Application of a mercuric iodide detector for the exploration and exploitation of niobium deposits in remote areas

The comparison of an ambient temperature mercuric iodide spectrometer (HgI₂) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI₂ spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the Nb_K peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela.     

Determination of cadmium in urine by platform ET-AAS independent of matrix composition

Summary The optimization of the heating conditions, absorbance profiles, the influence of different matrix composition and the effect of delivering different volumes of urine samples were examined in order to evaluate the use of simple aqueous standards for the determination of cadmium in urine samples, using atomic absorption spectrometry with electrothermal atomization and the L'vov platform. Three reference materials were analysed for cadmium by the proposed method. The results indicate that a direct and accurate determination of urine cadmium is possible by using simple aqueous calibration standards, independently of the composition of the urine matrix.     

Application of the slurry technique to biological materials: a survey of literature

Summary The literature on the application of the slurry technique to biological materials is reviewed. It is obvious from the various applications that the most frequently employed atomization method for slurry analysis in biological materials is electrothermal atomization using either graphite tube or platform atomizers. The slurry technique is particularly useful when certified reference materials are not available and when the standard addition method is to be avoided. The literature survey revealed that this technique compares favourably with other methods for the determination of trace metals in biological materials.     

Lichens as biomonitors for the determination of polycyclic aromatic hydrocarbons (PAHs) in Caracas Valley,Venezuela

Biomonitoring of PAH air pollution using lichens was carried out. Sixteen PAHs were studied in 11 locations along the valley of Caracas (Venezuela). The results of this work indicate that 14 of the 16 analysed PAHs were highly accumulated into the lichen thalli of Pyxine coralligera Malme. PAH levels in the samples revealed that the several volatile PAHs (naphthalene, acenaphtylene, acenaphtene, and fluoranthene) have the highest levels in the majority of the studied locations. The fluoranthene/pyrene and phenantrene/antracene ratios suggested that the major sources of PAHs are anthropogenic, mainly associated with gasoline and diesel combustion (pyrolytic) and unburnt oil derivates (petrogenic). The total PAH concentrations obtained in the present study were in the range of 0.24 to 9.08?µg/g, similar to those reported by other works in European and Asian cities.     

Molecular structure of trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2

The title compound crystallizes in the orthorhombic space group Pnma, with a = 7.9209(5), b = 9.818(1), c = 16.867(2) Å, and Z = 4. The structure was solved employing 1864 independent x-ray reflections with I>2(I) by Patterson and difference Fourier techniques and refined by full-matrix least-squares to R = 0.036. The trans-[CO(NH₃)₄(NH₂CH₃)Cl](ClO₄)₂ molecule is on a crystallographic mirror plane. The cobalt ion is in an elongated octahedral coordination with four equatorial ammonia ligands [average Co–N distance equal to 1.966(2) Å], an axial methylamine [Co–N=1.965(3)Å], and an axial chlorine ion [Co–Cl=2.2771(9)Å]. Kinetic steric effects of the complex are interpreted in terms of structural results.     

Determination of the threshold odor concentration of main odorants in essential oils using gas chromatography-olfactometry incremental dilution technique

In dual-flow counter-current chromatography (DF-CCC), the two immiscible liquids are flowing in opposite directions in the coil. The method allows for the continuous separation of two solutes. In this study a numerical model was developed to allow for the detailed investigation of flow in such columns. The mesh model of the presented DF spiral column was developed in line with an existing experimental model. The paper presents results during the early filling stages for different rotation directions. These clearly illustrate the performance of the developed model by (1) confirming the importance of flowing the lighter phase from tail to head and the heavier phase from head to tail and (2) by visualising mixing waves and the recognised back and forth "swish-swash" motion as present in CCC in that operating mode.     

Application of a fractional factorial design for the determination of cadmium by ETA-AAS in different atomization systems

A multivariate study was applied to the investigation of the variables affecting the cadmium sensitivity in a graphite furnace, with and without platform atomization or matrix modifier. The results indicated that, depending on the atomization system used, the factors studied (drying, ashing, atomization, calibration curve) exert an influence on the analysis. The interactions between the factors were also analyzed.     

Simultaneous determination of nickel,iron, and copper in margarine by inductively coupled plasma-atomic emission spectroscopy after sample emulsification

Nickel, iron, and copper were determined in margarine samples by using emulsification followed by inductively coupled plasma-atomic emission spectroscopy. Sample treatment and instrumental conditions were optimized, and the results were compared with those obtained by a pseudodigestion method in order to evaluate the compatibility of both methodologies. The optimum amount of margarine in the emulsion was 35% when the surfactant Tween 80 was added as the emulsifier. Copper was below the detection limits of both methodologies, i.e., digestion and emulsion; iron and nickel concentrations found by both methodologies were similar. The detection limits of the emulsion method were 0.002, 0.015, and 0.092 mg/kg for copper, iron, and nickel, respectively. A benefit of the emulsion method is that laborious and lengthy sample digestion procedures are avoided. In addition, accurate and precise results are obtained. Recoveries with the emulsion method ranged from 101 to 104%, with relative standard deviations of < or = 6%.     

On the splitting of ν(OH) k = 0 phonons and band-width in hydrogen bonded organic solids: α-naphthol

α-naphthol crystallizes with the same type of hydrogen bonded chain like planar zig-zag structure as other XH…X systems (X = F, Cl, Br, and sometimes O). The intramolecular k = 0 splitting for ν(OH) motions of α-naphthol has been clearly observed in the infrared spectrum with polarized light on iso-oriented small single crystals. It is found that the observed intramolecular ν(XH) splitting or the corresponding f_XH/XH nearest neighbour quadratic force constants across the hydrogen bond can be correlated with the electronegativity of the X atom.