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排序方式: 共有173条查询结果,搜索用时 15 毫秒
1.
Tuomas Aitasalo Jorma Hls Hgne Jungner Jean-Claude Krupa Mika Lastusaari Janina Legendziewicz Janne Niittykoski 《Radiation measurements》2004,38(4-6):727-730
The UV excited and persistent luminescence properties as well as thermoluminescence (TL) of Eu2+ doped strontium aluminates, SrAl2O4:Eu2+ were studied at different temperatures. Two luminescence bands peaking at 445 and 520 nm were observed at 20 K but only the latter at 295 K. Both Sr-sites in the lattice are thus occupied by Eu2+ but at room temperature efficient energy transfer occurs between the two sites. The UV excited and persistent luminescence spectra were similar at 295 K but the excitation spectra were different. Thus the luminescent centre is the same in both phenomena but excitation processes are different. Two TL peaks were observed between 50 and 250 °C in the glow curve. Multiple traps were, however, observed by preheating and initial rise methods. With longer delay times only the high temperature TL peak was observed. The persistent luminescence is mainly due to slow fading of the low temperature TL peak but the step-wise feeding process from high temperature traps is also probable. 相似文献
2.
Backman Ulrika Jokiniemi Jorma K. Auvinen Ari Lehtinen Kari E.J. 《Journal of nanoparticle research》2002,4(4):325-335
We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size. 相似文献
3.
The purpose of this investigation is to develop a rapid and simple method for the assessment of organophosphorus pesticides in bovine muscle by using solid-phase extraction (SPE). After extraction with ethyl acetate (EtOAc) the homogenate is centrifuged and filtered through sodium sulfate. The fat is precipitated in methanol by cooling and the extract is diluted with water and passed through a SPE column (Isolute ENV+). After elution with EtOAc, evaporation, and redissolution, the sample is injected into a gas chromatographic (GC) capillary column DB-1701 and detected by a flame photometric detector. Recoveries from bovine muscle fortified with 12 pesticides between 4 and 65 microg/kg include three levels ranging between 59% and 109% for ten of them. The two most polar pesticides (metamidophos and acephate) are not successful. The relative standard deviations are between 1% and 10% for the ten pesticides. A simplex method is used to optimize the GC conditions. 相似文献
4.
S. Korhammer Rolf Herzig Peter Schramel Jorma Kumpulainen Bernd Markert Herbert Muntau Philippe Quevauviller 《Accreditation and quality assurance》2000,5(6):238-242
Cabbage is frequently used in environmental monitoring and food control, and, hence, cabbage reference materials (RMs) are
required for ensuring quality assurance. A cabbage RM was prepared in view of certification of specific elements from the
"black list" of high toxicological interest and nutritive importance. All tasks of the RM production (production of the plant
material, cutting and freeze-drying, determination of the residual water content, preparation of the RM, homogeneity testing,
stability testing, certification measurements) are described in detail.
Received: 12 November 1999 / Accepted: 29 January 2000 相似文献
5.
Summary Lead and cadmium contents of berries and vegetables of both domestic and imported origin were studied in samples collected from the Finnish food industry (berries) or from large wholesale markets (vegetables) located in Southern and Central Finland.Contents of Pb and Cd were analysed by GFAAS after wet digestion using concentrated HNO3.The contents of heavy metals in berries and vegetables were either very low, at the same level or lower than reported earlier from Sweden, the Netherlands and the USA. The mean contents of Pb (g/kg) and Cd (g/kg) in berries and vegetables on the Finnish Market in 1987 were respectively: strawberry 11, 24; black currant 23, 2; red currant 27, 7; apple 2, <1; tomato 3, 2; cucumber 2, <1; carrot 8, 10; onion 4, 18; white cabbage 3, 3; cauliflower 6, 5 and lettuce 8, 13.The results of the present study are in agreement with those of a Finnish Market Basket study showing that berries and vegetables only slightly contribute to the total lead and cadmium intake in Finland. 相似文献
6.
The effects of four wash procedures on the concentration of chromium in a pooled sample of human scalp hair are compared. The wash solutions examined are Triton X-100, sodium lauryl sulphate, acetone, and a mixture (1 + 1) of hexane and ethanol. The plateaux reached for hair chromium concentration are functions of the number of washings, and are characteristic for each wash solution. The wash procedure recommended involves two 20-min washes with aqueous 1% sodium lauryl sulphate solution after a hexane rinse. 相似文献
7.
Three non-specific methods for the extraction of total petroleum hydrocarbons (TPH) from soil into organic solvent were compared.
The techniques used for sample preparation were Soxhlet extraction, closed-vessel microwave-assisted extraction, and CEN shake
extraction. The total concentrations of extracted compounds in the boiling point range of C10–C40 were determined by gas chromatography
with flame ionization detection. The best recovery (99%) and repeatability (±3%) from standard oil mixtures were obtained
with microwave-assisted extraction. However, the different extraction methods exhibited different behaviour when spiked soil
samples were extracted. The best repeatability was obtained with CEN shake extraction (±6%) but the repeatability values for
Soxhlet and microwave-assisted methods were quite high (>20%). However, the larger uncertainties of the latter extraction
methods does not necessarily limit the applicability of these methods to the determination of petroleum hydrocarbons in soil,
as in the assessment of soil contamination the expanded uncertainty of the result is usually not limited by analytical uncertainty,
but rather by the uncertainty of the primary sampling stage. However, distinctive variation found in the chromatographic profiles
illustrates that discretion should be obeyed when chromatograms obtained after application of different extraction methods
on petroleum contaminated samples are to be used in the fingerprinting or age dating studies. Otherwise, misleading conclusions
concerning the age of spillage could be drawn. 相似文献
8.
Tyrode E Johnson CM Kumpulainen A Rutland MW Claesson PM 《Journal of the American Chemical Society》2005,127(48):16848-16859
The OH stretching region of water molecules in the vicinity of nonionic surfactant monolayers has been investigated using vibrational sum frequency spectroscopy (VSFS) under the polarization combinations ssp, ppp, and sps. The surface sensitivity of the VSFS technique has allowed targeting the few water molecules present at the surface with a net orientation and, in particular, the hydration shell around alcohol, sugar, and poly(ethylene oxide) headgroups. Dramatic differences in the hydration shell of the uncharged headgroups were observed, both in comparison to each another and in comparison to the pure water surface. The water molecules around the rigid glucoside and maltoside sugar rings were found to form strong hydrogen bonds, similar to those observed in tetrahedrally coordinated water in ice. In the case of the poly(ethylene oxide) surfactant monolayer a significant ordering of both strongly and weakly hydrogen bonded water was observed. Moreover, a band common to all the surfactants studied, clearly detected at relatively high frequencies in the polarization combinations ppp and sps, was assigned to water species located in proximity to the surfactant hydrocarbon tail phase, with both hydrogen atoms free from hydrogen bonds. An orientational analysis provided additional information on the water species responsible for this band. 相似文献
9.
Tolonen A Uusitalo J Hohtola A Jalonen J 《Rapid communications in mass spectrometry : RCM》2002,16(5):396-402
Hypericum perforatum L. (St. John's Wort) has long been known as a medicinal plant, and has been used for the treatment of depression and neuralgic disorders. Its main active constituents are believed to be a naphthodianthrone, hypericin, and a phloroglucinol, hyperforin. A sensitive high performance liquid chromatography (HPLC)/electrospray tandem mass spectrometric method for fast simultaneous determination of six major naphthodianthrones and phloroglucinols of Hypericum perforatum extract has been developed. The method, based on multiple dissociation reaction monitoring (MRM), allows the analysis of hypericin, protohypericin, pseudohypericin, protopseudo-hypericin, hyperforin and adhyperforin from the extract in less than 5 min. Good linearity over the range 0.1-1000 ng/mL for hyperforin and 2-500 ng/mL for hypericin was observed. Intra-assay accuracy and precision varied from 2 to 19% within these ranges. Lower levels of quantitation for hyperforin were 0.5 ng/mL and 2 ng/mL for hypericin. 相似文献
10.