Arsenic determination in marine sediment using ultrasound for sample preparation.

This work deals with As determination in marine sediment using ultrasound for sample preparation. It is shown that As can be quantitatively extracted from marine sediment using 20% (v/v) HCl and sonication. The slurry is centrifuged and the analyte is determined in the supernatant by hydride generation atomic absorption spectrometry (HG AAS). A flow injection (FI) system is employed for hydride generation, with 0.5% (m/v) NaBH(4) used as reducdant and a 20% (v/v) HCl used as sample carrier. The limit of quantification is 1.6 microg g(-1) of As, which is based on 800 microl of sample solution and 0.200 g of sample mass in a volume of 50 mL. Certified and non certified marine sediment samples were analyzed; the results were in accordance with the certified or reference values. Speciation analysis by HPLC-ICP-MS showed that As(V) is the only detectable As species present in the supernatant of the centrifuged sample.     

Dosimetric investigations of laser-induced phase transition of MX1-cell membranes by use of quantum dots

It is well known that laser scattered-light applicators when applied for laser-induced tumor therapy allow the precise thermal destruction of metastases. Using laser radiation in the NIR spectral range (usually, Nd:YAG laser systems λ = 1064 nm), a penetration depth of 5–10 cm (1/e is the decrease in radiation intensity) is achieved in biological tissues. The major tissue-optical parameters, i.e., absorption coefficient μ_a, scattering coefficient μ_s, and the anisotropy factor g, show biological tissues to be strongly scattering media which have a so-called optical window in the NIR. As a consequence, the therapeutic laser radiation is scattered and absorbed at a deeper level, leading to a virtual enlargement of the laser applicator. The thermal sclerotization and the thermal cell damage originate within the absorbing volume of the laser radiation and spread outward by thermal diffusion. There are three dosimetrically relevant zones of thermal and biological damage: (1) a zone of thermal coagulation; (2) a threshold of partial necrosis (destruction of all metabolic processes in the cell is the maintenance of essential parts of the cytoskeleton and the plasma membrane); this is characterized by a specific temperature range, the so-called phase transition, which refers to the transition from the gel phase of the biomembrane to the fluid phase; the determination of this temperature zone is an integral part of the following experimental investigations on MX1 cells; (3) an external zone of thermal effects made up of partial and multiple damage with a statistical chance of survival. This paper describes the investigations on heat stress in cancer cells to verify the maximum phase transition of the outer MX1 cell membranes and the related results. For this purpose, a novel method of quantum dot fluorescence dosimetry was developed. The evaluation of the measured laser-induced fluorescences yields a first approximation of the determination of the phase transition on MX1 cells.     

A new approach for fluorine determination by solid sampling graphite furnace molecular absorption spectrometry

This work deals with the determination of fluorine by solid sampling graphite furnace molecular absorption spectrometry. The molecular absorbance of aluminum monofluoride (AlF), which is produced in the vapor phase in the presence of Al³⁺, is measured at 227.5 nm, a non-resonant platinum line. A conventional graphite furnace program has been used with pyrolysis and vaporization temperatures of 800 and 2300 °C, respectively. Solutions of Ba²⁺ and Al³⁺ have been used to avoid fluorine losses during the pyrolysis stage and to produce AlF in the vaporization stage, respectively. Certified coal and alumina samples were analyzed using aqueous standards for calibration. The agreement between the found concentration and the certified value, or the value obtained by another method ranged from 92 to 105%, with a relative standard deviation less than 8.5%. The limit of detection and the characteristic mass was 0.17 μg g^− 1 and 205 pg, respectively.     

Determination of trace elements in biological materials using tetramethylammonium hydroxide for sample preparation

A method to prepare milk powder, bovine liver and bovine muscle samples for analysis by electrothermal atomic absorption spectrometry (ETAAS) is proposed. Samples are mixed with a small amount of tetramethylammonium hydroxide (TMAH) and a stable and homogeneous slurry is produced in ca. 2 h with heating at 60–70 °C. After such sample preparation and dilution with water, trace elements are determined in certified reference materials. Pyrolysis and atomisation temperatures are optimised for each element, and several modifiers are investigated. External calibration is used for every analyte. Limits of detection (LODs), precision and accuracy are reported for Cd, Pb, Ni, Cr, Cu and Ag and compared with those obtained after conventional acid digestion. The main advantages of the proposed method are the simplicity of sample preparation and the longer lifetime of the graphite tube.     

Determination of copper in medicinal plants used as dietary supplements by atomic absorption spectrometry with direct flame solid analysis

An alternative device for the direct solid analysis (DSA) for copper determination by flame atomic absorption spectrometry (FAAS) is proposed. Copper was directly determined in commercial medicinal plants used as dietary supplements. The determination of copper in solid samples by DSA–FAAS was made by using a conventional air–acetylene flame. Between 0.05 and 1.5 mg of each test, sample was weighed directly into a small polyethylene vial connected to the device used for solid introduction into the flame. Test samples were introduced into the flame as a dry aerosol using a T-quartz cell set between the burner and the optical path. The T-quartz cell has a slit in the superior part by which the solid aerosol passes to the flame. A transient signal, evaluated as integrated absorbance, is produced and it is totally integrated in 2 s. Background signals always presented absorbance values less than 0.1. It was found a characteristic mass of 0.8 ng Cu and absolute limit of detection of 1.2 ng (3 s), or 1.2 μg g⁻¹ if a sample mass of 1 mg was used. Optimized conditions for air flow rate, flame stoichiometry, and so on were established as well. No excessive grinding of the samples was needed and samples with particle of size less than 80 μm were used throughout. No statistical difference between the results from the proposed system and those obtained by sample digestion and determination by conventional FAAS was observed. With the proposed procedure, more than 50 test samples can be analyzed in 1 h and it can be easily adapted to conventional spectrometers for FAAS.     

Comparison of theory and experiment for excited singlet states of the H2 molecule

This paper presents a survey of published and unpublished ab initio calculations of the vibrational structures of the ten lowest electronic singlet states of the hydrogen molecule up to the H(n = 1) + H(n = 2) dissociation limit. The data are based on adiabatic potential functions (clamped-nuclei electronic energies and nuclear-mass-dependent diagonal corrections). Nonadiabatic coupling has been treated ab initio within the five states. of ¹Λ symmetry (X,EF, GK, HH?) and ¹Σ I.¹Π_g. The accuracies of the theoretical energies are determined by comparisons with experimental data for H₂, HD, and D₂. The level shifts and predissociation probabilities of the excited ¹Σ states, generated by nonadiabatic coupling with the discrete and continuous vibrational structure of the ground state, and radiative properties have also been calculated.     

Determination of Mo, U and B in waters by electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the determination of Mo, U and B in waters by inductively coupled plasma mass spectrometry, using an electrothermal vaporizer for sample introduction, is described. For Mo and U, NH(4)F was chosen as modifier and for B, synthetic sea water plus mannitol were used. The modifier effect was verified and the optimized pyrolysis and vaporization temperatures were obtained from pyrolysis and vaporization curves, together with the transient signals of the analytes. The masses of the modifiers added to the tube were also optimized. The detection limits were 0.018 or 0.30 ng ml(-1) for Mo, 0.03 ng ml(-1) for U and 0.68 ng ml(-1) for B. The analytes were determined in certified waters and the obtained results agree with the certified or recommended values or, in the case of B in sea waters, with the values obtained by other methods. Uranium could not be measured in the sea water samples due to strong memory effect.     

Potentiometric determination of fluoride in geological and biological samples following pyrohydrolytic decomposition

A method for the determination of fluoride in coal, coal fly ash, phosphate rock, limestone, mineral clay, fossilised materials, oyster tissue and vegetation using pyrohydrolysis for sample decomposition is proposed. A specific apparatus was constructed and the influence of vanadium pentoxide (V₂O₅) as a catalyst for the pyrohydrolysis reaction was investigated. It was verified that V₂O₅ does not influence the release of fluoride from the vegetation, oyster tissue, coal and coal fly ash matrices analysed. However, the catalyst was necessary for the phosphate rock, fossil bone, mineral clay and limestone samples. Certified and noncertified samples were analysed using an ion selective electrode (ISE) for the analyte detection. Precise (relative standard deviation—R.S.D.<7%) and accurate (recovery in accordance to certified values) results were obtained. The limit of quantification (LOQ) of the method was 5.0 μg g⁻¹ of fluoride using 20 mg of sample and a final dilution to 10 ml. The sample frequency was five samples per hour.     

Rho(0) meson production in the pp-->pppi(+)pi(-) reaction at 3.67 GeV/c

Total and differential cross sections for the exclusive reaction pp-->pp rho observed via the pi(+)pi(-) decay channel have been measured at p(beam)=3.67 GeV/c. The observed total meson production cross section is determined to be (23.4+/-0.8+/-8) mu b and is significantly lower than typical cross sections used in model calculations for heavy-ion collisions. The differential cross sections measured indicate a strong anisotropy (approximately cos(theta(CM)(rho)) in the rho(0) meson production.     

Gaps between integers with the same prime factors

We give numerical and theoretical evidence in support of the conjecture of Dressler that between any two positive integers having the same prime factors there is a prime. In particular, it is shown that the abc conjecture implies that the gap between two consecutive such numbers is , and it is shown that this lower bound is best possible. Dressler's conjecture is verified for values of and up to .