Effects of ammonium fluoride on the decomposition of geochemical samples as fluorinating agent and its analytical application.
In this work, the effects of ammonium fluoride on the decomposition of geochemical samples were investigated by analyzing some certified reference materials (CRM). The major and minor elements were detected by inductively coupled plasma optical emission spectrometry (ICP-OES), while trace and ultra-trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Decomposition time, temperature and the amount of ammonium fluoride were studied in detail. In the process of sample decomposition, on one hand, ammonium fluoride was used as the fluorinating agent because ammonium fluoride can be dissociated under acid medium to yield fluoride ions to attack silicon compound effectively. On the other hand, ammonium fluoride was used as a latent solvent since ammonium salt may dissolve insoluble fluorine compounds. The removal of insoluble fluorine compounds decreased the memory effect on digestion vessels caused by fluoride coprecipitation. By testing CRMs and many real samples, it was found that trace and ultra-trace elements could be digested using ammonium fluoride instead of hydrofluoric acid and the dissolution ratios of major and minor elements, for example Al, Ca, Mg, Fe, Na and K, improved noticeably. Moreover, the use of ammonium fluoride instead of hydrofluoric acid contributes to a greener environment and safer for operators.
Development and application of an analysis method for the determination of rare earth elements in silicate-rich samples by Na2O2 sintering and ICP–MS analysis
The performance of a fast and simple analytical procedure for rare earth elements (REEs) quantification from secondary sources was investigated in the present work. Seven silicate-rich certified reference materials (CRMs) in the form of Andesite (JA-1), Basalt (JB-3), Rhyolite (JR-1, JR-2), Granite (JG-2), Granodiorite (JG-3), and Till (TILL-1), were used for the optimization and characterization of the analysis method. The optimized method was used in the analysis of nine mining wastes selected within the ENVIREE project, under the ERA-MIN Program of the 7th Framework, having as the main aim to ensure a policy securing long-term access of REEs secondary sources at reasonable costs. For silicate-rich samples efficient solid dissolution involves sintering with Na2O2 at 460 °C and a sample to oxidizing reagent ratio of 1:6.5. Inductively coupled plasma–mass spectrometry (ICP–MS) was used in the quantification of the REEs with aerosol dilution of samples applied to minimize the salt effect on the plasma and interface regions. The work performed in the present study clearly shows that accurate reports on the REE concentrations from geological matrices also involves as mandatory the estimation of the overall uncertainty from various sources (sample preparation or analyte measurements). In the analysis of geological samples, the proposed analysis method has on average 23% of the overall uncertainty explained by the sample preparation and 77% accounted by the analysis steps. Moreover, the method described by effective, cheap, robust and safe attributes, can be recommended as an accessible alternative to the HF wet digestion method. Although from all the investigated tailings samples, only those from Sweden and Czech Republic can be regarded as potential secondary sources for REEs, investigation of other resources with interest at European level might bring a great benefit in the general attempt to develop an economically viable method for the production of rare earth elements.
Inhibitors of monoamine oxidase. Influence of methyl substitution on the inhibitory activity of beta-carbolines.
A number of tetrahydro and aromatic β -carbolines, mostly with a methyl substituent at various positions, were synthesized and their in vitro inhibitory activities on monoamine oxidase evaluated. Substitution of a methyl group at the N-9 nitrogen of tetrahydro- β -carboline gave a potent competitive inhibitor of the enzyme. Methyl groups at C-1 of both tetrahydro and aromatic β -carbolines generally reduced the potency, whereas introduction of a methyl group at the N-2 nitrogen of tetrahydro- β -carboline gave a compound of equal activity.