Factors influencing enantiomeric fractions of hexabromocyclododecane measured using liquid chromatography/tandem mass spectrometry

Hexabromocyclododecane (HBCD), the most heavily produced of the cycloaliphatic brominated flame retardants (BFRs), is a mixture of three predominant diastereomers (alpha-, beta-, and gamma-HBCD), each with a corresponding pair of enantiomers. We have investigated the liquid chromatography/mass spectrometry (LC/MS) behaviour of the HBCD enantiomers, and demonstrated that enantiomeric fractions (EFs) calculated using data uncorrected for instrument and/or matrix effects can result in potentially inaccurate EF values. However, use of labelled surrogates effectively corrects for these effects. Experiments with racemic HBCD standards indicate that chromatographic factors, including mobile phase composition and column bleed from chiral stationary phases, may be contributors to variations in the mass spectrometric response of the HBCD enantiomers.     

HPTLC-Bestimmung von Paracetamol im Serum

Ohne Zusammenfassung

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Determination of paracetamol in serum by HPTLC

     

Les effets causes par les dimensions de la source dans les systemes optiques eclaires en lumiere spatialement incoherente

It has been shown recently that in order for an incoherent optical system to be linear and space invariant, the image of the source at the filter plane must be larger than the filter aperture. We show in this paper that the source image must be larger than the filter by an amount equal to twice the highest spatial frequency of the object, the frequency being measured in the filter plane.     

Estimators of the regression parameters of the zeta distribution

The zeta distribution with regression parameters has been rarely used in statistics because of the difficulty of estimating the parameters by traditional maximum likelihood. We propose an alternative method for estimating the parameters based on an iteratively reweighted least-squares algorithm. The quadratic distance estimator (QDE) obtained is consistent, asymptotically unbiased and normally distributed; the estimate can also serve as the initial value required by an algorithm to maximize the likelihood function. We illustrate the method with a numerical example from the insurance literature; we compare the values of the estimates obtained by the quadratic distance and maximum likelihood methods and their approximate variance–covariance matrix. Finally, we calculate the bias, variance and the asymptotic efficiency of the QDE compared to the maximum likelihood estimator (MLE) for some values of the parameters.     

Statistical properties of speckle recorded on film

The statistical properties of speckle recorded on photographic film are studied theoretically and experimentally. When saturation and threshold effects are negligible and the gamma is equal to one, the probability distribution function of spatially integrated film transmittance has the form of a double exponential. Experimental results confirm that under those conditions, the density fluctuations caused by the speckle are independent of the signal.     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

The solution to the phase retrieval problem using the sampling theorem

A phase reconstruction method based on the two-dimensional sampling theorem is applied to the case when only the modulus of the Fourier transform and the support of the object are known. The convengence of the algorithm is analysed for different intermediate sampling grids and for different initial values.     

Synthetic self-propelled nanorotors

Self-powered completely synthetic nanorotors have been prepared from barcoded gold-nickel nanorods having the gold end anchored to the surface of a silicon wafer; constant velocity circular movements are observed when hydrogen peroxide fuel is catalytically decomposed to oxygen at the unattached nickel end of the nanorod.