Limitations and perspectives in the determination of carbofuran with various liquid chromatography-mass spectrometry interfacing systems

Column liquid chromatography with mass spectrometric detection (LC-MS) has been widely accepted as the preferred technique for the identification and quantification of polar and thermally labile compounds at trace levels. Over the last decade many different types of LC-MS interfacing techniques have been used for the determination of carbamate pesticides and especially for the N-methylcarbamate carbofuran. This article addresses the difficulties encountered with the various types of LC-MS interface and discusses recent alternatives for the determination of carbofuran. With thermospray and particle beam interfaces the quantification of carbofuran is affected by both the ion source pressure and temperature, whereas quantification using the recently developed atmospheric pressure ionization interfaces, atmospheric pressure chemical ionization, electrospray, and ionspray, is less dependent on these parameters.     

Application of diode array detectors for solute identification in toxicological analysis

Summary The possibilities and limitation of automated solute identification via UV/VIS spectroscopy in HPLC are demonstrated and applications in toxicologic analysis are described. A standard isocratic system is used. The influence of various chromatographic parameters on retention time is shown. A retention time window of ±15% is required. In addition to retention time, derived spectral data are calculated (minima and maxima of derivatives, area counts under standardized spectral ranges, absorption at various wavelength) and used for positive solute identification. It is possible to identify solutes with a high degree of certainty in urine and plasma if their concentration is at least 10 ppm.     

Crystal structure of the ceramic superconductor BaPb0.75Bi0.25O3

The ceramic superconductor BaPb_0.75Bi_0.25O₃ is monoclinic atT<430 K with space groupI2/m. Lattice constants and the atomic coordinates result from 20 reflection groups (12<2<120°, =1.1267 Å) collected with a high resolution powder diffractometer using a synchrotron radiation source and a full neutron powder pattern (6<2<140, =1.909 Å). Synchrotron and neutron data were simtultaneously refined with SIMREF, a new profile refinement program, based on the Rietveld method. Group theoretical analysis of the distortion field leading from the ideal perovskite structure toI2/m exhibitsR ₄ ⁺ symmetry. A comparison is made with the corresponding distortions in nonsuperconducting BaBiO₃ where three different symmetry types are identified. The space groupI2/m found for BaPb_0.75Bi_0.25O₃ allows only one type of averaged (Pb/Bi)O₆ octahedron in the structure: this may support valence fluctuations and hence contribute to the mechanism of superconductivity in this particular compound.     

Observed difference between the probabilities of recoilless resonance absorptionf′ and reemissionf″ of gamma-quanta in single crystals of Na2[Fe(CN)5NO]·2 H2O

The recoilless absorption probability factor,f, and recoilless reemission,f, both measured on Na₂[Fe(CN)₅NO]·2 H₂O single crystals using the black filter technique, were found to be different. Unexpectedly, the results found weref>f. In the calculation off, selfabsorption in the scatterer, non-ideality of the black filter and the influence of non-resonant scattering processes have all been taken into account. By varying the scattering geometry for the incoming and outgoing -beam relative to the crystallographic axes only a change in the reemitted valuesf _a, f_b, f_c could be detected because of the long lifetime of the excited nucleus (10^–7 s) relative to the lattice vibration frequencies (10¹² Hz).     

Über die lokale Zetafunktion von Shimuravarietäten. Monodromiefiltration und verschwindende Zyklen in ungleicher Charakteristik

Ohne Zusammenfassung

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On the local zeta function of Shimura varieties. Monodromy filtration and vanishing cycles in unequal characteristic

     

The luminescence of Pr3+ in BaY4Si5O17

The cell constants of four new monoclinic compounds BaR₄X₅O₁₇ (R = Y, Gd; X = Si, Ge) are given. The luminescence of various RE activators in the silicates is reported. Pr³⁺-activated BaY₄Si₅O₁₇ shows efficient ultraviolet 5d → 4f emission and weak 4f → 4f emission (mainly red luminescence from the ¹D₂ level). The 5d → 4f emission is ascribed to Pr³⁺ on Y sites, the 4f → 4f emission to Pr³⁺ on Ba sites. Energy transfer from Pr³⁺ to Gd³⁺ has been observed. Gd³⁺ plays an intermediate role in the energy transfer from Pr³⁺ to Sm³⁺ and to Dy³⁺ in BaGd₄Si₅O₁₇. Upon activation with Tb³⁺ the silicates show characteristic green Tb³⁺ luminescence with a quantum efficiency of 75% for ultraviolet excitation.     

Matrix isolation infrared spectra of the complexes between methylacetate and water or hydrochloric acid

The hydrogen-bonded complexes between methylacetate (MeAc) and water or hydrochloric acid have been studied by infrared spectrometry in a low temperature Argon matrix. The ν_CO, ν_CC and ν_CC ional modes of MeAc show a splitting to the low and to the high frequency side of the free molecule. This suggests that water and HCl interact with the keto and ether oxygens. This conclusions is supported by the appearance of two main absorptions in the ν_HCl region. These results are discussed as a function of the gas-phase basicity of the two oxygen atoms, derived from the O(1s) core electron binding energies and from the ionization potentials.     

Determination of aminophenol isomers in water samples by extraction and thin-layer chromatography densitometry

A TLC densitometric method for the determination of the aminophenol isomers in water samples has been developed. The aminophenols are first extracted into chloroform-isoamylalcohol (1:2) mixture. The extracted aminophenols are separated on a TLC plate and visualized by spaying solution of 2,4,7-trintro-9-fluorenone in acetone. The colored spots are scanned for light absorption or reflection and the amount of each aminophenol is evaluated.     

Determination of mono-ortho substituted chlorobiphenyls by multidimensional gas chromatography and their contribution to TCDD equivalents

The mono-ortho chlorobiphenyls (CBs) 60, 74, 114, 123, 157, 167 and 189 were determined in Aroclor mixtures and aquatic organisms by multidimensional gas chromatography with electron capture detection (MDGC/ECD), using a combination of an Ultra 2 and an FFAP column. MDGC/ECD is recommended as the most suitable technique for direct determination of these CBs, without a liquid chromatographic (LC) pre-separation of mono-ortho CBs from the other CBs. Dependent, to some extent, on the stationary phase used, single-column determinations of these CBs easily yield too high results due to the presence of interferences. The contribution of the mono-ortho CBs studied to the total 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs) from CBs in fish is highly dependent on the toxic equivalency factors (TEFs) used and varies between 0.02 and 22%. This contribution is mainly due to CBs 74, 114, 157 and 167 which may easily be determined by taking three heart-cuts and combining them into one MDGC/ECD run. The analytical error is negligible compared with the huge uncertainty of the TEFs. A need for more precise TEFs is emphasized.