TY - JOUR A1 - Engelhard, Sonja A1 - Löhmannsröben, Hans-Gerd A1 - Schael, Frank T1 - Quantifying ethanol content of beer using interpretive near-infrared spectroscopy N2 - On the basis of absorption measurements in the near-infrared (NIR) spectral range, a new method for the quantification of the ethanol content of beer is presented. Instead of the multivariate calibration models most commonly employed in NIR spectroscopic works, we use interpretive difference spectroscopy: Two wavelengths are selected according to the assignment of the absorption bands of the main substances of content of beer in the NIR region, and the difference between the absorbances at these wavelengths is used for ethanol quantification. Absorption spectra of the dominating beer ingredients are discussed and the calibration procedure with ethanol/water mixtures is shown. Robustness against the carbohydrate content of beer samples was demonstrated by analyzing solutions of ethanol and maltose in water. Validation of the method was performed with various beer samples with an ethanol concentration range between 0.5 and 7.7 vol %. The pertinent advantage of the procedure developed in this work is the indication that the results are independent from seasonal variations of the ingredients, which is of high interest for products with natural ingredients such as beer Y1 - 2004 SN - 0003-7028 ER - TY - JOUR A1 - Schael, Frank A1 - Reich, Oliver A1 - Löhmannsröben, Hans-Gerd T1 - Near infrared diode laser spectroscopy of organic compounds in turbid aqueous solutions N2 - Diffuse reflectance measurements and photon migration studies with near infrared (NIR) diode lasers were employed to elucidate experimental methods for determining absorption and scattering coefficients and species concentrations in highly scattering solutions. Applicability of theoretical approaches were established by investigating model systems with absorbing (e.g. ink, malachite green) and scattering (e.g. milk powder, caolinit) species in aqueous solution. While diffuse reflectance measurements practically requires calibration procedures, photon migration studies allow quantitative determination of absorption and scattering coefficients of turbid solutions consistent with absorptions coefficients obtained from Lambert-Beer's law. Furthermore, NIR absorption spectra of water, chlorinated hydrocarbons (chloroform, 1,2-dichloroethane, trichloroethene) and of various sugars ($alpha$-D-glucose, sucrose, maltose) are discussed. Spectral variations of NIR water absorption with temperature and solvents are exammined. Exemplary, NIR diode laser detection of water in acetone/water mixtures is performed. Y1 - 2000 SN - 0-9528666-1-7 ER - TY - JOUR A1 - Löhmannsröben, Hans-Gerd A1 - Schael, Frank A1 - Reich, Oliver A1 - Lemke, Matthias A1 - Schober, Lars T1 - Untersuchung von organischer Bodensubstanz und Bodengasen mit laser-spektroskopischer in-situ Meßtechnik Y1 - 2000 ER - TY - JOUR A1 - Schael, Frank A1 - Engelhard, Sonja A1 - Reich, Oliver T1 - Optische Sensorik für die in-situ-Analytik von Brauprozessen Y1 - 2001 ER - TY - CHAP A1 - Asche, Hartmut A1 - Böckmann, Christine A1 - Laue, Steffen A1 - Löhmannsröben, Hans-Gerd A1 - Lemke, Matthias A1 - Schober, Lars A1 - Reich, Oliver A1 - Lück, Erika A1 - Schütte, Marc A1 - Domsch, Horst A1 - Makower, Alexander A1 - Scheller, Frieder W. A1 - Stöcklein, Wolfgang A1 - Wollenberger, Ursula A1 - Schultze, Rainer A1 - Hengstermann, Theo A1 - Schael, Frank T1 - Umweltforschung für das Land Brandenburg : Projekt Umweltanalytik / Umweltmeßtechnik / Informationssysteme Y1 - 2000 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-3862 SP - 176 EP - 227 ER - TY - GEN A1 - Reich, Oliver A1 - Löhmannsröben, Hans-Gerd A1 - Schael, Frank T1 - Optical sensing with photon density waves: investigation of model media N2 - Investigations with frequency domain photon density waves allow elucidation of absorption and scattering properties of turbid media. The temporal and spatial propagation of intensity modulated light with frequencies up to more than 1 GHz can be described by the P1 approximation to the Boltzmann transport equation. In this study, we establish requirements for the appropriate choice of turbid model media and characterize mixtures of isosulfan blue as absorber and polystyrene beads as scatterer. For these model media, the independent determination of absorption and reduced scattering coefficients over large absorber and scatterer concentration ranges is demonstrated with a frequency domain photon density wave spectrometer employing intensity and phase measurements at various modulation frequencies. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 026 Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13147 ER - TY - JOUR A1 - Schael, Frank A1 - Reich, Oliver T1 - In-situ-Analytik heterogener Medien mit frequenz- und leistungsmodulierten Diodenlasern N2 - Electronic intensity and frequency modulation of diode lasers enables new perspectives for highly sensitive analytical in-situ techniques. For analyis of "heterogeneous" media, which may consist of coexisting gaseous, liquid, and solid phases and often show multiple light scattering, non-invasive techniques with outstanding performance characteristics can be developed. Analysis of photon density waves launched by intensity-modulated lasers provide an elegant way for the determination of absorption and scattering coefficients of multiple scattering media. The absorption coefficient can be used for qualitative and quantitative analysis of chemical constituents (which absorb in the range of the laser wavelengths). The scattering coefficient allows characterization of physical and morphological properties of the sample. In the current work, applicability of appropriate radiation transport models was investigated with simple light scattering solutions and compared with results obtained from the treatment according to the theory of Kubelka and Munk. Measurements of human blood samples are discussed. A new method for determination of water vapor partial pressure in a polyurethane foam with a frequency-modulated external cavity diode laser is discussed. Y1 - 2001 ER -