A robust analytical method is required for the determination of low-molecular weight organic acids, which are potential causes of refinery and internal combustion engine corrosion. The ion chromatographic method developed in this study allows the determination of acetic acid and formic acid in diesel oil mixtures with a motor oil volume fraction of up to 10%. The hydrophobic matrix is automatically removed in-line through a matrix elution step with organic solvent and nonaqueous anion-exchange analyte extraction. Acetic acid and formic acid, as the smallest and most acidic aliphatic naphthenic acids, were determined. Gradient anion-exchange chromatography on high-capacity columns in combination with suppressed conductivity detection allowed their selective and sensitive determination. Typical recovery values were from 82 to 107% for each acid in the matrices evaluated with reproducibility less than 5% for acid fortified samples. 相似文献
Recent optical and acoustical studies have shown a threshold behaviour in the response of phospholipid-coated contrast agents, for a certain range of sizes. Below the acoustic pressure threshold, the microbubbles’ scattering efficacy is significantly reduced compared to that above the threshold. Here we investigate the clinical relevance of the observed threshold behaviour. A cardiac ultrasound scanner system was used to analyse the pressure-dependence of the scatter intensity. The scattering of a native suspension of a phospholipid-coated contrast agent was compared to that of a suspension in which microbubbles with a size larger than 3.0 μm in diameter were extracted. A power modulation scheme at the fundamental frequency was applied. After linearly scaling and subtracting the B-mode images recorded at 70 and 200 kPa, the contrast-to-tissue ratio (CTR) of the native suspension was 3.2 dB, whereas the CTR of the filtered suspension was 20 dB. The 17 dB difference is attributed to the threshold behaviour. Well-established ultrasound imaging techniques such as fundamental power modulation imaging could benefit from the pressure-dependent scattering properties of this type of contrast microbubbles. 相似文献
Surface-enhanced resonance Raman scattering (SERRS) from dilute solutions (down to nanomolar concentrations) of human mono-oxygenase CYP2D6 is observed using aqueous dispersions of Ag nanoparticles (hydrosol) coated with self-assembled monolayers (SAMs) of mercaptoalkanoic acids of two different lengths. From a direct comparison with its resonance Raman spectrum in solution, CYP2D6 appears to fully retain its native structure upon adsorption on coated hydrosol through electrostatic interaction, while a structural change in the active site is observed when uncoated citrate-reduced hydrosol is used. Using SERRS on these biocompatible coated hydrosols, the effects of dextromethorphan on the enzyme's active site can be observed, demonstrating that CYP2D6 ability of binding substrates is preserved. Moreover, by tuning the wavelength of the exciting laser away from the main absorption band of the heme, the vibrational bands of the SAM coating are observed and analyzed to see how the presence of the protein affects the SAM structure. 相似文献
The production and use of naphthalene sulfonates can easily cause pollution of surface and other types of waters. In the present study, capillary electrophoresis in combination with UV absorption detection was used to separate 21 amino- and hydroxy-substituted naphthalene sulfonates which included multiple isomeric compounds. The influence of various parameters such as pH (which turned out to be extremely important), temperature of the surrounding air flow, and the use of buffer additives (micelles, cyclodextrins, organic modifiers) was studied. Complete separation of all analytes including the isomers, was achieved in two runs with a 50 mM boric acid/borate buffer, containing either 100 mM sodium dodecylsulfonate or 15% acetonitrile. The limits of detection obtained for the individual compounds typically were 20μgI−1. River water samples spiked at this concentration level could be analysed using a simple three-step sample clean-up procedure. 相似文献
To date, lasers are widely accepted tools in analytical spectroscopy, involved in various stand-alone and hyphenated techniques. Furthermore, significant progress can be noted in this field. In this paper, first of all some laser characteristics are discussed. Subsequently, five selected topics are outlined to illustrate recent achievements and future developments:
1. Laser-induced fluorescence for detection in capillary electrophoresis, including the use of ultraviolet, continuous-wave lasers in combination with wavelength-resolved emission detection; the use of diode laser-induced fluorescence in the red region of the electromagnetic spectrum and the use of Ti:sapphire lasers for multiphoton-excited fluorescence detection.
2. Degenerate four-wave mixing for detection in liquid microseparation systems (based on the coherence of laser light).
3. Fluorescence line-narrowing spectroscopy for identification purposes, a cryogenic high-resolution molecular fluorescence technique with a high potential in environmental analysis.
4. Recent developments in Raman spectroscopy (including ultraviolet-Resonance Raman and hyphenation of liquid chromatography and Raman spectroscopy).
5. Use of lasers for sample introduction in inorganic analysis based on controlled material ablation.
Many relations between the physical, rheological or mechanical properties of linear polymers and their molar mass are well known. For disperse polymers, parameters that express these relations are typically related to (a combination of) the moments of the molar‐mass distribution. Properties of branched, nonlinear polymers have been far more difficult to describe in the form of general relations. Monodisperse star polymers or regular stars, with a distinct number of arms and equal arm length, are the simplest member of the family of branched polymers and have served as model compounds in many studies. For these regular stars, the relation between zero shear viscosity and arm or span length has been determined. To establish equivalent relations for disperse star‐branched polymers, it is important to assess the span‐length distribution and its moments; these parameters can be calculated when the distribution of the molar mass of the arms of a star‐branched polymer is known, for instance, for a known polymerization mechanism.
Span‐length probability functions of star‐branched polycondensates with xn = 100: f = 1 (•), f = 2 (○), f = 3 (▪), f = 5 (□), and f = 10 (+). 相似文献
We report a series of Raman-Rayleigh-LIF measurements in two turbulent natural-gas jet diffusion flames produced by the Delft
piloted jet diffusion flame burner. The main objective of the Raman-Rayleigh-LIF measurements was to obtain detailed information
on the major species concentrations in the flames. The measurements provide simultaneous data on temperature, the concentrations
of the major species and the radicals OH and NO and mixture fraction. The application of the Raman technique in the undiluted
natural-gas flames proves to be very challenging because of the high fluorescence interference levels. The interference contributions
to the recorded Raman signals are identified and subtracted using empirical correlations between the Raman signals and the
signals on fluorescence interference monitor channels. The calibration and data reduction of the Raman-Rayleigh and LIF signals
are discussed in detail. The resulting dataset compares excellently with data from previous experiments. Because the Raman-Rayleigh-LIF
data provide quantitative concentrations and accordingly quantitative mixture fractions, they form a valuable and useful extension
of the existing database for the Delft piloted jet diffusion flame burner.
Received: 19 October 1999 / Revised version: 31 January 2000 / Published online: 7 June 2000 相似文献
This paper reports the photoluminescence and afterglow of Sr2SiO4 doped with Eu2+ and Dy3+. Factors governing the formation of the monoclinic or orthorhombic phase of this ortho-silicate are described and the impact of the crystallographic modification on the luminescence and afterglow under UV and VUV excitation are discussed and insight in factors limiting the efficiency of this yellow afterglow material is given. 相似文献
Irreversible optical sensing of humidity by a doped cholesteric liquid crystal is achieved by using a thin film of nematic host E7 with a binaphthylorthosilicate ester as dopant (guest). The film changes its color from blue (to green to orange to red) to colorless when exposed to humidity as the dopant is hydrolyzed. 相似文献