In recent years, the classical Soxhlet extraction of PAHs and PCBs from matrices such as soil, sediments, sludges and related matrices has been substituted by faster and less-solvent-consuming automated techniques. This paper describes the performance characteristics of fluidized-bed extraction (FBE), which has been compared to other approaches and been optimized using a quality control material.SI-traceable reference materials from the European Commission have been used to validate the developed method and establish an analytical protocol. Good correlations with Soxhlet extraction were observed and certified values of the CRMs used, could be confirmed in all cases. 相似文献
The neutron capture gamma-ray spectroscopy facility assembled at the Institute of Radiochemistry, KfK (for analytical purposes) using a252Cf neutron source with a strength of 6·107 n/s, has been used to check its applicability and sensitivity for quantitative analyses of ores. The analysis of Sm, Cd and Mn in phosphate and monazite rock samples has been carried out. The results from this study show a variation of about 25% from the values determined by RNAA method. This discrepancy could be mainly due to the low signal-to-background ratio observed which is caused by (i) scattering of the source gammarays by the target, and (ii) interference from the 2223.1 keV neutron capture hydrogen gamma-rays produced by the moderated materials and from their compton scattering in the detector. To overcome these difficulties we suggest to introduce a 2.5 cm thick polyethylene sheet between the detector6Li-cap shielding and the target as well as to increase the detection solid angle. Also the strength of the252Cf neutron source should be increased by an order of magnitude and the neutron beam should be collimated to obtain the optimal thermal neutron flux with a low level of252Cf gamma-rays. This can be achieved by setting up between the neutron source and the target a conical polyethylene collimator with a thickness of 10 cm containing a 1 cm thick lead sheet. 相似文献
This study aims to investigate the distribution of Na, K, Rb and Cs in human brains (5 individuals, 12 brain parts, mean age: 75 years). Distribution of the trace metals between lipid fraction and brain tissue was investigated in solvent extraction experiments. Determinations were carried out by instrumental neutron activation analysis. The present results show a rather non-homogeneous distribution for Na and a relatively uniform distribution for K, Rb and Cs. The mean concentrations found are 7440µgNag–1 dry weight, 12800µgKg–1, 14µgRbg–1 and 50ngCsg–1. A highly significant positive correlation was found between Rb and Cs. Solvent extraction experiments showed that 19% of Rb and 26% of Cs of the total content is located in lipid fraction. 相似文献
Summary. An efficient synthesis of 2-fluoro-3-(trifluoromethyl)furans was developed. Keystep of the reaction sequence is a [4 + 1]
cycloaddition reaction of tin(II)chloride to 4,4-bis(trifluoromethyl)-1-oxabuta-1,3-dienes. At elevated temperatures the tin
heterocycles are transformed into 1-aryl-4,4-difluoro-3-(trifluoromethyl)but-3-en-1-ones which on treatment with sodium hydride
in dry DMF give 2-fluoro-3-(trifluoromethyl)furans. The single fluorine bound to C-(2) can be readily replaced by various N-, O-, S-,
and C-nucleophiles and dinucleophiles. 相似文献
Electromagnetically induced transparency (EIT) resonances are investigated with the 85Rb D1 line (795 nm) in strong magnetic fields (up to 2 kG) with three different types of spectroscopic vapor cells: the nano-cell with a thickness along the direction of laser light L ≈ 795 nm, the micro-cell with L = 30 μm with the addition of a neon buffer gas, and the centimeter-long glass cell. These cells allowed us to observe systematic changes of the EIT spectra when the increasing magnetic field systematically decoupled the total atomic electron and nuclear angular moments (the Paschen-Back/Back-Goudsmit effects). The observations agree well with a theoretical model. The advantages and disadvantages of a particular type of cell are discussed along with the possible practical applications. 相似文献
Summary. The single fluorine atom of 2-fluoro-3-trifluoromethylfurans and -thiophenes can be readily replaced by various nucleophiles.
Depending on the substituent pattern, certain products obtained upon nucleophilic substitution with benzyl alcohols are susceptible
to [1,3]- and [1,5]-benzyl group migrations under very mild conditions. Therefore, these rearrangements can be integrated
into domino reactions.
Received March 9, 2001. Accepted April 2, 2001 相似文献
Novel chitosan (CHS) and cellulose sulfates (CSs) are studied regarding their mitogenic activity and their protective effect against proteolytic digestion of FGF‐2. An intermediate degree of sulfation (DSS) and lower concentration of CHS have superior effect on 3T3 cell growth while the mitogenic activity of CS increases with DSS and concentration. Experiments with trypsin as model proteinase show that protection of FGF‐2 from proteolytic digestion depends on DSS and the concentration of derivatives in the same manner as cell growth. Studies on stability of FGF‐2 added to cultures of 3T3 cells show that the FGF‐2 concentration remains higher in the presence of derivatives. Results indicate that the mitogenic activity of CHS and CS is due to protection of FGF‐2 from proteolytic cleavage.