MS-Xα calculations on boron trihalides and comparison with their photoelectron spectra

The multiple-scattering Xα model has been applied to the sequence of boron trihalides BX₃ where X = F.C1. Br, and I. Transition state calculations show good agreement with the experimental ionization potentials measured by photoelectron spectra.     

Flow Rate Profiler: an instrument to measure blood velocity profiles

In this paper we present Flow Rate Profiler (FRP), an instrument for measuring the blood velocity by means of ultrasound-based techniques. The velocity is directly related to the shear rate, which is in turn proportional to the shear stress, a parameter expressing the pressure exerted by the blood on the vessel walls. The knowledge of this value is important in medicine to establish the state of the vessels, directly related to vascular diseases. FRP provides a non-invasive measure of the blood velocity by exploiting the red corpuscles property of diffusing ultrasound waves: in practice blood velocity is determined by a cross-correlation technique, which analyses the time shift between correlated subsequent echo waves, instead of frequency shift characteristic of the Doppler technique. The acquired data are then processed on a personal computer by means of mathematical techniques based on the evaluation of the correlation function, giving a reconstructed velocity profile and showing a good adherence with experimental data, since the average error is nearly the 10%. The reconstructed profile is displayed to the operator, who can follow the vessel status in real time. A few comparisons between the reconstructed and the experimental profiles are also presented, together with a study on a small set of patients suffering from artery hypertension.     

Some properties of the zeros of orthogonal polynomials

Summary Some inequalities involving the zeros of the classical orthogonal polynomials are established; these are applied to show that certain Riemann sums have monotone convergence.     

Multi-residue determination of non-steroidal anti-inflammatory drug residues in animal serum and plasma by HPLC and photo-diode array detection

The European Union regulated the use of non-steroidal anti-inflammatory drugs (NSAIDs) in animal production and set the official analytical controls to detect their residues in plasma, serum, and milk within the frame of national monitoring programs in each member state. In this work, a multi-residue reversed-phase high-performance liquid chromatography with diode array detector (DAD) method is described for the simultaneous determination of 13 NSAIDs in serum and plasma of farm animals. Chromatographic separation by a C12 stationary phase column with a linear gradient is able to resolve all the compounds considered: salicylic acid, ketoprofen, flurbiprofen, phenylbutazone and its metabolite (oxyphenbutazone), carprofen, ibuprofen, naproxen, niflumic acid, suxibutazone, diclofenac, mefenamic acid, and tolfenamic acid. These compounds are chosen as the most representative of the different NSAID chemical sub-classes. The DAD analysis allows the confirmation of all drugs on the basis of their own UV-vis spectrum, according to the requirements of the European Council Decision 2002/657/EC. Moreover, the method is in-house validated, evaluating mean recoveries, specificity, repeatability, and within-laboratory reproducibility as the performance parameters required by the Decision. The results of this study indicate the method is specific and repeatable, with the mean percentage recoveries of the drugs ranging between 72.5% and 104.5%. Only salicylic acid has poor recovery, with results ranging between 36.3% and 54.9%.     

Influence of the substrate electronic structure on metallic quantum well state dispersions in ultrathin metal films

We have studied ultrathin Cu films grown on three related ferromagnetic (FM) layers to clarify the role of the substrate in determining the two-dimensional dispersion of metallic quantum well (MQW) states in the overlayer. The dispersions with parallel momentum of Cu MQW states above the Fermi level E_F were measured in the Cu/fccFe/Cu(1 0 0) and Cu/fccCo/Cu(1 0 0) systems using inverse photoemission, and below E_F in the Cu/fccNi/Cu(1 0 0) system using angle resolved photoemission spectroscopy. This study focussed on the direction of the two-dimensional Brillouin zone. For states away from the projected band gaps of the FM layer, the identity of the FM layer (i.e., Fe or Co) has little influence on Cu MQW states and their dispersions closely resemble those of a free standing Cu film. In contrast, all three systems exhibit nondispersing MQW states when the Cu bands overlap the minority spin projected band gaps of the FM metal. A phase accumulation approach gives a very simple explanation of this behavior, showing that the flat dispersion occurs because the phase shift upon reflection from the FM layer has a strong energy dependence in the projected gap.     

Non-muffin-tin MS Xα total energies for H2, C2, N2 and CO

NMT (non-muffin-tin) MS Xα calculations for the ground state potential curves are reported for the molecules H₂, C₂, N₂, and CO. These calculations include corrections linear and second order in the NMT charge density and show great improvement over the MT (muffin-tin) curves. With these corrections, somewhat better agreement with experiment is also found. A comparison is made between tne Xα and the local spin density (LSD approximations for the H₂ and CO molecules.     

In-house validation of a liquid chromatography/electrospray tandem mass spectrometry method for confirmation of chloramphenicol residues in muscle according to Decision 2002/657/EC

In this work we present an in-house validation study for the confirmatory analysis of chloramphenicol (CAP) in muscle according to the Commission Decision 2002/657/EC requirements. CAP is extracted in acetonitrile and after liquid-liquid partitioning with n-hexane is identified and quantitatively determined by ion trap liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) analysis in the negative ion mode. CAP was identified using the precursor ion and at least two product ions, meeting the qualitative and quantitative criteria set by the European Commission in the Decision 2002/657/EC for confirmation of prohibited veterinary drug residues. We calculated mean drug recoveries, CCalpha and CCbeta of the method, and reported data on specificity, ruggedness and within-laboratory reproducibility. Finally, we point out and discuss some problems and questions arising from controversy about the application of Decision 2002/657/EC.     

Development of a new ultra-high-performance liquid chromatography–tandem mass spectrometry method for the determination of digoxin and digitoxin in plasma: Comparison with a clinical immunoassay

Cardiac glycosides digoxin and digitoxin are used in therapy for the treatment of congestive heart failure. Moreover, these compounds can be responsible for intoxication cases caused by fortuitous ingestion of leaves of Digitalis. Due to the narrow therapeutic range of these drugs, therapeutic drug monitoring is recommended in the clinical practice. In this context, immunoassays-based methods are generally employed but digoxin- and digitoxin-like compounds can interfere with the analysis. The aim of this study was to develop and validate an original UPLC–MS/MS method for the determination of digoxin and digitoxin in plasma. The method shows adequate sensitivity and selectivity with acceptable matrix effects and very good linearity, accuracy, precision, and recovery. A simple liquid–liquid extraction procedure was used for sample clean-up. The method was applied for the analysis of n = 220 plasma samples collected in two different clinical chemistry laboratories and previously tested by the same immunoassay. The statistical comparison showed a relevant negative bias of the UPLC–MS/MS method versus the immunoassay. These results are consistent with an immunoassay overestimation of digoxin plasmatic levels due to cross-reaction events with endogenous digoxin-like substances.     

Confirmatory identification of sixteen non-steroidal anti-inflammatory drug residues in raw milk by liquid chromatography coupled with ion trap mass spectrometry

The European Council Decision 2002/657/EC established that group B substances detected in foods must be identified and confirmed on the basis of their molecular structure. To this aim, we have developed a panel of methods for unambiguous determination of sixteen non-steroidal anti-inflammatory drugs (NSAIDs) in cattle and buffalo raw milk. A multi-residue reversed-phase high-performance liquid chromatography method with photodiode array detection is described for quantitative screening analysis. For confirmatory purposes, two multi-residue reversed-phase ion trap liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) methods were developed: the former to identify salicylic acid, naproxen, carprofen, flurbiprofen, ibuprofen, meclofenamic acid, niflumic acid, flunixin and its metabolite 5-hydroxyflunixin in the negative ion mode; the latter to identify ketoprofen, suxibutazone, diclofenac, mefenamic acid, tolfenamic acid, phenylbutazone and its metabolite oxyphenbutazone in the positive ion mode. These drugs are representative of different subclasses of NSAIDs not chemically related. The methods were in-house validated, evaluating specificity and calculating the mean recoveries, repeatability, within-laboratory reproducibility, and limits of quantification. For all the NSAIDs, apart from salicylic acid and 5-hydroxyflunixin, mean recoveries ranging between 69.0% and 96.7% were measured. The qualitative identification of all drugs was attained by their MS/MS spectra in the concentration range studied. Similarly, at 5 microg/kg all NSAIDs, apart from flurbiprofen, were unambiguously confirmed.