High Rydberg resonances in dielectronic recombination of pb(79+)

Dielectronic recombination resonances of Pb (79+) associated with 2s(1/2)-->2p(1/2) excitations were measured at the heavy-ion storage ring ESR at GSI. The fine structure of the energetically lowest resonance manifold Pb (78+)(1s(2)2p(1/2)20l(j)) at around 18 eV could partially be resolved, and rate coefficients on an absolute scale were obtained. A comparison of the experimental data with results of a fully relativistic theoretical approach shows that high-angular-momentum components up to j=31/2 significantly contribute to the total resonance strength demonstrating the necessity to revise the widespread notion of negligible high-angular-momentum contributions at least for very highly charged ions.     

Correction parameters in X-ray fluorescence analysis applying the limit dilution method (LDM)

Summary Some corrective parameters: H, M, Y and Y/H are defined from the mathematical development justifying the Limit Dilution Method (LDM) in XRF analysis. These corrective parameters, for a given diluent and dilution, are characteristic of the analyte in each sample. The influence of these parameters on important phenomena such as the diluent effect is evaluated by a theoretical model. Using parameters Y, an algorithm is proposed which corrects the diluent effect and establishes linear functions of fluorescence intensity vs. analyte concentration. This paper also proposes a selection procedure for the optimum standard for a given problem using the Y/H parameter. The method is applied to the XRF analysis of mixtures of iron and zirconium oxides and these results show the corrective action of the suggested parameters and the appropriateness of the selection of the standards.     

The decay of the isotopes176Ir and177Ir

^176,177Ir were produced by irradiation of¹⁴¹Pr with⁴⁰Ar. β-delayed γ-rays of^176,177Ir were observed for the first time. From γγ-coincidence data decay schemes could be constructed. A new half-life of¹⁷⁷Ir was obtained yielding t_1/2=30 (2) s. α-branching ratios of 3.1(6) % for¹⁷⁶Ir and 0.06(1)% for¹⁷⁷Ir were measured.     

Effluent analysis in analytical chemistry: an overview

This review summarizes and discusses effluent analysis, focusing on the methods and techniques that have been most frequently described in the literature since 1975. The methods are classified into four main categories: (1) physical and chemical properties; (2) inorganic metals analysis; (3) inorganic non-metallic analysis; (4) organic analysis.     

The B-N bond controls the balance between locally excited (LE) and twisted internal charge transfer (TICT) states observed for aniline based fluorescent saccharide sensors

Three boronic acid based saccharide sensors with an aniline fluorophore have been prepared. One of the systems (1a) contains an intramolecular boron-nitrogen (B-N) bond and displays fluorescence due to both LE and TICT states. The other two systems (1b and c) have no B-N bond and only show fluorescence due to the LE state.     

New brassinosteroid analogs having nitrogenated functionalities at C3 to provide more information about the brassinosteroid-receptor interaction

An efficient synthesis of different brassinosteroid derivatives with an azide or an amine function at C3 without any function at C2 and their biological activity evaluation in the rice lamina inclination test is described. The key step in the synthetic strategy involves a nucleophilic substitution by azide of an activated 3β-OH followed by reduction to amine. The activity elicited by 7 and 9 having an azide group, in contrast with the residual ones elicited by their corresponding amines, suggests that the 3α-OH group of an active brassinosteroid could act as acceptor in the putative hydrogen bonding interaction with the receptor/s.     

Quantum electrodynamics in strong electric fields: the ground-state Lamb shift in hydrogenlike uranium

X-ray spectra following radiative recombination of free electrons with bare uranium ions (U92+) were measured at the electron cooler of the ESR storage ring. The most intense lines observed in the spectra can be attributed to the characteristic Lyman ground-state transitions and to the recombination of free electrons into the K shell of the ions. Our experiment was carried out by utilizing the deceleration technique which leads to a considerable reduction of the uncertainties associated with Doppler corrections. This, in combination with the 0 degree observation geometry, allowed us to determine the ground-state Lamb shift in hydrogenlike uranium (U91+) from the observed x-ray lines with an accuracy of 1%. The present result is about 3 times more precise than the most accurate value available up to now and provides the most stringent test of bound-state quantum electrodynamics for one-electron systems in the strong-field regime.     

Rapid determination of fosetyl-aluminum residues in lettuce by liquid chromatography/electrospray tandem mass spectrometry

This paper describes a new method for the sensitive and selective determination of fosetyl-aluminum (Al) residues in vegetable samples. The method involves extraction with water by using a high-speed blender and subsequent injection of the 5-fold diluted extract into the liquid chromatograph. Fosetyl-Al is determined by liquid chromatography with electrospray tandem mass spectrometry after the addition of tetrabutylammonium acetate as the ion-pairing reagent. The method has been used to assay lettuce samples spiked at 2 and 0.2 mg/kg. Recoveries were satisfactory, with mean values of 98 and 106%, respectively, and relative standard deviations were < 10%. The limit of quantitation was 0.2 mg/kg, and the limit of detection was as low as 0.05 mg/kg. Matrix-matched calibration was used for quantitation, and the addition of an internal standard improved repeatability. The developed method allows the accurate and rapid determination of low levels of fosetyl-Al residues in lettuce with very little sample handling and good sensitivity; it was shown to be robust by the analysis of almost 100 samples.     

Synthesis and X-ray structure of 5′-methoxy-2,4,6-trimethyl-2′-nitrosobiphenyl

The synthesis and X-ray crystal structure of 5-methoxy-2,4,6-trimethyl-2-nitrosobiphenyl is reported. The compound (C₁₆H₁₇NO₂) is monoclinic, with a = 11.080(4), b = 16.899(6), c = 15.410(5) Å, = 108.329(5)°, and space group P2₁/n. There are two independent molecules within the crystal. In each of these molecules the two phenyl rings are mutually orthogonal, with interplanar dihedral angles of 85.09 and 89.43° respectively. The nitroso substituents are essentially coplanar with the phenyl ring, with torsional angles of only 3.5 and 2.2°, respectively, while the methoxy groups make angles of 5.2 and 10.0°, respectively, with the phenyl ring.     

Instrumental configurations for the determination of sub-micromolar concentrations of electroactive species with carbon,gold and platinum microdisk electrodes in static and flow-through cells

Microelectrodes should provide a greater analytical sensitivity than electrodes of conventional size. However, the detection of micromolar or lower concentrations with microdisk electrodes requires measurement of femtoamp currents, which is outside the range of most commercially available instrumentation. The novel use of a picoammeter or femto-ammeter as a current amplifier permits commercial instrumentation to be used with microdisk electrodes. Such instrumentation incorporating a picoammeter or femtoammeter is limited by the relatively slow rise time; this places restrictions on scan rates in all voltammetric techniques and on pulse widths in transient techniques such as differential pulse and square wave voltammetry. Because of the small currents, the ohmic (iR) drop is very small and polarization of the reference electrode is unimportant; thus a two-electrode format without a potentiostat can be used. Consequently, a microprocessor-based function generator and data storage system, in conjunction with a pico- or femto-ammeter, is satisfactory in providing inexpensive, versatile and very sensitive instrumentation for voltammetric detection with microdisk electrodes. Convenient methods for fabricating platinum, gold and carbon microdisk electrodes for use in stationary and flowing solution configurations are also presented.