Routine analysis by high precision gas chromatography/mass selective detector/isotope ratio mass spectrometry to 0.1 parts per mil

Stable isotope methods are potentially quite useful for validating natural or enhanced mineral degradation of contaminants. For this reason, a continuous flow gas chromatograph (GC), isotope ratio mass spectrometer (IRMS) has been coupled with a quadrupole mass selective detector (MSD) to allow simultaneous mass spectral and stable carbon isotope ratio data to be obtained from a single chromatographic analysis. This allows the target contaminant and any extra-cellular degradation intermediates to be both qualified and quantified. Previously acceptable limits of precision (0.3 parts per mil) are undesirable given the small fractionation observed during aerobic degradation. To further understand the fate of organic contaminants and to gain information about the metabolic degradative pathway employed by a microorganism, routine isotopic analyses on a range of analytes have been performed. Quantities of sample producing mass-44 ion beam signal (I(44)) of 2 x 10(-10) to 1 x 10(-8) A were analysed. When the IRMS was tuned for high sensitivity, ion source nonlinearities were overcome by peak height correction from an algorithm that was produced using known isotopic standards of varying concentrations. This led to sample accuracy of <0.01 per thousand and sample precision of 0.1 per thousand. Copyright 1999 John Wiley & Sons, Ltd.     

Chalcogen-chalcogen bonds in edge-sharing square-planar d8 complexes. Are they possible?

A theoretical study of the formation of X-X bonds in complexes with the general formula [M(2)(mu-X)(2)L(4)] (M = group 10 and X = group 16 elements) having d(8) transition-metal atoms is presented. The existence of two energy minima for some complexes, with short and long X-X distances, is shown by density functional theory calculations, and the factors responsible for it are analyzed, including a strong influence of the nature of the metals and ligands on the relative stability of the two isomers. The influence of the bite angle of chelating terminal ligands and the nature of the donor atom on the relative stabilities of the two isomers are also discussed.     

Laser beam deflectometry and C60 polymerized nanorods dynamics by surface interdiffusion

Laser beam deflectometry was used to follow the growth dynamic of C₆₀ nanorods via an interfacial diffusion and self-assembly phenomenon. The deduced average value of the interfacial diffusion coefficient D_int from the refractive index gradient was found to be of the order of 3.32 10^? 6 m²/s.     

Valency control in MoO<Subscript>3−δ</Subscript> nanoparticles generated by pulsed laser liquid solid interaction

The possibility of synthesizing binary oxides nanoparticles in a nano-scaled form by laser liquid solid interaction using a NdYAG “1.064 μm” as an irradiating laser source is reported. The case of MoO_3−δ is emphasized. Furthermore, it is demonstrated that the Mo–O electronic valence can be controlled through the coupling effects of oxygen enriched nature of the used coating liquid layer, namely pure H₂O or H₂O₂ and the laser beam fluence. Dark blue hydrated molybdic pentoxide Mo₂O₅·xH₂O and yellow molybdenum trioxide MoO₃ nano-suspensions were reproducibly synthesized with hydrogen peroxide and water, respectively, at a relatively high ablation rate. The average size of the molybdenum trioxide nanoparticles was about <ϕ>~8 nm, slightly larger than the molybdic pentoxide ones “<ϕ>~6.2 nm”.     

The influence of laser annealing in the presence of longitudinal weak magnetic field on asymmetrical magnetoimpedance response of CoFeSiB amorphous ribbons

Asymmetrical magnetoimpedance (AMI) is very important to further improve micromagnetic sensor performance in terms of linearity and sensitivity. This behavior was investigated for Co_68.15Fe_4.35Si_12.5B₁₅ amorphous ribbons irradiated by a 1064 nm Nd:YAG pulsed laser in air and in the presence of 3 Oe longitudinal magnetic field with changing pulse repetition rate. Results indicate that for different pulse repetition rates, various types of AMI profiles appear. For the samples annealed in the presence of longitudinal field, because of induced anisotropy, rising in asymmetry factor takes place and another peak in the magnetoimpedance (MI) profile transpires.     

Magneto-optical Kerr effect in glass/Cu/CoFeSiB/SnO2 thin films

We report on the Kerr signal enhancement as a result of the capping effect of SnO₂ on the CoFeSiB amorphous layer. The magnetic layer was deposited by pulsed laser deposition method on Cu buffer layer and was capped by SnO₂ with different thicknesses. The magnetic behavior of the samples was investigated by the Kerr effect. As the SnO₂ thickness increased up to about 70 nm, the Kerr signal increased and then reduced. The results were analyzed using the formalism based on the matrix method.     

Experimental design as an optimization approach for fabrication a new selective sensor for thallium(I) based on calix[6]arene

The performance of a new membrane sensor based on polyvinyl chloride (PVC) for Tl(I) assay was investigated using the statistical design as an optimization strategy. The Plackett-Burman and Box-Behnken designs, respectively, were utilized to find out the influencing variables and optimization of conditions. In order to evaluate the relationship between the responses of electrode (slope) and significant variables along with their interactions, a mathematical model was presented. The interactions between significant variables were intuitively illustrated according to the response surface plots. Apart from that, the optimum conditions as a result of response surface methodology for both membrane ingredients and measuring conditions such as pH, PVC, internal solution concentration, calix[6]arene, 2-nitrophenyloctylether, potassium tetrakis-(p-chlorophenyl)borate and time conditioning, respectively, were found to be: 6, 0.028 g, 0.001 M, 0.0035 g, 0.065 g, 0.0015 g and 20 h. The optimized sensor exhibits a Nernstian response for thallium(I) over a wide linear range from 2.0 × 10^?6 to 2.0 × 10^?2 M and the slope of 57.9 ± 0.1 mV/decade of the activity and limit of detection (LOD) 1.9 × 10^?5 M. The relative standard deviations (RSD) for six replicates of the measurement at 1 × 10^?5 and 1 × 10^?5 M of Tl(I) were 2.7 and 3.0%, respectively. The favorable results were given through the direct determination of Tl(I) in spiked wastewater and artificial spiked urine sample with Tl(I). The electrode was also successfully applied to the titration of a Tl(I) solution with KI.     

Elucidation of diazinon metabolites in rice plants by liquid ‎chromatography ion-trap mass spectrometry

ABSTRACT

A fast, selective and sensitive reversed-phased liquid chromatography coupled to ion-trap mass spectrometry has been developed to elucidate and confirm the diazinon metabolites with a wide range of polarity in the rice plant samples. Sample extraction and purification were performed with a QuEChERS-based (Quick, Easy, Cheap, Effective, Rugged, and Safe) procedure. To boost all metabolism sensitivities, all rice extracts were concentrated under vacuum to near dryness and taken up into initial mobile phase. Careful optimisation of the LC–MS/MS parameters were achieved in order to attain a fast separation with the best sensitivity. The detection was carried out on an ion-trap mass spectrometer by electrospray ionisation in positive ion mode (ESI+) with multiple reaction monitoring.     

Multi-objective optimization of pin fin to determine the optimal fin geometry using genetic algorithm

In this study, one dimensional heat transfer in a pin fin is modeled and optimized. We used Bezier curves to determine the best geometry of the fin. The model equations are solved to analyze the heat transfer. Total heat transfer rate and fin efficiency factor are considered as two objective functions and multi-objective optimization carried out to maximize heat transfer rate and fin efficiency simultaneously. Fast and elitist non-dominated sorting genetic algorithm (NSGA-II) is used to determine a set of multiple optimum solutions, called ‘Pareto optimal solutions. The optimized results are presented with Pareto front which demonstrate conflict between two objective functions in the optimized point, both energy conservation and thermal analysis are carried out to verify the solution method and the results shows good precision.