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991.
The synthesis of analogues of silandrin and hydnocarpin from 2-hydroxy-3,4-ethylenedioxychalcones has been achieved.KIEN, Karakalpak Division of the Academy of Sciences of Uzbekistan. Taras Shevchenko Kiev University. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 351–354, May–June, 1994. 相似文献
992.
Benzodioxane and benzodioxepane analogues of 5,7-dihydroxy-3,4-methylenedioxyisoflavone have been synthesized from -hetaryl-2,4,6-trihydroxyacetophenones. The structures of the compounds obtained have been shown by their PMR spectra.Taras Shevchenko Kiev University. KIEN, Karakalpak Division of the Academy of Sciences of the Republic of Uzbekistan, Nukus. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 343–347, May–June, 1994. 相似文献
993.
In this paper, we study the spectrum of the Dirichlet Laplacian in a bounded (or, more generally, of finite volume) open set R
n
(n1) with fractal boundary of interior Minkowski dimension (n–1,n]. By means of the technique of tessellation of domains, we give the exact second term of the asymptotic expansion of the counting functionN() (i.e. the number of positive eigenvalues less than ) as +, which is of the form /2 times a negative, bounded and left-continuous function of . This explains the reason why the modified Weyl-Berry conjecture does not hold generally forn2. In addition, we also obtain explicit upper and lower bounds on the second term ofN(). 相似文献
994.
U. Wollenberger B. Neumann K. Riedel F. W. Scheller 《Fresenius' Journal of Analytical Chemistry》1994,348(8-9):563-566
Biosensors employing a biocatalyst on a different level of integration have been developed for monitoring environmental pollution. These probes range from laboratory specimen to commercial detectors applied to analyzers. Recent developments on amperometric enzyme and microbial biosensors are presented here. A monoenzymatic bulk-type carbon electrode is described for biosensing organic hydroperoxides in aqueous solutions; peroxidase is immobilized within the electrode body and the direct electron transfer between electrode and enzyme is measured. Both, reversible and irreversible inhibitors of acetylcholinesterase have been quantified by using a kinetically controlled acetylcholine enzyme sequence electrode. The inhibitory effect of pesticides such as butoxycarboxime, dimethoate, and trichlorfon could be quantified within 6 min in molar concentrations. Different multi-enzyme electrodes have been developed for the determination of inorganic phosphate. These sensors represent examples of sequentially acting enzymes in combination with enzymatic analyte recycling. Using this type of amplification nanomolar concentrations can be measured. 相似文献
995.
V. Brüser S. Jakobs H. -H. Möbius U. Schönauer 《Fresenius' Journal of Analytical Chemistry》1994,349(8-9):684-687
Solid electrolyte cells for detecting NO2 with Ba(NO3)2 or Sr(NO3)2 partially replaced by -Al2O3 as solid electrolytes have been studied. The cell tension depends on the NO2- as well as on the NO-concentration. Investigations of the establishment of the NO2-NO-O2-equilibrium by the catalytic effects of the used electrode materials Pt and Au have shown that a decomposition of NO2 below 400°C cannot be expected.17th Communication on oxoanionic solid electrolytes and their possible applications; 16th Communication see Solid State Ionics 51:183–185 (1992)Extension of a part of the lecture of V. Brüser, S. Jakobs, H.-H. Möbius and U. Schönauer Galvanische NO2-Sensoren mit Nitrat-Festelektrolyten given in Feldberg, 3. 6. 1993 相似文献
996.
B. Bastian T. P. Knepper P. Hoffmann H. M. Ortner 《Fresenius' Journal of Analytical Chemistry》1994,348(10):674-679
A method for the identification and quantification of aromatic sulfonic acids in industrial waste water has been developed. The preparation of the samples comprises a clean-up step and an enrichment step, utilizing i) reversed-phase extraction and ii) ion-pair solid phase extraction. The aromatic sulfonic acids are separated by ion-pair chromatography with diode-array detection. An advantage of the developed ion-pair chromatographic method is the separation of linear alkylbenzenesulfonic acids (LAS), lignosulfonic acids and aromatic sulfonic acids in one chromatographic run. Also described is an optimized clean-up procedure for collected fractions of a preparative chromatographic run to identify monosulfonic acids with GC/MS after methylation. The detection limits for aromatic sulfonic acids in industrial waste waters are at the g/l level. 相似文献
997.
The performance of a new separation technique for metal-speciation — capillary electrophoresis (CE) — is presented. Polyhydroxy compounds such as polyphenols and organic tanning agents can be determined in the g/L range. Certain complexes of these compounds with iron (III) ions may also be directly or indirectly verified. The work has shown that it is possible to determine certain complexes existing in beverages (tea and coffee) by decomplexation with chelating agents (CDTA). The ligands released can be separated by CE and identified by their migration time and UV/VIS absorption spectra. 相似文献
998.
Ying-Sing Fung Andrew Shin-Kwan Tang 《Fresenius' Journal of Analytical Chemistry》1994,350(12):721-723
A fast, simple and reliable method for the analysis of DEHP in PVC products was developed using a one-step Soxhlet extraction prior to HPLC determination. The linear range from 1.25 /g to 250 mg/g of DEHP in PVC was found sufficient to cover the normal concentrations encountered. The reliability of the method was established by comparison with the ASTM method and no potential interferent was identified except a large concentration of DIMP. 相似文献
999.
The limit of detection for the 4,6 dinitro-orthocresol (DNOC) pesticide, including small latex particles as light scattering samples in water as suspending medium, has been determined for the transversal photothermal deflection technique. The results where compared to conventional spectrophotometry. In the photothermal deflection experiments performed with a continuous Ar+-excitation beam (=363.8 nm) a LOD of 0.8 g/l is achieved for the DNOC in water.Awarded poster prize 相似文献
1000.