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Goh CF, Lane ME. Advanced structural characterisation of pharmaceuticals using nano-thermal analysis (nano-TA). Adv Drug Deliv Rev 2022; 180:114077. [PMID: 34896130 DOI: 10.1016/j.addr.2021.114077] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/12/2021] [Accepted: 12/02/2021] [Indexed: 12/17/2022]
Abstract
The production of drug delivery systems fabricated at the nano scale comes with the challenges of identifying reliable characterisation tools, especially for solid dosage forms. A full understanding of physicochemical properties of solid-state systems at a high spatial resolution is essential to monitor their manufacturability, processability, performance (dissolution) and stability. Nano-thermal analysis (nano-TA), a hybrid of atomic force microscopy (AFM) and thermal analysis, has emerged as a solution to address the need for complete characterisation of samples with surface heterogeneity. Nano-TA provides not only physical information using conventional AFM but also the thermal behaviour of these systems as an additional chemical dimension. In this review, the principles and techniques of nano-TA are discussed with emphasis on recent pharmaceutical applications. Building on nano-TA, the combination of this approach with infrared spectroscopic analysis is briefly introduced. The challenges and considerations for future development of nano-TA characterisation are also outlined.
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Affiliation(s)
- Choon Fu Goh
- Discipline of Pharmaceutical Technology, School of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia.
| | - Majella E Lane
- Department of Pharmaceutics, UCL School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom.
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2
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Gholizadeh-Hashjin A, Shabani M, Monajjemzadeh F. Evaluation of Pharmaceutical Compatibility between Acarbose and Common Excipients Used in the Development of Controlled Release Formulations. PHARMACEUTICAL SCIENCES 2020. [DOI: 10.34172/ps.2020.67] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Background: Excipients are used in the formulation of pharmaceutical dosage forms, but mayinteract with active pharmaceutical ingredients (APIs). Some of these interactions could alterthe physicochemical properties of the APIs which can affect the therapeutic efficacy and safety.Acarbose is an anti-diabetic drug used in this study as an API to investigate its compatibility withcommon excipients in order to development of pharmaceutical controlled release formulations. Methods: For this purpose, 15 different excipients were selected. Binary mixtures of drug witheach of the excipients (1:1 mass ratio) were prepared. Mixtures were analyzed immediately aftermixing and also after incubation at stress conditions (adding 20% water and incubated at 40°Cfor 2 months). The thermal analytical investigation like differential scanning calorimetry (DSC),Fourier transform infra-red spectroscopy (FTIR) and high-performance liquid chromatography(HPLC) were employed for physicochemical evaluations of the possible incompatibility.Photodiode-array (PDA) and mass studies were performed to ensure the peak purity of theHPLC peaks of API in stressed samples. Results: Incompatible excipients with acarbose were determined as EC (ethyl cellulose),Carbopol 934, Hydroxypropyl cellulose, PEG2000 (Polyethylene Glycol 2000), Mg Stearate, NaAlginate and Poloxamer. Conclusion: Results of this study would be used for the development of controlled releaseformulation of acarbose. It is recommended to avoid the use of incompatible excipients.
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Affiliation(s)
- Aiesheh Gholizadeh-Hashjin
- Department of Pharmaceutical and Food Control, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran
- Student Research Committee, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Mohammad Shabani
- Student Research Committee, Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Farnaz Monajjemzadeh
- Food and Drug Safety Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
- National Institute for Medical Research Development (NIMAD), Tehran, Iran
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3
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Kumar A, Singh P, Nanda A. Hot stage microscopy and its applications in pharmaceutical characterization. Appl Microsc 2020; 50:12. [PMID: 33580349 PMCID: PMC7818341 DOI: 10.1186/s42649-020-00032-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 06/02/2020] [Indexed: 01/27/2023] Open
Abstract
Hot stage microscopy (HSM) is a thermal analysis technique that combines the best properties of thermal analysis and microscopy. HSM is rapidly gaining interest in pharmaceuticals as well as in other fields as a regular characterization technique. In pharmaceuticals HSM is used to support differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA) observations and to detect small changes in the sample that may be missed by DSC and TGA during a thermal experiment. Study of various physical and chemical properties such sample morphology, crystalline nature, polymorphism, desolvation, miscibility, melting, solid state transitions and incompatibility between various pharmaceutical compounds can be carried out using HSM. HSM is also widely used to screen cocrystals, excipients and polymers for solid dispersions. With the advancements in research methodologies, it is now possible to use HSM in conjunction with other characterization techniques such as Fourier transform infrared spectroscopy (FTIR), DSC, Raman spectroscopy, scanning electron microscopy (SEM) which may have additional benefits over traditional characterization techniques for rapid and comprehensive solid state characterization.
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Affiliation(s)
- Arun Kumar
- Department of Pharmaceutical Sciences, Maharshi Dayanand University, Rohtak, Haryana, 124001, India
| | - Pritam Singh
- Department of Pharmaceutical Sciences, Maharshi Dayanand University, Rohtak, Haryana, 124001, India
| | - Arun Nanda
- Department of Pharmaceutical Sciences, Maharshi Dayanand University, Rohtak, Haryana, 124001, India.
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4
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Veronica N, Liew CV, Heng PWS. Insights on the role of excipients and tablet matrix porosity on aspirin stability. Int J Pharm 2020; 580:119218. [PMID: 32165224 DOI: 10.1016/j.ijpharm.2020.119218] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Revised: 03/05/2020] [Accepted: 03/08/2020] [Indexed: 11/28/2022]
Abstract
Excipient-moisture interaction can be a critical attribute in determination of product stability. This study aimed to investigate influence of integrating excipients having different moisture interaction into moisture sensitive drug formulations. Aspirin was formulated with maize starch (MS), microcrystalline cellulose (MCC) and calcium hydrogen phosphate dihydrate (DCP). The excipients were evaluated for their inherent moisture content and water activity. Tablets fabricated at different compression pressures were exposed to 40 °C, 75% relative humidity for a stipulated period before analyzing for aspirin degradation. The results revealed that while MS had higher moisture content, the water activity was relatively low. Consequently, MS tablets had lower aspirin degradation than MCC and DCP tablets. In contrast, high water activity of DCP resulted in greater aspirin degradation. This was despite the low moisture content of DCP. Influence of tablet porosity on aspirin degradation was minimal. This illustrated the fugacity of moisture, possessing high thermodynamic activity and physical spatial delimitation would not suppress its distribution. The findings suggested that excipients possessing high water retentive capacity could potentially be useful as internal tablet desiccants by acting as a moisture scavenger. This study also highlights the importance of water activity in preformulation studies related to the choice of excipients.
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Affiliation(s)
- Natalia Veronica
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Celine Valeria Liew
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore
| | - Paul Wan Sia Heng
- GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
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Goh CF, Moffat JG, Craig DQM, Hadgraft J, Lane ME. Monitoring Drug Crystallization in Percutaneous Penetration Using Localized Nanothermal Analysis and Photothermal Microspectroscopy. Mol Pharm 2018; 16:359-370. [DOI: 10.1021/acs.molpharmaceut.8b01027] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Choon Fu Goh
- Department of Pharmaceutics, UCL School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom
- Discipline of Pharmaceutical Technology, School of Pharmaceutical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
| | - Jonathan G. Moffat
- Asylum Research, Oxford Instruments Company, Halifax Road, HP12 3SE High Wycombe, United Kingdom
| | - Duncan Q. M. Craig
- Department of Pharmaceutics, UCL School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom
| | - Jonathan Hadgraft
- Department of Pharmaceutics, UCL School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom
| | - Majella E. Lane
- Department of Pharmaceutics, UCL School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom
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6
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Kaur R, Sinha VR. Use of thermal and non thermal techniques for assessing compatibility between mirtazapine and solid lipids. J Pharm Biomed Anal 2018; 161:144-158. [PMID: 30149190 DOI: 10.1016/j.jpba.2018.08.041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 08/10/2018] [Accepted: 08/19/2018] [Indexed: 11/26/2022]
Abstract
The present investigation was aimed at the evaluation of possible interactions between mirtazapine and selected solid lipids that are commonly used to develop solid lipid nanoparticles (SLNs) and nanostructured lipidic carriers (NLCs). The solids lipids explored were palmitic acid, stearic acid, glycerylmonostearate, cutina CPPH, sterotex NF, gelucire 50/13, hydrogenated castor oil and compritol 888 ATO. The techniques used were Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Hot Stage Microscopy (HSM) and Isothermal Stress Testing (IST) studies. In some cases, the DSC results indicated the possibility of drug-solid lipid interactions which was further ruled out by performing HSM studies. Moreover, IST studies were also used to further confirm the compatibility between the drug and selected solid lipids. And the findings from these studies indicated compatibility between mirtazapine and solid lipids that can further be used to develop SLNs or NLCs.
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Affiliation(s)
- Randeep Kaur
- University Institute of Pharmaceutical Sciences, UGC-Centre for Advanced Studies, Panjab University, Chandigarh, 160014, India
| | - V R Sinha
- University Institute of Pharmaceutical Sciences, UGC-Centre for Advanced Studies, Panjab University, Chandigarh, 160014, India.
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7
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Formulation and evaluation of selected transmucosal dosage forms containing a double fixed-dose of acyclovir and ketoconazole. Eur J Pharm Sci 2018; 111:503-513. [DOI: 10.1016/j.ejps.2017.10.033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Revised: 09/28/2017] [Accepted: 10/24/2017] [Indexed: 11/22/2022]
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8
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Hoffmann WD, Kertesz V, Srijanto BR, Van Berkel GJ. Atomic Force Microscopy Thermally-Assisted Microsampling with Atmospheric Pressure Temperature Ramped Thermal Desorption/Ionization-Mass Spectrometry Analysis. Anal Chem 2017; 89:3036-3042. [DOI: 10.1021/acs.analchem.6b04733] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- William D. Hoffmann
- Mass
Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Vilmos Kertesz
- Mass
Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Bernadeta R. Srijanto
- Center
for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Gary J. Van Berkel
- Mass
Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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9
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Moffat JG, Eddleston MD, Belton PS, Jones W, Craig DQM. Analysis of single particle photodegradation using photothermal infrared microspectroscopy. Analyst 2013; 138:2315-22. [PMID: 23446375 DOI: 10.1039/c3an36686c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The increasing use of high throughput methods, coupled with the need to develop approaches to anticipate long term stability issues, has necessitated the introduction of testing approaches whereby extremely small samples may be rapidly analysed. A novel method is described whereby the UV light-induced degradation of single particles of a model drug, nifedipine, may be rapidly and simply monitored using photothermal infrared microspectroscopy (PTMS). The technique involves the contact attachment of individual particles to a heated probe tip composed of a modified Wollaston wire which enables temperature fluctuations to be measured. Application of a focused IR beam to excite the sample allows measurement and subsequent Fourier transformation of the resultant interferogram to produce an IR spectrum which is in good agreement with that obtained from conventional IR methods. By application of a UV source to the assembly for specified time periods, we demonstrate that it is possible to monitor the appearance of peaks associated with degradation products as a function of time. The technique is critically evaluated in terms of practical issues associated with volatilization, particle size effects and orientation to the light source as well as more general issues associated with the sensitivity, resolution and quantitative interpretation of data from the PTMS technique. Overall the method has been shown to be capable of rapid measurement of photo-instability on individual particles, with important implications for development of the approach as a rapid screening or high throughput technique, although there are practical and theoretical limitations to reliable quantitative analysis at the present time.
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Affiliation(s)
- Jonathan G Moffat
- University College London School of Pharmacy, 29-39 Brunswick Square, London WC1N 1AX, UK
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Qi S, Moffat JG, Yang Z. Early Stage Phase Separation in Pharmaceutical Solid Dispersion Thin Films under High Humidity: Improved Spatial Understanding Using Probe-Based Thermal and Spectroscopic Nanocharacterization Methods. Mol Pharm 2013; 10:918-30. [DOI: 10.1021/mp300557q] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sheng Qi
- School of Pharmacy, University of East Anglia, Norwich, Norfolk, NR4 7TJ, United Kingdom
| | - Jonathan G. Moffat
- School of Pharmacy, University of East Anglia, Norwich, Norfolk, NR4 7TJ, United Kingdom
| | - Ziyi Yang
- School of Pharmacy, University of East Anglia, Norwich, Norfolk, NR4 7TJ, United Kingdom
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11
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Abstract
Melt extrusion (ME) over recent years has found widespread application as a viable drug delivery option in the drug development process. ME applications include taste masking, solid-state stability enhancement, sustained drug release and solubility enhancement. While ME can result in amorphous or crystalline solid dispersions depending upon several factors, solubility enhancement applications are centered around generating amorphous dispersions, primarily because of the free energy benefits they offer. In line with the purview of the current issue, this review assesses the utility of ME as a means of enhancing solubility of poorly soluble drugs/chemicals. The review describes major processing aspects of ME technology, definition and understanding of the amorphous state, manufacturability, analytical characterization and biopharmaceutical performance testing to better understand the strength and weakness of this formulation strategy for poorly soluble drugs. In addition, this paper highlights the potential advantages of employing a fusion of techniques, including pharmaceutical co-crystals and spray drying/solvent evaporation, facilitating the design of formulations of API exhibiting specific physico-chemical characteristics. Finally, the review presents some successful case studies of commercialized ME based products.
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Affiliation(s)
- Sejal Shah
- Department of Pharmaceutics, Pii Center for Pharmaceutical Technology, School of Pharmacy, The University of Mississippi, University, MS 38677-1848, United States
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12
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Baird JA, Taylor LS. Evaluation of amorphous solid dispersion properties using thermal analysis techniques. Adv Drug Deliv Rev 2012; 64:396-421. [PMID: 21843564 DOI: 10.1016/j.addr.2011.07.009] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 07/25/2011] [Accepted: 07/28/2011] [Indexed: 11/28/2022]
Abstract
Amorphous solid dispersions are an increasingly important formulation approach to improve the dissolution rate and apparent solubility of poorly water soluble compounds. Due to their complex physicochemical properties, there is a need for multi-faceted analytical methods to enable comprehensive characterization, and thermal techniques are widely employed for this purpose. Key parameters of interest that can influence product performance include the glass transition temperature (T(g)), molecular mobility of the drug, miscibility between the drug and excipients, and the rate and extent of drug crystallization. It is important to evaluate the type of information pertaining to the aforementioned properties that can be extracted from thermal analytical measurements, in addition to considering any inherent assumptions or limitations of the various analytical approaches. Although differential scanning calorimetry (DSC) is the most widely used thermal analytical technique applied to the characterization of amorphous solid dispersions, there are many established and emerging techniques which have been shown to provide useful information. Comprehensive characterization of fundamental material descriptors will ultimately lead to the formulation of more robust solid dispersion products.
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Affiliation(s)
- Jared A Baird
- Department of Industrial and Physical Pharmacy, College of Pharmacy, Purdue University, West Lafayette, Indiana 47907, USA
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Cassidy AM, Gardner CE, Auffret T, Aldous B, Jones W. Decoupling the Eeffects of Esurface Chemistry and Humidity on Solid-State Hydrolysis of Aspirin in the Presence of Dicalcium Phosphate Dihydrate. J Pharm Sci 2012; 101:1496-507. [DOI: 10.1002/jps.23038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 11/16/2011] [Accepted: 12/13/2011] [Indexed: 11/08/2022]
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14
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Dai X, Moffat JG, Wood J, Reading M. Thermal scanning probe microscopy in the development of pharmaceuticals. Adv Drug Deliv Rev 2012; 64:449-60. [PMID: 21856345 DOI: 10.1016/j.addr.2011.07.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 06/29/2011] [Accepted: 07/28/2011] [Indexed: 11/30/2022]
Abstract
The ability to characterize the physical and chemical properties of dosage forms is crucial to a more complete understanding of how vehicles for drug delivery behave and therefore how effective they are. Spatially resolved characterization that enables the visualization of properties on the nanoscale is particularly powerful. The usefulness of scanning probe microscopy (SPM) in the field of drug delivery is becoming increasingly well established and the use of thermal probes offers new capabilities thus enabling SPM to provide more and sometimes unique information. One type of measurement enabled by thermal probes is determining transition temperatures by means of local thermal analysis. The ability to identify and characterize materials in this way has found applications in characterizing a wide range of dosage forms. A complimentary thermal probe technique is photothermal infrared microspectroscopy (PTMS). PTMS offers a variety of advantages over more conventional approaches including the ability analyze compacts without the need for thin sections. It is also able to achieve sub-micron spatial resolution. Thermal probe techniques can characterize pharmaceutical dosage forms in terms of their physical properties and their chemical composition.
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Affiliation(s)
- Xuan Dai
- School of Pharmacy, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK.
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Van Eerdenbrugh B, Taylor LS. Application of mid-IR spectroscopy for the characterization of pharmaceutical systems. Int J Pharm 2011; 417:3-16. [DOI: 10.1016/j.ijpharm.2010.12.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 12/02/2010] [Accepted: 12/09/2010] [Indexed: 10/18/2022]
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16
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Qi S, Belton P, Nollenberger K, Gryczke A, Craig DQM. Compositional Analysis of Low Quantities of Phase Separation in Hot-Melt-Extruded Solid Dispersions: A Combined Atomic Force Microscopy, Photothermal Fourier-Transform Infrared Microspectroscopy, and Localised Thermal Analysis Approach. Pharm Res 2011; 28:2311-26. [DOI: 10.1007/s11095-011-0461-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Accepted: 04/26/2011] [Indexed: 11/28/2022]
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17
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Dai X, Moffat JG, Mayes AG, Reading M, Craig DQM, Belton PS, Grandy DB. Thermal Probe Based Analytical Microscopy: Thermal Analysis and Photothermal Fourier-Transform Infrared Microspectroscopy Together with Thermally Assisted Nanosampling Coupled with Capillary Electrophoresis. Anal Chem 2009; 81:6612-9. [DOI: 10.1021/ac9004869] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xuan Dai
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - Jonathan G. Moffat
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - Andrew G. Mayes
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - Mike Reading
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - Duncan Q. M. Craig
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - Peter S. Belton
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
| | - David B. Grandy
- School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, Norfolk NR4 7TJ, U.K., and IPTME, Loughborough University, Loughborough, Leicestershire, LE11 3TU, U.K
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