Energy losses of slow protons in inhomogeneous electron gases

Summary The energy loss of a slow proton interacting with the electron gas surrounding an ionic core in a crystal lattice is estimated on the basis of local-density approximation for the electron gas and binary-collision approximation for proton-electron interactions. Comparison is made with the dielectric function approach to the same quantity and with experimental electronic-stopping cross-sections.

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Riassunto La perdita di energia di un protone lento interagente con il gas di elettroni che circonda un nucleo atomico in un reticolo cristallino si calcola in base all'approssimazione di densità locale per il gas elettronico inomogeneo e all'approssimazione di collisione binaria per l'interazione fra protone ed elettroni. Si confrontano i risultati con quelli ottenuti dal metodo della funzione dielettrica e con le sezioni d'urto sperimentali di frenamento electtronico.

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Резюме Оцениваются энертетичекие потери медленньых, вэаимодействующих с электронньим гаэом, окружающем ионный остов в кристаллической решетке, используя приближение локальной плотности для электронного газа и приближение бинарных соударений для прптон-электронных взаимодействий. Проводится сравнение с результатами, полученными с помощью циэлектричецкой функции, и с экспериенталными поперечными сечениями электронного торможения.

     

Determination of aflatoxins B1, G1, B2 and G2 in medicinal herbs by liquid chromatography-tandem mass spectrometry

An easy method for the determination of aflatoxins B1, G1, B2 and G2 in Rhammus purshiana by LC coupled to mass spectrometry has been developed. Aflatoxins were extracted with a mixture of methanol and water and then it was purified by solid-phase clean-up using a polymeric sorbent, not described previously, for the determination of these toxins. The eluted extract was injected into the chromatographic system using a reversed-phase C18 short column with an isocratic mobile phase composed of methanol-water (30:70). A single-quadruple mass spectrometry using an electrospray ionization source operating in the positive ion mode was used to detect aflatoxins due to derivatization presenting several disadvantages. Recoveries of the full analytical procedure were 110% for aflatoxin B1, 89% for aflatoxin B2, 81% for aflatoxin G1 and 77% for aflatoxin G2. Detection limit (S/N = 3) was 10 ng and quantification limit (S/N = 10) was 25 ng, calculated as amount in medicinal herb.     

Determination of chlorinated toluenes in raw and treated water samples from the Llobregat river by closed loop stripping analysis and gas chromatography-mass spectrometry detection

A study of the occurrence of chlorinated toluenes in Llobregat river (NE Spain) has been carried out. These compounds are currently being used in local textile industries as dye carriers and have replaced the common trichlorobenzene mixtures. Closed loop stripping analysis (CLSA), routinely used to monitor the quality of river water for a broad range of volatile compounds, has been employed as an analytical tool to determine them at ng/L levels in wastewater and textile industry effluents and also in raw and treated water from two drinking water treatment plants situated in the river course. The CLSA extracts were analyzed by HRGC/MS. Ring halogenated dichloro- and, to a lesser extent, mono- and trichlorotoluenes have been identified. These compounds have not been reported to our knowledge as common water pollutants.     

Detection in urine of efaproxiral (RSR13), a potential doping agent, by a routine screening procedure based on methylation followed by gas chromatography/mass spectrometry

Efaproxiral (also known as RSR13) is a synthetic allosteric modifier of hemoglobin. The ability to increase maximal muscle oxygen uptake makes RSR13 a potential performance-enhancing agent for athletes and, therefore, a new agent to be taken into account by the antidoping control laboratories. In this work, a new method for the detection of efaproxiral in urine by gas chromatography/mass spectrometry is described.     

Microanalysis of Hydrogen, Boron and Fluorine in Vesuvianite by Means of SIMS, EPMA and FTIR

Vesuvianite, a complex sorosilicate, often contains variable (from trace-to-minor-element) amounts of H, B and F. We describe a microanalytical study of H, B and F in vesuvianite by means of Electron Probe Microanalysis (EPMA), Secondary Ion Mass Spectrometry (SIMS), and single-crystal Fourier-Transform InfraRed (FTIR) spectroscopy. Most crystals investigated are B- (up to 3.67 wt% B₂O₃) and F-rich (up to 2.38 wt%); H₂O ranges from 0.243 to 0.665 wt%. The H data obtained by SIMS allowed us to calibrate the quantitative analysis of H₂O by FTIR spectroscopy. The resulting molar absorption coefficient (ɛ _i = 100 000 ± 2000 L · mol⁻¹ · cm⁻²) is in excellent agreement with working curves available from the literature. Moreover, the SIMS data allowed us to obtain the calibration curve to estimate the B₂O₃ content on the basis on the FTIR absorbance: a _i = 34000 ± 1400 · B₂O₃ (wt%).     

Bromine,arsenic, cadmium,and lead in several key food groups: an assessment of relative risk

ABSTRACT

This study endeavoured to provide an overview of the bromine, Br, arsenic (As, a metalloid) and metal (cadmium, Cd, and lead, Pb) relative risk associated with the consumption of relevant food groups (lean fish, fatty fish, bivalves, cephalopods, fresh fruit, dried fruit, and green vegetables) in Portugal. Though As, Cd, and Pb have been frequently studied, a comprehensive overview applying the same state-of-the-art methodology to a wide array of foods is missing. Besides, there is a large deficit of content information and risk assessment studies on Br. Thus, it is important to apply a mathematically realistic and innovative methodology (extreme value theory) to recent and accurate databases for the aforementioned food groups and elements.

Best fits to Br, As (total), Cd, and Pb concentrations were attained through different functions, ranging from the normal distribution to the Weibull distribution. A semi-probabilistic risk assessment approach on the basis of four alternative scenarios (one monthly meal; one weekly meal; three weekly meals; one daily meal) showed low relative risk regarding Br and Pb in the selected food groups, including bivalves, which contained the highest Br and Pb contents. With respect to total As, high relative risk values were calculated for seafood, but it should be emphasized that this As is overwhelmingly organic, thus presenting low risk. For Cd, substantial relative risk associated with bivalves’ and cephalopods’ consumption, particularly with one or more weekly meal(s), was found. However, the current study enables us to compare between the relative risk of the studied food groups and scenarios, and other studies encompassing the whole diet and following long-term dietary patterns are needed for the assessment of absolute risk.