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Grimes MI, Cheeks M, Smith J, Zurlo F, Mantle MD. Decoupling Protein Concentration and Aggregate Content Using Diffusion and Water NMR. Anal Chem 2024; 96:11155-11162. [PMID: 38943616 PMCID: PMC11256015 DOI: 10.1021/acs.analchem.3c05875] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Revised: 05/30/2024] [Accepted: 06/18/2024] [Indexed: 07/01/2024]
Abstract
Protein-based biopharmaceutical drugs, such as monoclonal antibodies, account for the majority of the best-selling drugs globally in recent years. For bioprocesses, key performance indicators are the concentration and aggregate level for the product being produced. In water NMR (wNMR), the use of the water transverse relaxation rate [R2(1H2O)] has been previously used to determine protein concentration and aggregate level; however, it cannot be used to separate between them without using an additional technique. This work shows that it is possible to "decouple" these two key characteristics by recording the water diffusion coefficient [D(1H2O)] in conjunction with R2(1H2O), even in the event of overlap in either D(1H2O) or R2(1H2O). This method is demonstrated on three different systems, following appropriate D(1H2O) or R2(1H2O) calibration data acquisition for a protein of interest. Our method highlights the potential use of benchtop NMR as an at-line process analytical technique.
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Affiliation(s)
- Mark I. Grimes
- Department
of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
| | - Matthew Cheeks
- Cell
Culture & Fermentation Sciences, Biopharmaceutical Development,
Biopharmaceuticals R&D, AstraZeneca, Francis Crick Avenue, Cambridge CB2 0AA, U.K.
| | - Jennifer Smith
- Cell
Culture & Fermentation Sciences, Biopharmaceutical Development,
Biopharmaceuticals R&D, AstraZeneca, Francis Crick Avenue, Cambridge CB2 0AA, U.K.
| | - Fabio Zurlo
- Cell
Culture & Fermentation Sciences, Biopharmaceutical Development,
Biopharmaceuticals R&D, AstraZeneca, Francis Crick Avenue, Cambridge CB2 0AA, U.K.
| | - Mick D. Mantle
- Department
of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
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2
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Schiewe T, Gutschmann B, Santolin L, Waldburger S, Neubauer P, Hass R, Riedel SL. Real-time monitoring of biomass during Escherichia coli high-cell-density cultivations by in-line photon density wave spectroscopy. Biotechnol Bioeng 2023; 120:2880-2889. [PMID: 37272419 DOI: 10.1002/bit.28460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 05/19/2023] [Accepted: 05/22/2023] [Indexed: 06/06/2023]
Abstract
An efficient monitoring and control strategy is the basis for a reliable production process. Conventional optical density (OD) measurements involve superpositions of light absorption and scattering, and the results are only given in arbitrary units. In contrast, photon density wave (PDW) spectroscopy is a dilution-free method that allows independent quantification of both effects with defined units. For the first time, PDW spectroscopy was evaluated as a novel optical process analytical technology tool for real-time monitoring of biomass formation in Escherichia coli high-cell-density fed-batch cultivations. Inline PDW measurements were compared to a commercially available inline turbidity probe and with offline measurements of OD and cell dry weight (CDW). An accurate correlation of the reduced PDW scattering coefficient µs ' with CDW was observed in the range of 5-69 g L-1 (R2 = 0.98). The growth rates calculated based on µs ' were comparable to the rates determined with all reference methods. Furthermore, quantification of the reduced PDW scattering coefficient µs ' as a function of the absorption coefficient µa allowed direct detection of unintended process trends caused by overfeeding and subsequent acetate accumulation. Inline PDW spectroscopy can contribute to more robust bioprocess monitoring and consequently improved process performance.
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Affiliation(s)
- Thomas Schiewe
- Institute of Chemistry, innoFSPEC, University of Potsdam, Potsdam, Germany
- PDW Analytics GmbH, Potsdam, Germany
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
| | - Björn Gutschmann
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
| | - Lara Santolin
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
| | - Saskia Waldburger
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
| | - Peter Neubauer
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
| | - Roland Hass
- Institute of Chemistry, innoFSPEC, University of Potsdam, Potsdam, Germany
- PDW Analytics GmbH, Potsdam, Germany
| | - Sebastian L Riedel
- Institute of Biotechnology, Chair of Bioprocess Engineering, Technische Universität Berlin, Berlin, Germany
- Department VIII-Mechanical Engineering, Event Technology and Process Engineering, Environmental and Bioprocess Engineering Laboratory, Berliner Hochschule für Technik, Berlin, Germany
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3
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Schlappa S, Bressel L, Reich O, Münzberg M. Advanced Particle Size Analysis in High-Solid-Content Polymer Dispersions Using Photon Density Wave Spectroscopy. Polymers (Basel) 2023; 15:3181. [PMID: 37571075 PMCID: PMC10421201 DOI: 10.3390/polym15153181] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 07/21/2023] [Accepted: 07/24/2023] [Indexed: 08/13/2023] Open
Abstract
High-solid-content polystyrene and polyvinyl acetate dispersions of polymer particles with a 50 nm to 500 nm mean particle diameter and 12-55% (w/w) solid content have been produced via emulsion polymerization and characterized regarding their optical and physical properties. Both systems have been analyzed with common particle-size-measuring techniques like dynamic light scattering (DLS) and static light scattering (SLS) and compared to inline particle size distribution (PSD) measurements via photon density wave (PDW) spectroscopy in undiluted samples. It is shown that particle size measurements of undiluted polystyrene dispersions are in good agreement between analysis methods. However, for polyvinyl acetate particles, size determination is challenging due to bound water in the produced polymer. For the first time, water-swelling factors were determined via an iterative approach of PDW spectroscopy error (Χ2) minimization. It is shown that water-swollen particles can be analyzed in high-solid-content solutions and their physical properties can be assumed to determine the refractive index, density, and volume fraction in dispersion. It was found that assumed water swelling improved the reduced scattering coefficient fit by PDW spectroscopy by up to ten times and particle size determination was refined and enabled. Particle size analysis of the water-swollen particles agreed well with offline-based state-of-the-art techniques.
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Affiliation(s)
- Stephanie Schlappa
- Department of Physical Chemistry, innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany (M.M.)
| | - Lena Bressel
- Department of Physical Chemistry, innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany (M.M.)
| | - Oliver Reich
- Knowledge and Technology Transfer, Faculty of Science, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany;
| | - Marvin Münzberg
- Department of Physical Chemistry, innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany (M.M.)
- Knowledge and Technology Transfer, Faculty of Science, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany;
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Salvador D, Acosta Y, Zamora A, Castillo M. Rennet-Induced Casein Micelle Aggregation Models: A Review. Foods 2022; 11:foods11091243. [PMID: 35563966 PMCID: PMC9101341 DOI: 10.3390/foods11091243] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Revised: 04/07/2022] [Accepted: 04/12/2022] [Indexed: 01/27/2023] Open
Abstract
Two phases are generally recognized in the enzymatic coagulation of milk: hydrolysis and aggregation, although nowadays more and more researchers consider the non-enzymatic phase to actually be a stage of gel formation made up of two sub-stages: micellar aggregation and hardening of the three-dimensional network of para-κ-casein. To evaluate this controversy, the main descriptive models have been reviewed. Most of them can only model micellar aggregation, without modeling the hardening stage. Some are not generalizable enough. However, more recent models have been proposed, applicable to a wide range of conditions, which could differentiate both substages. Manufacturing quality enzymatic cheeses in a cost-effective and consistent manner requires effective control of coagulation, which implies studying the non-enzymatic sub-stages of coagulation separately, as numerous studies require specific measurement methods for each of them. Some authors have recently reviewed the micellar aggregation models, but without differentiating it from hardening. Therefore, a review of the proposed models is necessary, as coagulation cannot be controlled without knowing its mechanisms and the stages that constitute it.
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Affiliation(s)
- Daniel Salvador
- Department of Agroindustrial Science, National University of Trujillo, AV. Juan Pablo II s/n—University City, Trujillo 13011, Peru;
| | - Yoseli Acosta
- School of Agroindustrial Engineering, National University of Trujillo, AV. Juan Pablo II s/n—University City, Trujillo 13011, Peru;
| | - Anna Zamora
- Department of Animal and Food Science, Centre d’Innovació, Recerca i Transferència en Tecnologia dels Aliments (CIRTTA), Universitat Autònoma de Barcelona, Travessera dels Turons s/n, Bellaterra, 08193 Barcelona, Spain;
| | - Manuel Castillo
- Department of Animal and Food Science, Centre d’Innovació, Recerca i Transferència en Tecnologia dels Aliments (CIRTTA), Universitat Autònoma de Barcelona, Travessera dels Turons s/n, Bellaterra, 08193 Barcelona, Spain;
- Correspondence: ; Tel.: +34-93-581-1123
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Jacob LI, Pauer W. Scale-up of Emulsion Polymerisation up to 100 L and with a Polymer Content of up to 67 wt%, Monitored by Photon Density Wave Spectroscopy. Polymers (Basel) 2022; 14:polym14081574. [PMID: 35458324 PMCID: PMC9028448 DOI: 10.3390/polym14081574] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 03/14/2022] [Accepted: 04/07/2022] [Indexed: 02/06/2023] Open
Abstract
The scale-up process of the high solid content (up to 67 wt%) emulsion polymerisation of vinyl acetate and Versa®10 from 1 L over 10 L to 100 L was investigated. An emulsion copolymerisation of vinyl acetate and neodecanoic acid vinyl ester in a molar ratio of 9:1 was carried out in a starved-fed semi-batch operation. As a radical source, a redox initiator system consisting of L-ascorbic acid, tert-butyl hydroperoxide and ammonium iron (III) sulphate was used. The process parameters, such as the required stirring speed and heat dissipation, were determined and adjusted beforehand via reaction calorimetry to ensure a successful scale-up without safety issues. In addition, the emulsion polymerisation was monitored inline by Raman (qualitative monomer accumulation), as well as Photon Density Wave spectroscopy (particle size and scattering coefficient) and temperature measurements. The data provided by Raman spectroscopy and temperature measurements revealed mixing difficulties due to an insufficient stirring rate, while the inline measurement with Photon Density Wave spectroscopy offered an insight into the development of the product properties. It proved to be reliable and precise throughout the entire scale-up process, especially compared to conventional offline methods, such as dynamic light scattering or sedimentation analysis by means of a disc centrifuge, both of which encountered issues when using higher polymer contents.
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6
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Sandmann M, Münzberg M, Bressel L, Reich O, Hass R. Inline monitoring of high cell density cultivation of Scenedesmus rubescens in a mesh ultra-thin layer photobioreactor by photon density wave spectroscopy. BMC Res Notes 2022; 15:54. [PMID: 35168633 PMCID: PMC8845379 DOI: 10.1186/s13104-022-05943-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 02/01/2022] [Indexed: 11/30/2022] Open
Abstract
Objective Due to multiple light scattering that occurs inside and between cells, quantitative optical spectroscopy in turbid biological suspensions is still a major challenge. This includes also optical inline determination of biomass in bioprocessing. Photon Density Wave (PDW) spectroscopy, a technique based on multiple light scattering, enables the independent and absolute determination of optical key parameters of concentrated cell suspensions, which allow to determine biomass during cultivation. Results A unique reactor type, called “mesh ultra-thin layer photobioreactor” was used to create a highly concentrated algal suspension. PDW spectroscopy measurements were carried out continuously in the reactor without any need of sampling or sample preparation, over 3 weeks, and with 10-min time resolution. Conventional dry matter content and coulter counter measurements have been employed as established offline reference analysis. The PBR allowed peak cell dry weight (CDW) of 33.4 g L−1. It is shown that the reduced scattering coefficient determined by PDW spectroscopy is strongly correlated with the biomass concentration in suspension and is thus suitable for process understanding. The reactor in combination with the fiber-optical measurement approach will lead to a better process management. Supplementary Information The online version contains supplementary material available at 10.1186/s13104-022-05943-2.
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Jacob LI, Pauer W. In-line monitoring of latex-particle size during emulsion polymerizations with a high polymer content of more than 60. RSC Adv 2020; 10:26528-26534. [PMID: 35519727 PMCID: PMC9055508 DOI: 10.1039/d0ra02523b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 07/04/2020] [Indexed: 11/21/2022] Open
Abstract
The photon density wave (PDW) spectroscopy is established in the fields of biochemistry and food chemistry as an online analytical method for the determination of mean particle sizes. This work examines PDW spectroscopy regarding its potential in high solid content emulsion polymerization. For this reason, emulsion copolymerization with a tendency for agglomeration of vinyl acetate and Versa® 10 in a molar ratio of 9 : 1, and with varying emulsifier content, was carried out in semi-batch operation mode with different target particle sizes from 50 to 325 nm. A redox initiator system, consisting of l-ascorbic acid, tert-butyl hydroperoxide and ammonium iron(iii) sulfate, was used as a radical source. The mean particle sizes of PDW spectroscopy were compared with those of conventional offline measurement methods, such as dynamic light scattering (DLS) and sedimentation analysis, by means of a disc centrifuge. The determined mean particle sizes show a very good reproducibility and agreement between DLS and sedimentation analysis up to a polymer content of 36%, after which measurements were rendered difficult due to agglomeration. Nevertheless, PDW spectroscopy was able to continue providing reproducible measurements until reaching a polymer content of 63%.
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Affiliation(s)
- Laurence Isabelle Jacob
- Institute for Technical and Macromolecular Chemistry, University of Hamburg Bundesstraße 45 20146 Hamburg Germany +49 40 42838 6007
| | - Werner Pauer
- Institute for Technical and Macromolecular Chemistry, University of Hamburg Bundesstraße 45 20146 Hamburg Germany +49 40 42838 6007
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8
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Bressel K, Müller W, Leser ME, Reich O, Hass R, Wooster TJ. Depletion-Induced Flocculation of Concentrated Emulsions Probed by Photon Density Wave Spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:3504-3513. [PMID: 32162925 DOI: 10.1021/acs.langmuir.9b03642] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Stable, creaming-free oil in water emulsions with high volume fractions of oil (ϕ = 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 ϕ = 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 μs' could be identified. First, a rapid, temperature-dependent change in μs' during the depletion process was observed. Second, the further decrease of μs' follows a power law in analogy to a spinodal demixing behavior, as described by the Cahn-Hilliard theory.
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Affiliation(s)
- Katharina Bressel
- Physical Chemistry-InnoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany
| | - Wenke Müller
- Physical Chemistry-InnoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany
| | - Martin E Leser
- Institute of Material Science, Nestlé Research Center, Vers-chez-les-Blanc, 1000 Lausanne, Switzerland
| | - Oliver Reich
- Physical Chemistry-InnoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany
| | - Roland Hass
- Physical Chemistry-InnoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476 Potsdam, Germany
| | - Tim J Wooster
- Institute of Material Science, Nestlé Research Center, Vers-chez-les-Blanc, 1000 Lausanne, Switzerland
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9
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In-Line Monitoring of Polyhydroxyalkanoate (PHA) Production during High-Cell-Density Plant Oil Cultivations Using Photon Density Wave Spectroscopy. Bioengineering (Basel) 2019; 6:bioengineering6030085. [PMID: 31546779 PMCID: PMC6783927 DOI: 10.3390/bioengineering6030085] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 09/12/2019] [Accepted: 09/17/2019] [Indexed: 12/25/2022] Open
Abstract
Polyhydroxyalkanoates (PHAs) are biodegradable plastic-like materials with versatile properties. Plant oils are excellent carbon sources for a cost-effective PHA production, due to their high carbon content, large availability, and comparatively low prices. Additionally, efficient process development and control is required for competitive PHA production, which can be facilitated by on-line or in-line monitoring devices. To this end, we have evaluated photon density wave (PDW) spectroscopy as a new process analytical technology for Ralstonia eutropha (Cupriavidus necator) H16 plant oil cultivations producing polyhydroxybutyrate (PHB) as an intracellular polymer. PDW spectroscopy was used for in-line recording of the reduced scattering coefficient µs’ and the absorption coefficient µa at 638 nm. A correlation of µs’ with the cell dry weight (CDW) and µa with the residual cell dry weight (RCDW) was observed during growth, PHB accumulation, and PHB degradation phases in batch and pulse feed cultivations. The correlation was used to predict CDW, RCDW, and PHB formation in a high-cell-density fed-batch cultivation with a productivity of 1.65 gPHB·L−1·h−1 and a final biomass of 106 g·L−1 containing 73 wt% PHB. The new method applied in this study allows in-line monitoring of CDW, RCDW, and PHA formation.
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10
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Inline characterization of dispersion formation of a solvent-borne acrylic copolymer by Photon Density Wave spectroscopy. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.08.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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11
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Hartwig A, Hass R. Monitoring Lactose Crystallization at Industrially Relevant Concentrations by Photon Density Wave Spectroscopy. Chem Eng Technol 2018. [DOI: 10.1002/ceat.201700685] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Anne Hartwig
- University of Potsdam; Institute of Chemistry; Physical Chemistry - innoFSPEC; Am Muehlenberg 3 14476 Potsdam Germany
| | - Roland Hass
- University of Potsdam; Institute of Chemistry; Physical Chemistry - innoFSPEC; Am Muehlenberg 3 14476 Potsdam Germany
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12
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Werner P, Münzberg M, Hass R, Reich O. Process analytical approaches for the coil-to-globule transition of poly(N-isopropylacrylamide) in a concentrated aqueous suspension. Anal Bioanal Chem 2017; 409:807-819. [PMID: 27830315 PMCID: PMC5233752 DOI: 10.1007/s00216-016-0050-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 10/14/2016] [Accepted: 10/21/2016] [Indexed: 11/30/2022]
Abstract
The coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM) microgel particles suspended in water has been investigated in situ as a function of heating and cooling rate with four optical process analytical technologies (PAT), sensitive to structural changes of the polymer. Photon Density Wave (PDW) spectroscopy, Focused Beam Reflectance Measurements (FBRM), turbidity measurements, and Particle Vision Microscope (PVM) measurements are found to be powerful tools for the monitoring of the temperature-dependent transition of such thermo-responsive polymers. These in-line technologies allow for monitoring of either the reduced scattering coefficient and the absorption coefficient, the chord length distribution, the reflected intensities, or the relative backscatter index via in-process imaging, respectively. Varying heating and cooling rates result in rate-dependent lower critical solution temperatures (LCST), with different impact of cooling and heating. Particularly, the data obtained by PDW spectroscopy can be used to estimate the thermodynamic transition temperature of PNIPAM for infinitesimal heating or cooling rates. In addition, an inverse hysteresis and a reversible building of micrometer-sized agglomerates are observed for the PNIPAM transition process.
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Affiliation(s)
- Peter Werner
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany.
| | - Marvin Münzberg
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
| | - Roland Hass
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
| | - Oliver Reich
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
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13
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Tippmann J, Becker T. Das Zusammenspiel von Verfahrenstechnik und Technologie in der Brauerei. CHEM-ING-TECH 2016. [DOI: 10.1002/cite.201600058] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Münzberg M, Hass R, Dinh Duc Khanh N, Reich O. Limitations of turbidity process probes and formazine as their calibration standard. Anal Bioanal Chem 2016; 409:719-728. [PMID: 27695985 PMCID: PMC5233748 DOI: 10.1007/s00216-016-9893-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 08/11/2016] [Accepted: 08/18/2016] [Indexed: 12/03/2022]
Abstract
Turbidity measurements are frequently implemented for the monitoring of heterogeneous chemical, physical, or biotechnological processes. However, for quantitative measurements, turbidity probes need calibration, as is requested and regulated by the ISO 7027:1999. Accordingly, a formazine suspension has to be produced. Despite this regulatory demand, no scientific publication on the stability and reproducibility of this polymerization process is available. In addition, no characterization of the optical properties of this calibration material with other optical methods had been achieved so far. Thus, in this contribution, process conditions such as temperature and concentration have been systematically investigated by turbidity probe measurements and Photon Density Wave (PDW) spectroscopy, revealing an influence on the temporal formazine formation onset. In contrast, different reaction temperatures do not lead to different scattering properties for the final formazine suspensions, but give an access to the activation energy for this condensation reaction. Based on PDW spectroscopy data, the synthesis of formazine is reproducible. However, very strong influences of the ambient conditions on the measurements of the turbidity probe have been observed, limiting its applicability. The restrictions of the turbidity probe with respect to scatterer concentration are examined on the basis of formazine and polystyrene suspensions. Compared to PDW spectroscopy data, signal saturation is observed at already low reduced scattering coefficients.
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Affiliation(s)
- Marvin Münzberg
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany.
| | - Roland Hass
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
| | - Ninh Dinh Duc Khanh
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
| | - Oliver Reich
- Physical Chemistry - innoFSPEC, University of Potsdam, Am Mühlenberg 3, 14476, Potsdam-Golm, Germany
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