TY - JOUR A1 - Adebayo, Segun Emmanuel A1 - Hashim, Norhashila A1 - Hass, Roland A1 - Reich, Oliver A1 - Regen, Christian A1 - Münzberg, Marvin A1 - Abdan, Khalina A1 - Hanafi, Marsyita A1 - Zude-Sasse, Manuela T1 - Using absorption and reduced scattering coefficients for non-destructive analyses of fruit flesh firmness and soluble solids content in pear JF - Postharvest Biology and Technology N2 - Quality attributes of fruit determine its acceptability by the retailer and consumer. The objective of this work was to investigate the potential of absorption (μa) and reduced scattering (μs’) coefficients of European pear to analyze its fruit flesh firmness and soluble solids content (SSC). The absolute reference values, μa* (cm−1) and μs’* (cm−1), of pear were invasively measured, employing multi-spectral photon density wave (PDW) spectroscopy at preselected wavelengths of 515, 690, and 940 nm considering two batches of unripe and overripe fruit. On eight measuring dates during fruit development, μa and μs’ were analyzed non-destructively by means of laser light backscattering imaging (LLBI) at similar wavelengths of 532, 660, and 830 nm by means of fitting according to Farrell’s diffusion theory, using fix reference values of either μa* or μs’*. Both, the μa* and the μa as well as μs’* and μs’ showed similar trends. Considering the non-destructively measured data during fruit development, μa at 660 nm decreased 91 till 141 days after full bloom (dafb) from 1.49 cm−1 to 0.74 cm−1 due to chlorophyll degradation. At 830 nm, μa only slightly decreased from 0.41 cm−1 to 0.35 cm−1. The μs’ at all wavelengths revealed a decreasing trend as the fruit developed. The difference measured at 532 nm was most pronounced decreasing from 24 cm−1 to 10 cm−1, while at 660 nm and 830 nm values decreased from 15 cm−1 to 13 cm−1 and from 10 cm−1 to 8 cm−1, respectively. When building calibration models with partial least-squares regression analysis on the optical properties for non-destructive analysis of the fruit SSC, μa at 532 nm and 830 nm resulted in a correlation coefficient of R = 0.66, however, showing high measuring uncertainty. The combination of all three wavelengths gave an enhanced, encouraging R = 0.89 for firmness analysis using μs’ in the freshly picked fruit. KW - Absorption KW - Non-destructive KW - Pear KW - Quality KW - Scattering Y1 - 2017 U6 - https://doi.org/10.1016/j.postharvbio.2017.04.004 SN - 0925-5214 SN - 1873-2356 VL - 130 SP - 56 EP - 63 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Bressel, Katharina A1 - Müller, Wenke A1 - Leser, Martin Erwin A1 - Reich, Oliver A1 - Hass, Roland A1 - Wooster, Tim J. T1 - Depletion-induced flocculation of concentrated emulsions probed by photon density wave spectroscopy JF - Langmuir N2 - Stable, creaming-free oil in water emulsions with high volume fractions of oil (phi = 0.05-0.40, density matched to water) and polysorbate 80 as an emulsifier were characterized without dilution by Photon Density Wave spectroscopy measuring light absorption and scattering behavior, the latter serving as the basis for droplet size distribution analysis. The emulsion with phi = 0.10 was used to investigate flocculation processes induced by xanthan as a semi-flexible linear nonabsorbing polymer. Different time regimes in the development of the reduced scattering coefficient mu(s)' could be identified. First, a rapid, temperature-dependent change in mu(s)' during the depletion process was observed. Second, the further decrease of mu(s)' follows a power law in analogy to a spinodal demixing behavior, as described by the Cahn-Hilliard theory. Y1 - 2020 U6 - https://doi.org/10.1021/acs.langmuir.9b03642 SN - 0743-7463 VL - 36 IS - 13 SP - 3504 EP - 3513 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Bressel, Lena A1 - Hass, Roland A1 - Reich, O. T1 - Particle sizing in highly turbid dispersions by Photon Density Wave spectroscopy JF - JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER N2 - Photon Density Wave (PDW) spectroscopy is presented as a fascinating technology for the independent determination of scattering (mu(s)’ and absorption (ita) properties of highly turbid liquid dispersions. The theory is reviewed introducing new expressions for the PDW coefficients k(I) and k(Phi). Furthermore, two models for dependent scattering, namely the hard sphere model in the Percus-Yevick Approximation (HSPYA) and the Yukawa model in the Mean Spherical Approximation (YMSA), are experimentally examined. On the basis of the HSPYA particle sizing is feasible in dispersions of high ionic strength. It is furthermore shown that in dialyzed dispersions or in technical copolymers with high particle charge only the YMSA allows for correct dilution-free particle sizing. (C) 2013 Elsevier Ltd. All rights reserved. KW - Photon Density Wave spectroscopy KW - Multiple light scattering KW - Dependent light scattering KW - Percus-Yevick model KW - Yukawa model KW - Particle sizing KW - Polymer dispersions Y1 - 2013 U6 - https://doi.org/10.1016/j.jqsrt.2012.11.031 SN - 0022-4073 VL - 126 IS - 1 SP - 122 EP - 129 PB - PERGAMON-ELSEVIER SCIENCE LTD CY - OXFORD ER - TY - JOUR A1 - Haene, Janick A1 - Bruehwiler, Dominik A1 - Ecker, Achim A1 - Hass, Roland T1 - Real-time inline monitoring of zeolite synthesis by Photon Density Wave spectroscopy JF - Microporous and mesoporous materials : zeolites, clays, carbons and related materials N2 - The formation process of zeolite A (Linde Type A) was monitored inline at 1.5 L scale by Photon Density Wave (PDW) spectroscopy as novel process analytical technology for highly turbid liquid suspensions. As a result, the reduced scattering coefficient, being a measure for particle number, size, and morphology, provides distinct process information, including the formation of amorphous particles and their transfer into crystalline zeolite structures. The onset and end of the crystallization process can be detected inline and in real-time. Analyses by powder X-ray diffraction and electron microscopy, based on a sampling approach, support the interpretation of the results obtained by PDW spectroscopy. In addition, the influence of the molar water content was investigated, indicating a linear increase of the time needed to reach the end of the zeolite A crystallization with increasing molar water content. Further experiments indicate a strong influence of the silica source on the course of the crystallization. The applicability of PDW spectroscopy under even more demanding chemical and physical conditions was investigated by monitoring the synthesis of zeolite L (Linde Type L). KW - Photon density wave spectroscopy KW - Process analytical technology KW - Zeolite synthesis KW - Molar water content KW - Silica source Y1 - 2019 U6 - https://doi.org/10.1016/j.micromeso.2019.109580 SN - 1387-1811 SN - 1873-3093 VL - 288 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hartwig, Anne A1 - Hass, Roland T1 - Monitoring lactose crystallization at industrially relevant concentrations by photon density wave spectroscopy JF - Chemical engineering & technology N2 - Lactose is of great industrial importance and its production includes the cooling crystallization from highly concentrated solutions. Monitoring the crystallization process is essential to ensure reproducible product quality. Photon density wave (PDW) spectroscopy enables in-line monitoring of highly concentrated processes in liquid dispersions. It was applied to the determination of the solubility and nucleation points of lactose monohydrate in water, sizing of lactose crystals, and to dissolution as well as crystallization monitoring. Other process analytical technologies (focused-beam reflectance measurement, particle vision and measurement) were used as reference, and the comparison indicates that PDW spectroscopy is very robust against probe fouling and is, thus, a useful tool for monitoring crystallization processes in concentrated suspensions. KW - In-line monitoring KW - Lactose KW - Light scattering KW - Photon density wave spectroscopy KW - Process analytical technology Y1 - 2018 U6 - https://doi.org/10.1002/ceat.201700685 SN - 0930-7516 SN - 1521-4125 VL - 41 IS - 6 SP - 1139 EP - 1146 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hass, Roland A1 - Munzke, Dorit A1 - Reich, Oliver T1 - Inline-Partikelgroeßenmesstechniken fuer Suspensionen und Emulsionen N2 - Die Inline-Bestimmung von Teilchengroeßen in Emulsionen und Suspensionen stellt besondere Anforderungen an die Messtechnik, da auch bei sehr hohen Teilchenkonzentrationen im Prozess verduennungsfreie Analytik betrieben werden soll. Neben einer Klaerung der Begriffe atline, online und in-line gibt der Beitrag eine Einfuehrung in die mathematische Beschreibung von Groeßenverteilungen. Als Inline-Techniken werden Photonendichtewellen-Spektroskopie, Focused Beam Reflectance Measurement und Ultraschallextinktion-Spektroskopie diskutiert und ihre sehr unterschiedlichen physikalischen Messprinzipien erlaeutert. Auch wird kurz erklaert, wie Teilchengroeßen aus den Messresultaten erhalten werden. Die wesentlichen Charakteristika dieser drei Methoden werden abschließend im ueberblick dargestellt. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/60500203/ U6 - https://doi.org/10.1002/cite.200900172 SN - 0009-286X ER - TY - JOUR A1 - Hass, Roland A1 - Munzke, Dorit A1 - Ruiz, Salome Vargas A1 - Tippmann, Johannes A1 - Reich, Oliver T1 - Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy JF - Analytical & bioanalytical chemistry N2 - In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (mu (a) and mu (s)', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches. KW - Photon Density Wave spectroscopy KW - Enzymatic milk coagulation KW - Beer mashing KW - Human donor blood KW - Process analytical technology KW - Light scattering Y1 - 2015 U6 - https://doi.org/10.1007/s00216-015-8513-9 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 10 SP - 2791 EP - 2802 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Hass, Roland A1 - Münzberg, Marvin A1 - Bressel, Lena A1 - Reich, Oliver T1 - Industrial applications of photon density wave spectroscopy for in-line particle sizing [Invited] JF - Applied optics N2 - Optical spectroscopy in highly turbid liquid material is often restricted by simultaneous occurrence of absorption and scattering of light. Photon Density Wave (PDW) spectroscopy is one of the very few, yet widely unknown, technologies for the independent quantification of these two optical processes. Here, a concise overview about modern PDW spectroscopy is given, including all necessary equations concerning the optical description of the investigated material, dependent light scattering, particle sizing, and PDW spectroscopy itself. Additionally, it is shown how the ambiguity in particle sizing, arising from Mie theory, can be correctly solved. Due to its high temporal resolution, its applicability to highest particle concentrations, and its purely fiber-optical probe, PDW spectroscopy possesses all fundamental characteristics for optical in-line process analysis. Several application examples from the chemical industry are presented. (C) 2013 Optical Society of America Y1 - 2013 U6 - https://doi.org/10.1364/AO.52.001423 SN - 1559-128X SN - 2155-3165 VL - 52 IS - 7 SP - 1423 EP - 1431 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Hass, Roland A1 - Reich, Oliver T1 - Photon density wave spectroscopy for dilution-free sizing of highly concentrated nanoparticles during starved-feed polymerization JF - ChemPhysChem : a European journal of chemical physics and physical chemistry KW - analytical methods KW - fiber-optical spectroscopy KW - nanoparticles KW - photon density wave spectroscopy KW - polymerization Y1 - 2011 U6 - https://doi.org/10.1002/cphc.201100323 SN - 1439-4235 VL - 12 IS - 14 SP - 2572 EP - 2575 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Kutlug, Oezgür A1 - Hass, Roland A1 - Reck, Stephan A1 - Hartwig, Andreas T1 - Inline characterization of dispersion formation of a solvent-borne acrylic copolymer by Photon Density Wave spectroscopy JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - Most investigations on phase inversion (PI) of resins upon addition of water have been carried out by dynamic light scattering (DLS), torque, and viscosity measurements. The main problem, however, is analytic discontinuity due to sample removal and a changing matrix due to dilution during the preparation of the aqueous resin dispersions. This work presents Photon Density Wave (PDW) spectroscopy as a tool for the inline characterization of the acetone process for an acrylic copolymer with high acrylic acid (AA) content. PDW spectroscopy revealed different trends for optical properties compared to torque during water feed. Also the absence of PI due to dissolution of copolymer in the solvent/water mixture is observed by PDW spectroscopy. PI for the investigated copolymer did not occour during water feed but during removal of solvent. Different feeding rates of water gave similar trends while a change in temperature and degree of AA neutralization led to changes in optical properties and torque. Thermal processing showed that the optical properties of mixtures prior and after removal of solvent were completely different caused by changes of solubility. KW - Acetone process KW - Dispersion KW - Photon Density Wave spectroscopy KW - Radical polymerization KW - Torque KW - Turbid media Y1 - 2018 U6 - https://doi.org/10.1016/j.colsurfa.2018.08.011 SN - 0927-7757 SN - 1873-4359 VL - 556 SP - 113 EP - 119 PB - Elsevier CY - Amsterdam ER -