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  • 1995-1999  (456)
  • 1920-1924
  • 1996  (456)
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  • 1995-1999  (456)
  • 1920-1924
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  • 1
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14–18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H2O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.
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  • 2
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The detection of small absorption differences is one of the basic requirements for the non-invasive determination of blood substrates. As conventional spectrometers are limited in their detection capabilities of small absorption changes, semiconductor lasers are applied for this purpose. By using a special modulation scheme, physiological glucose concentrations could be successfully predicted. The results demonstrate the feasibility of using small and inexpensive laser diodes for the spectroscopic determination of glucose in aqueous solutions as a step towards a portable non-invasive glucose sensor for self- monitoring of diabetic patients.
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  • 3
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The existence of isobaric and polyatomic ion interferences has been considered to be a significant shortcoming of inductively coupled plasma – mass spectrometry (ICP-MS). In the special case of Mo-Zr-alloys problems caused by polyatomic ions are substantial. The determination of trace elements by using classical univariate linear regression of single signals or any correction equations presented by the instrumental software is impossible. There are various possibilities to overcome spectral interferences, in principle. The application of high-resolution ICP-MS, separation methods or alternative sample introduction systems is limited by the high cost and the apparative expenditure. In this report methods of multisignal calibration, like partial least squares (PLS) regression and canonical correlation analysis (CCA), are used to overcome isobaric or chemical interferences in ICP-MS. It is shown, that PLS and CCA are able to handle or tolerate, respectively, spectral interferences existing in a Mo-Zr-O-H-F system. The results of quantitative analysis provided by PLS and CCA were comparable.
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  • 4
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A computer-program “IR-Spectroscopy” for the interpretation of infrared spectra of organic compounds is described. It contains the following basic items for preprocessing and execution of the computer based interpretation process: handling of the rule-base CorTab, routines for automatic rule generation and interpretation modules on the basis of the programming languages PROLOG and C.
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  • 5
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The suitability of an integrated optical chemical sensor for the determination of highly volatile chlorinated hydrocarbons in aqueous solutions has been proven. The analytes are detected by NIR absorption spectrometry in the evanescent field of an integrated optical strip waveguide generated in a BGG31 (Schott, Germany) glass substrate, which is coated with a hydrophobic polymer superstrate as sensing layer. It has been shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepared by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t90-value) are between five and fourteen minutes for a coating thickness of around 30 μm. The sensor response is totally reversible. The analyte desorbes in air within 2 min. The enrichment of trichloroethene in the polysiloxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step.
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  • 6
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An home-made EFA (evanescent field absorbance)-sensor has been tested for the determination of hydrocarbons in water. The investigations have been performed both with crude oil emulsions and petrol solutions. Cuvette and evanescent wave spectra of crude oil and petrol in the near-infrared region are presented and discussed. The concentration of aromatic compounds in crude oil can be determined semiquantitatively by the standard addition method. The sorption behaviour of the hydrocarbons in the cladding of the fiberoptic sensor has been investigated and a correlation between the sensor signal and the concentration of the aqueous hydrocarbon emulsion/solution could be shown. The desorption of the enriched molecules after the measurements is also presented. The petrol molecules evaporate in ambient air so that the sensor is easily regenerated. In case of oil measurements the hydrocarbon molecules cannot be removed by rinsing the sensor with clear water or by evaporating them in ambient air. It has to be regenerated by washing it with a high volatile solvent instead.
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  • 7
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A method for the ion chromatographic separation of cationic CrFx-species in aqueous acidic solutions with photometric detection is described. CrF3-, CrF+ 2- and CrF2+-species can be separated on a commercial cation-exchange column using HCl/2,3-diaminopropionic acid (DAP) as eluent. The chromium(III)-complexes are converted with 2,6- pyridinedicarboxylic acid (PDCA) into the violet [Cr(PDCA)2]--complex at temperatures 〉90 °C by post-column derivatisation for the subsequent spectrophotometric detection at λ=335 nm. Iron- and nickel-ions do not disturb the determination even in concentrations higher than those of the chromium (III)-ions.
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  • 8
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The applicability of simultaneous ICP-OES for the accurate analysis of soft magnetic alloys has been investigated. Long-time signal variations of up to 40% can be observed under normal operating conditions. The scattering of the values can largely be compensated by a correction procedure with internal and external standardization where the intensity value of the analytical signal is first rationed to the simultaneously measured intensity of an internal standard line and after that recalibrated with an external standard. Not only the trueness but also the precision could be improved by using Cd as a real-time internal standard. This is attributed to a compensation for instrumental fluctuations as a result of the simultaneous measurement of both emission signals.
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  • 9
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Neutron activation analysis (NAA) has been used as detection technique for adsorbable organic fluorine in aqueous samples. The results have been compared with the standardized DIN method which uses a fluoride-ion-selective electrode (ISE).
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  • 10
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A technique for precise boron isotope ratio measurements with a high detection power has been developed by negative thermal ionization mass spectrometry (NTIMS). Relative standard deviations in the range of 0.03–0.3% have been obtained for the determination of the 11B/10B isotope ratio using nanogram amounts of boron. Ba(OH)2 has been applied as ionization promoter for the formation of negative thermal ions. By adding MgCl2 better reproducibilities of the measurement have been achieved. A possible interference of BO- 2 ions at mass number 42 by CNO- could be excluded by the sample preparation technique used. Contrary to other NTI techniques no dependence of the measured isotope ratio on the boron amount used has been observed. Anthropogenic and natural saline influences in ground water have been successfully identified by boron isotope ratio determinations with this NTIMS method, due to the different isotopic composition of boron in natural and anthropogenic substances. In sewage, the boron isotope ratio is substantially influenced by washing powder, which contains low 11B/10B ratios (expressed in δ11B values normalized to the standard reference material NIST SRM 951). In contaminated ground water, low δ11B values are normally correlated with high boron and high chloride concentrations. On the other hand, δ11B shifts to higher values in less contaminated samples. For ground water with saline influences, only the δ11B determination, and not the boron or chloride content, allowed the correct identification of this natural source of contamination.
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