increased attention in order to understand the natural photosynthetic process and also to utilize their unique properties in fabricating efficient artificial and bio-hybrid devices to capture solar energy. In this work, LHCs with different architectures, sizes, and absorption spectra, such as chlorosomes, Fenna–Matthews–Olson (FMO) protein, LH2 complex, and phycobilisome have been characterized by an electrospray-scanning mobility particle-sizer system (ES-SMPS). The size measured by ES-SMPS for FMO, chlorosomes, LH2, and phycobilisome were 6.4, 23.3, 9.5, and 33.4?nm, respectively. These size measurements were compared with values measured by dynamic light scattering and those reported in the literature. These complexes were deposited onto a transparent substrate by electrospray deposition. Absorption and fluorescence spectra of the deposited LHCs were measured. It was observed that the LHCs have light absorption and fluorescence spectra similar to that in solution, demonstrating the viability of the process.     

Highly efficient quenching of nanoparticles for the detection of electron‐deficient nitroaromatics

Reported herein is the highly efficient quenching of fluorescent organic nanoparticles by 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene. These fluorescent nanoparticles are formed from the hydrophobic collapse of fluorescent polymer chains and display quenching efficiencies that are in line with the highest reported literature values. Moreover, the fluorescent quenching occurs only for the fluorescent nanoparticles, and not for the precursor polymer solutions, which display marked insensitivity to the presence of nitroaromatics. This aggregation‐dependent fluorescent quenching has numerous applications for the detection of small‐molecule electron‐deficient analytes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4150–4155     

Chemical modifiers in arsenic determination in biological materials by tungsten coil electrothermal atomic absorption spectrometry

Palladium, iridium, and rhodium are evaluated as possible chemical modifiers in the determination of As in digest solutions of biological materials (human hair and clam) by tungsten coil electrothermal atomic absorption spectrophotometry (TCA-AAS). The modifier in solution was applied onto the coil and thermally pre-reduced; the pre-reduction conditions, the amount of modifier, and the thermal program were optimized. Palladium was not satisfactory, whereas Ir and Rh were effective modifiers and rendered better relative sensitivity for As by a factor of 1.4 and 1.9, respectively compared to the case without modifier. Upon optimization of thermal conditions for As in pre-reduced Ir (2.0 µg) and Rh (2.0 µg) modifiers and in the digest solutions of the study matrices, Rh (2.0 µg) was more effective modifier and was selected as such. The mean within-day repeatability was 2.8% in consecutive measurements (25–100 µg L^–1) (3 cycles, each of n=6) and confirmed good short-term stability of the absorbance measurements. The mean reproducibility was 4.4% (n=20 in a 3-day period) and the detection limit (3 _blank/slope) was 29 pg (n=15). The useful coil lifetime in Rh modifier was extended to 300–400 firings. Validation was by determination of As in the certified reference material (CRM) of Oyster tissue solution with a percentage relative error (E _rel%) of 2% and percentage relative standard deviation (RSD%) of 3% (n=4), and by analytical recovery of As spiked in CRM of human hair [94±8% (n=4)]. The methodology is simple, fast (sample readout frequency 21 h^–1), reliable, of low cost, and was applied to the determination of As in hair samples of exposed and unexposed workers.