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排序方式: 共有89条查询结果,搜索用时 15 毫秒
1.
K. Jaques W. Buda L. Dumortier J. Van der Eycken Arnold Venema Pat Sandra 《Journal of separation science》1994,17(2):72-73
Capillary GC on permethyl α-, β-, and γ-cyclodextrins has been applied to separate and quantify the enantiomers of some 2,3-iso-propylidene-1,2,3-cyclohexanetriol derivatives. Quantitative CGC data are compared to those obtained with chiral shift 1H NMR. 相似文献
2.
A device to derivatize amino acids with o-phthaldialdehyde, which is directly connected to high-performance liquid chromatographic equipment is described. Its principle is that a sample (10-500 microliters) is mixed with a reagent (containing o-phthaldialdehyde, 2-mercaptoethanol and sodium hydrogen carbonate buffer), using a peristaltic pump. This mixture is pumped into a loop of a pneumatically controlled injection valve at atmospheric pressure. When the derivatization is complete the valve switches, so that the sample is applied to a column and the amino acid derivatives are separated with a gradient of methanol-phosphate buffers. The reproducibility is such that brain perfusates or tissue extracts can be analyzed for the amino acid transmitter content and no internal standard is necessary. The major advantages of the present device are that it produces thorough mixing of reagent and sample, so that a high and constant degree of derivatization occurs (thus producing high sensitivity; less than 0.1 pmol can be detected) and its low cost. 相似文献
3.
Testing polyethylene materials for stress cracking resistance at elevated temperatures in the presence of a detergent solution is relatively popular. The detergents used for these tests are—to our knowledge—only of the ethoxylated nonylphenol type (trade names: Igepal, Antharox, Arkopal). Extensive investigations of solutions of these nonionic detergents used at 80 °C have shown that they are very susceptible to oxidation. Oxidation has already started after about one day at 80 °C and leads to erroneous failure times of polyethylene test bars exposed to the detergent and to an unacceptably large scatter in the data.
An alternative anionic alkylbenzene sulphonate (ABS) detergent has been tested which, when dissolved in drinking water, produces reproducible failure times of welded polyethylene samples, if the age of the detergent solution does not exceed about 2000 h at 80 °C. 相似文献
4.
Frequent in vivo sampling of blood proteins is often stressful, making it difficult to obtain more than a few samples. As a result, only limited time-profiles can be made. We have developed an ultrafiltration collection device (UCD) for continuous sampling. The UCD consists of a hollow fiber, a coil and a flow creator. Hollow fiber membranes are often hydrophobic and this can result in adsorption of protein and/or peptides, leading to clogged membranes. Adsorption was tested with a hydrophobic and hydrophilic peptide and two biocompatible hollow fibers made from different materials. The hollow fiber made from poly(ethylene) coated with ethylenevinyl alcohol gave near 100% recovery for both peptides. This was in contrast to the poly(sulfone) hollow fiber when sampling the hydrophobic peptide. Filling the coil with various peptide concentrations gave good recovery and insignificant diffusion even after storage for 6 d at 37 degrees C. Continuous pulse-free sampling was tested by vacuum. An average flow rate of 423 +/- 50 nl min(-1) over a period of 4 d was created using S-Monovette. The flow rate gradually declined during this period by <5% every consecutive day. In addition, we also examined a complex sample-serum in the poly(ethylene) hollow fiber. Serum and ultrafiltrate were spotted onto a protein chip and analyzed by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Six proteins out of 64 were found to be significantly different between serum and the ultrafiltrate (p < 0.05). The UCD has the potential to be used for in vivo real-time monitoring. 相似文献
5.
A number of polysiloxanes have been shown to be sensitive to acids when dissolved in chloroform. At 26O°C polysiloxanes were found to degrade under the influence of several compounds used or produced during the preparation of glass capillary columns. 相似文献
6.
Thomas KJ Hill JP Grenier S Kim YJ Abbamonte P Venema L Rusydi A Tomioka Y Tokura Y McMorrow DF Sawatzky G van Veenendaal M 《Physical review letters》2004,92(23):237204
We have utilized resonant x-ray diffraction at the Mn L(II,III) edges in order to directly compare magnetic and orbital correlations in Pr0.6Ca0.4MnO3. Comparing the widths of the magnetic and orbital diffraction peaks, we find that the magnetic correlation length exceeds that of the orbital order by nearly a factor of 2. Furthermore, we observe a large (approximately 3 eV) spectral weight shift between the magnetic and orbital resonant line shapes, which cannot be explained within the classic Goodenough picture of a charge-ordered ground state. To explain the shift, we calculate the orbital and magnetic resonant diffraction line shapes based on a relaxed charge-ordered model. 相似文献
7.
A dispersion equation for low-frequency waves in a fully ionized plasma with slowly varying density and magnetic field is derived from the two-fluid equations. The solutions are discussed in several limiting cases. Phase-velocity and refractive index surfaces are presented for the fast and slow magneto-acoustic waves and for the shear-Alfvén wave, influenced by the inhomogeneity drifts. 相似文献
8.
F. D. Berg M. Pfeiffer O. Schwalb M. Appenheimer W. Döring M. Franke W. Kühn V. Metag W. Niebur R. Novotny J. Ritman M. Röbig H. Ströher A. Boonstra H. Löhner A. Raschke L. Venema H. W. Wilschut N. Brummund W. Henning S. Hlavac R. Holzmann R. S. Simon 《Zeitschrift für Physik A Hadrons and Nuclei》1990,337(3):351-352
π0 -production probability of (9± 2)· 10? 3 per20Ne+Al reaction has been measured at 350 MeV/u using the Two Arm Photon Spectrometer TAPS. This yield is consistent with an interpolation of published π-production rates in heavy ion collisions. 相似文献
9.
Arnold Venema 《Journal of separation science》1990,13(8):537-539
The scope of the headspace sampling technique for the analysis of solid samples is discussed, and the static and the dynamic headspace methods compared. Theoretical aspects relating to quantification are discussed. The paper considers both instrumental requirements and applications. 相似文献
10.
Cecile Veerman Leonard M. C. Sagis Paul Venema Erik van der Linden 《Rheologica Acta》2005,44(3):244-249
To probe the behaviour of fibrillar assemblies of ovalbumin under oscillatory shear, close to the percolation concentration, cp (7.5%), rheo-optical measurements and Fourier transform rheology were performed. Different results were found close to cp (7.3%), compared to slightly further away from cp (6.9 and 7.1%). For 6.9 and 7.1%, a decrease in complex viscosity, and a linear increase in birefringence, n, with increasing strain was observed, indicating deformation and orientation of the fibril clusters. For 7.3%, a decrease in complex viscosity was followed by an increase in complex viscosity with increasing strain, which coincided with a strong increase in n, dichroism, n, and the intensity of the normalized third harmonic (I3/I1). This regime was followed by a second decrease in complex viscosity, where n,n and I3/I1 decreased. In the first regime where the viscosity was decreasing with increasing strain, deformation and orientation of existing clusters takes place. At higher oscillatory shear, a larger deformation occurs and larger structures are formed, which is most likely aggregation of the clusters. Finally, at even higher strains, the clusters break up again. An increase in complex viscosity, n, n and I3/I1 was observed when a second strain sweep was performed 30 min after the first. This indicates that the shear-induced cluster formation and break up are not completely reversible, and the initial cluster size distribution is not recovered after cessation of flow. 相似文献