Paul Dallin - Academia.edu (original) (raw)
Papers by Paul Dallin
Scientific Reports, Aug 18, 2023
Use of e-cigarettes is increasing, alongside an expanding variety of devices and e-liquids. To ma... more Use of e-cigarettes is increasing, alongside an expanding variety of devices and e-liquids. To match this growth and in line with the expanding legal and regulatory requirements applicable to manufacturers of e-cigarettes (e.g. disclosure of list of ingredients and quantities thereof in a product), rapid methods for determining levels of the main e-liquid constituents-namely, propylene glycol (PG), vegetable glycerol (VG), water and nicotine-are needed. We have assessed the ability of near infrared (NIR) spectroscopy, coupled with partial least squares (PLS) regression, to predict the levels of these constituents in e-liquid formulations. Using NIR spectral data from a large set of reference e-liquids incorporating working concentration ranges, flavourings, and other ingredients, linear calibration models were established for PG, VG, water and nicotine (predicted vs theoretical values, all R 2 > 0.995). The performance of these models was then evaluated on commercial e-liquids using NIR and compared to results obtained by gas chromatography (GC). A strong correlation was observed between NIR-predicted values and measured values for PG, VG and nicotine (all R 2 > 0.955). There was less consistency between predicted and GC measured values for water due to the relatively high limit of quantification (LOQ) of the GC method (2.6% w/w) versus the e-liquid content (0-18% w/w). The LOQ of the NIR method for water was 0.6% w/w, suggesting that NIR may be a more accurate method than GC to predict water concentration in e-liquids, especially at low levels (< 2.6% w/w). Collectively, although limitations of the technique have been identified, specifically for e-liquids containing compounds that might interfere with the set calibrations, our findings suggest that NIR combined with PLS regression is a suitable tool for rapid, simultaneous and high-throughput measurement of PG, VG, water and nicotine levels in most commercial e-liquids.
Changes in temperature can significantly affect spectroscopic-based methods for in situ monitorin... more Changes in temperature can significantly affect spectroscopic-based methods for in situ monitoring of processes. As varying temperature is inherent to many processes, associated temperature effects on spectra are unavoidable, which can hinder solute concentration determination. Ultraviolet (UV) and mid-infrared (IR) data were acquired for L-ascorbic acid (LAA) in MeCN/H 2 O (80:20 w/w) at different concentrations and temperatures. For both techniques, global partial least squares (PLS) models for prediction of LAA concentration constructed without preprocessing of the spectra required a high number of latent variables to account for the effects of temperature on the spectra (root mean square error of cross validation (RMSECV) of 0.18 and 0.16 g/100 g solvent, for UV and IR datasets, respectively). The PLS models constructed on the first derivative spectra required fewer latent variables, yielding variable results in accuracy (RMSECV of 0.23 and 0.06 g/100 g solvent, respectively). Corresponding isothermal local models constructed indicated improved model performance that required fewer latent variables in the absence of temperature effects (RMSECV of 0.01 and 0.04 g/100 g solvent, respectively). Temperature correction of the spectral data via loading space standardization (LSS) enabled the construction of global models using the same number of latent variables as the corresponding local model, which exhibited comparable model performance (RMSECV of 0.06 and 0.04 g/100 g solvent, respectively). The additional chemometric effort required for LSS is justified if prediction of solute concentration is required for in situ monitoring and control of cooling crystallization with an accuracy and precision approaching that attainable using an isothermal local model. However, the model performance with minimal preprocessing may be sufficient, for example, in the early phase development of a cooling crystallization process, where high accuracy is not always required. UV and IR spectrometries were used to determine solubility diagrams for LAA in MeCN/H 2 O (80:20 w/w), which were found to be accurate compared to those obtained using the traditional techniques of transmittance and gravimetric measurement. For both UV and IR spectrometries, solubility values obtained from models with LSS temperature correction were in better agreement with those determined gravimetrically. In this first example of the application of LSS to UV spectra, significant improvement in the predicted solute concentration is achieved with the additional chemometric effort. There is no extra experimental burden associated with the use of LSS if a structured approach is employed to acquire calibration data that account for both temperature and concentration.
Raman spectroscopy has been used to provide a rapid, non-invasive and non-destructive quantificat... more Raman spectroscopy has been used to provide a rapid, non-invasive and non-destructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm and 586 cm corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and hence, for maximum parahydrogen production (50 %) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field NMR spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The ...
14 A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of 15 station... more 14 A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of 15 stationary powders and powders mixing at 50 rpm in a high shear convective blender. 16 Two methods of assessing the effect of particle characteristics on the Raman sampling 17 depth for microcrystalline cellulose (Avicel), aspirin or sodium nitrate were compared: (i) 18 the information depth, based on the diminishing Raman signal of TiO2 in a reference 19 plate as the depth of powder prior to the plate was increased, and (ii) the depth at which a 20 sample became infinitely thick, based on the depth of powder at which the Raman signal 21 This is an accepted author manuscript, accepted by Journal of Pharmaceutical and Biomedical Analysis, 04 December 2012. 2 of the compound became constant. The particle size, shape, density and/or light 22 absorption capability of the compounds were shown to affect the “information” and 23 “infinitely thick” depths of individual compounds. However, when differen...
Strathprints is designed to allow users to access the research output of the University of Strath... more Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.
Applied Spectroscopy, 2018
Raman spectroscopy has been used to provide a rapid, noninvasive, and nondestructive quantificati... more Raman spectroscopy has been used to provide a rapid, noninvasive, and nondestructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm À1 and 586 cm À1 corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and, hence, for maximum parahydrogen production (50%) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field nuclear magnetic resonance (NMR) spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The Raman method does not require a reference sample, as both spin isomers (ortho and para) of hydrogen can be directly detected, which simplifies the procedure and eliminates some sources of error. In the second example, the method was used to monitor the fast conversion of parahydrogen to orthohydrogen in situ. Here the ability to acquire Raman spectra every 30 s enabled a conversion process with a rate constant of 27:4 Â 10 À4 s À1 to be monitored. The Raman method described here represents an improvement on previously reported work, in that it can be easily applied on-line and is approximately 500 times faster. This offers the potential of an industrially compatible method for determining parahydrogen content in applications that require the storage and usage of hydrogen.
Journal of the American Chemical Society, 2011
![Research paper thumbnail of Inelastic neutron scattering study of hydride ligands in [(μ2-H)2Os3(CO)10]: Evidence for a direct HH interaction](https://attachments.academia-assets.com/86067021/thumbnails/1.jpg)
](Polyhedron, 1990
The inelastic neutron scattering (INS) spectrum of [(~2-H)20~3(C0)1,,] has been recorded ; bands ... more The inelastic neutron scattering (INS) spectrum of [(~2-H)20~3(C0)1,,] has been recorded ; bands due to M-H vibrations are clearly seen and evidence has been found for a direct interaction between the two hydrogen ligands.
Physical Chemistry Chemical Physics, 1999
ABSTRACT
Journal of Pharmaceutical and Biomedical Analysis, 2013
A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of stationary po... more A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of stationary powders and powders mixing at 50 rpm in a high shear convective blender. Two methods of assessing the effect of particle characteristics on the Raman sampling depth for microcrystalline cellulose (Avicel), aspirin or sodium nitrate were compared: (i) the information depth, based on the diminishing Raman signal of TiO 2 in a reference plate as the depth of powder prior to the plate was increased, and (ii) the depth at which a sample became infinitely thick, based on the depth of powder at which the Raman signal
The Journal of Chemical Physics, 2003
... John A. Stride, Paul H. Dallin, Upali A. Jayasooriya. Abstract. ... The fact that sulfur is a... more ... John A. Stride, Paul H. Dallin, Upali A. Jayasooriya. Abstract. ... The fact that sulfur is a well-documented electron acceptor and that usually acts as a Lewis acid in chemical bonding mechanisms provides an interaction scenario in which the chlorine atoms act as soft Lewis bases. ...
Hyperfine Interactions, 1991
Chemical Engineering Science, 2013
Applied Spectroscopy, 2010
Analytical Chemistry, 2012
383 tablets of a pharmaceutical product were analysed by backscatter and transmission Raman spect... more 383 tablets of a pharmaceutical product were analysed by backscatter and transmission Raman spectrometry to determine the concentration of an active pharmaceutical ingredient (API), chlorpheniramine maleate, at the 2% m/m (4 mg) level. As the exact composition of the tablets was unknown, external calibration samples were prepared from chlorpheniramine maleate and microcrystalline cellulose (Avicel) of different particle size. The API peak at 1594 cm-1 in the 2 nd derivative Raman spectra was used to generate linear calibration models. The API concentration predicted using backscatter Raman measurements was relatively insensitive to the particle size of Avicel. With transmission, however, particle size effects were greater and accurate prediction of the API content was only possible when the photon propagation properties of the calibration and sample tablets were matched. Good agreement was obtained with HPLC analysis when matched calibration tablets were used for both modes. When the calibration and sample tablets are not chemically matched, spectral normalisation based 2 on calculation of relative intensities cannot be used to reduce the effects of differences in physical properties. The main conclusion is that although better for whole tablet analysis, transmission Raman is more sensitive to differences in the photon propagation properties of the calibration and sample tablets.
Analytical Chemistry, 2012
Spectroscopy Europe, 2003
... References 1. J. Andrews and P. Dallin, Spectrosc. Europe 15(3), 2729 (2003). 2. IRLewis and... more ... References 1. J. Andrews and P. Dallin, Spectrosc. Europe 15(3), 2729 (2003). 2. IRLewis and HGM Edwards (Eds), Handbook of Raman Spectroscopy: From the Research Laboratory to the Process Line. Marcel Dekker, New York (2001). ...
Spectroscopy Europe, 2003
... Column John Andrews and Paul Dallin Clairet Scientific Ltd, 17 Scirocco Close, Moulton Park I... more ... Column John Andrews and Paul Dallin Clairet Scientific Ltd, 17 Scirocco Close, Moulton Park Industrial Estate, Northampton, NN6 9JF. E-mail: john.andrews@clairet.co.uk ... 2. AOCS Procedure Cd 1e-01. 3. IR Lewis and HGM Edwards (Eds), Handbook of Raman Spectroscopy. ...
Crystal Growth & Design, 2009
The in situ measurement of solution supersaturation associated with the batch cooling crystalliza... more The in situ measurement of solution supersaturation associated with the batch cooling crystallization of L-glutamic acid (LGA) at 500 mL and 20 L scale sizes is assessed via ATR-FTIR spectroscopy. A partial least squares chemometric calibration model was developed for the online prediction of LGA concentration from measured FTIR absorbance spectra overcoming some significant challenges related to the low sensitivity of LGA in the mid-IR frequency range, its low solubility in water, and its complex speciation chemistry. The solubility data of LGA in water over the temperature range from 40 to 80°C, using ATR-FTIR, reveals excellent agreement with those obtained both from using a gravimetric method and literature data. The metastable zone width determined using the turbidimetric methods as a function of heating/cooling rates and solute concentration is found to increase with increasing cooling rate while it decreases with increasing solution concentration. Monitoring online crystallization via both spontaneous and seeded in 500 mL and 20 L crystallizers reveals good concentration predictions for seeded crystallization, while fouling of the ATR crystal prevents its routine use for unseeded crystallization studies. Higher supersaturation levels are found for the larger crystallizer scale-size consistent with enhancement of secondary nucleation at the smaller scale-size.
Scientific Reports, Aug 18, 2023
Use of e-cigarettes is increasing, alongside an expanding variety of devices and e-liquids. To ma... more Use of e-cigarettes is increasing, alongside an expanding variety of devices and e-liquids. To match this growth and in line with the expanding legal and regulatory requirements applicable to manufacturers of e-cigarettes (e.g. disclosure of list of ingredients and quantities thereof in a product), rapid methods for determining levels of the main e-liquid constituents-namely, propylene glycol (PG), vegetable glycerol (VG), water and nicotine-are needed. We have assessed the ability of near infrared (NIR) spectroscopy, coupled with partial least squares (PLS) regression, to predict the levels of these constituents in e-liquid formulations. Using NIR spectral data from a large set of reference e-liquids incorporating working concentration ranges, flavourings, and other ingredients, linear calibration models were established for PG, VG, water and nicotine (predicted vs theoretical values, all R 2 > 0.995). The performance of these models was then evaluated on commercial e-liquids using NIR and compared to results obtained by gas chromatography (GC). A strong correlation was observed between NIR-predicted values and measured values for PG, VG and nicotine (all R 2 > 0.955). There was less consistency between predicted and GC measured values for water due to the relatively high limit of quantification (LOQ) of the GC method (2.6% w/w) versus the e-liquid content (0-18% w/w). The LOQ of the NIR method for water was 0.6% w/w, suggesting that NIR may be a more accurate method than GC to predict water concentration in e-liquids, especially at low levels (< 2.6% w/w). Collectively, although limitations of the technique have been identified, specifically for e-liquids containing compounds that might interfere with the set calibrations, our findings suggest that NIR combined with PLS regression is a suitable tool for rapid, simultaneous and high-throughput measurement of PG, VG, water and nicotine levels in most commercial e-liquids.
Changes in temperature can significantly affect spectroscopic-based methods for in situ monitorin... more Changes in temperature can significantly affect spectroscopic-based methods for in situ monitoring of processes. As varying temperature is inherent to many processes, associated temperature effects on spectra are unavoidable, which can hinder solute concentration determination. Ultraviolet (UV) and mid-infrared (IR) data were acquired for L-ascorbic acid (LAA) in MeCN/H 2 O (80:20 w/w) at different concentrations and temperatures. For both techniques, global partial least squares (PLS) models for prediction of LAA concentration constructed without preprocessing of the spectra required a high number of latent variables to account for the effects of temperature on the spectra (root mean square error of cross validation (RMSECV) of 0.18 and 0.16 g/100 g solvent, for UV and IR datasets, respectively). The PLS models constructed on the first derivative spectra required fewer latent variables, yielding variable results in accuracy (RMSECV of 0.23 and 0.06 g/100 g solvent, respectively). Corresponding isothermal local models constructed indicated improved model performance that required fewer latent variables in the absence of temperature effects (RMSECV of 0.01 and 0.04 g/100 g solvent, respectively). Temperature correction of the spectral data via loading space standardization (LSS) enabled the construction of global models using the same number of latent variables as the corresponding local model, which exhibited comparable model performance (RMSECV of 0.06 and 0.04 g/100 g solvent, respectively). The additional chemometric effort required for LSS is justified if prediction of solute concentration is required for in situ monitoring and control of cooling crystallization with an accuracy and precision approaching that attainable using an isothermal local model. However, the model performance with minimal preprocessing may be sufficient, for example, in the early phase development of a cooling crystallization process, where high accuracy is not always required. UV and IR spectrometries were used to determine solubility diagrams for LAA in MeCN/H 2 O (80:20 w/w), which were found to be accurate compared to those obtained using the traditional techniques of transmittance and gravimetric measurement. For both UV and IR spectrometries, solubility values obtained from models with LSS temperature correction were in better agreement with those determined gravimetrically. In this first example of the application of LSS to UV spectra, significant improvement in the predicted solute concentration is achieved with the additional chemometric effort. There is no extra experimental burden associated with the use of LSS if a structured approach is employed to acquire calibration data that account for both temperature and concentration.
Raman spectroscopy has been used to provide a rapid, non-invasive and non-destructive quantificat... more Raman spectroscopy has been used to provide a rapid, non-invasive and non-destructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm and 586 cm corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and hence, for maximum parahydrogen production (50 %) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field NMR spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The ...
14 A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of 15 station... more 14 A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of 15 stationary powders and powders mixing at 50 rpm in a high shear convective blender. 16 Two methods of assessing the effect of particle characteristics on the Raman sampling 17 depth for microcrystalline cellulose (Avicel), aspirin or sodium nitrate were compared: (i) 18 the information depth, based on the diminishing Raman signal of TiO2 in a reference 19 plate as the depth of powder prior to the plate was increased, and (ii) the depth at which a 20 sample became infinitely thick, based on the depth of powder at which the Raman signal 21 This is an accepted author manuscript, accepted by Journal of Pharmaceutical and Biomedical Analysis, 04 December 2012. 2 of the compound became constant. The particle size, shape, density and/or light 22 absorption capability of the compounds were shown to affect the “information” and 23 “infinitely thick” depths of individual compounds. However, when differen...
Strathprints is designed to allow users to access the research output of the University of Strath... more Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.
Applied Spectroscopy, 2018
Raman spectroscopy has been used to provide a rapid, noninvasive, and nondestructive quantificati... more Raman spectroscopy has been used to provide a rapid, noninvasive, and nondestructive quantification method for determining the parahydrogen fraction of hydrogen gas. The basis of the method is the measurement of the ratio of the first two rotational bands of hydrogen at 355 cm À1 and 586 cm À1 corresponding to parahydrogen and orthohydrogen, respectively. The method has been used to determine the parahydrogen content during a production process and a reaction. In the first example, the performance of an in-house liquid nitrogen cooled parahydrogen generator was monitored both at-line and on-line. The Raman measurements showed that it took several hours for the generator to reach steady state and, hence, for maximum parahydrogen production (50%) to be reached. The results obtained using Raman spectroscopy were compared to those obtained by at-line low-field nuclear magnetic resonance (NMR) spectroscopy. While the results were in good agreement, Raman analysis has several advantages over NMR for this application. The Raman method does not require a reference sample, as both spin isomers (ortho and para) of hydrogen can be directly detected, which simplifies the procedure and eliminates some sources of error. In the second example, the method was used to monitor the fast conversion of parahydrogen to orthohydrogen in situ. Here the ability to acquire Raman spectra every 30 s enabled a conversion process with a rate constant of 27:4 Â 10 À4 s À1 to be monitored. The Raman method described here represents an improvement on previously reported work, in that it can be easily applied on-line and is approximately 500 times faster. This offers the potential of an industrially compatible method for determining parahydrogen content in applications that require the storage and usage of hydrogen.
Journal of the American Chemical Society, 2011
Polyhedron, 1990
The inelastic neutron scattering (INS) spectrum of [(~2-H)20~3(C0)1,,] has been recorded ; bands ... more The inelastic neutron scattering (INS) spectrum of [(~2-H)20~3(C0)1,,] has been recorded ; bands due to M-H vibrations are clearly seen and evidence has been found for a direct interaction between the two hydrogen ligands.
Physical Chemistry Chemical Physics, 1999
ABSTRACT
Journal of Pharmaceutical and Biomedical Analysis, 2013
A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of stationary po... more A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of stationary powders and powders mixing at 50 rpm in a high shear convective blender. Two methods of assessing the effect of particle characteristics on the Raman sampling depth for microcrystalline cellulose (Avicel), aspirin or sodium nitrate were compared: (i) the information depth, based on the diminishing Raman signal of TiO 2 in a reference plate as the depth of powder prior to the plate was increased, and (ii) the depth at which a sample became infinitely thick, based on the depth of powder at which the Raman signal
The Journal of Chemical Physics, 2003
... John A. Stride, Paul H. Dallin, Upali A. Jayasooriya. Abstract. ... The fact that sulfur is a... more ... John A. Stride, Paul H. Dallin, Upali A. Jayasooriya. Abstract. ... The fact that sulfur is a well-documented electron acceptor and that usually acts as a Lewis acid in chemical bonding mechanisms provides an interaction scenario in which the chlorine atoms act as soft Lewis bases. ...
Hyperfine Interactions, 1991
Chemical Engineering Science, 2013
Applied Spectroscopy, 2010
Analytical Chemistry, 2012
383 tablets of a pharmaceutical product were analysed by backscatter and transmission Raman spect... more 383 tablets of a pharmaceutical product were analysed by backscatter and transmission Raman spectrometry to determine the concentration of an active pharmaceutical ingredient (API), chlorpheniramine maleate, at the 2% m/m (4 mg) level. As the exact composition of the tablets was unknown, external calibration samples were prepared from chlorpheniramine maleate and microcrystalline cellulose (Avicel) of different particle size. The API peak at 1594 cm-1 in the 2 nd derivative Raman spectra was used to generate linear calibration models. The API concentration predicted using backscatter Raman measurements was relatively insensitive to the particle size of Avicel. With transmission, however, particle size effects were greater and accurate prediction of the API content was only possible when the photon propagation properties of the calibration and sample tablets were matched. Good agreement was obtained with HPLC analysis when matched calibration tablets were used for both modes. When the calibration and sample tablets are not chemically matched, spectral normalisation based 2 on calculation of relative intensities cannot be used to reduce the effects of differences in physical properties. The main conclusion is that although better for whole tablet analysis, transmission Raman is more sensitive to differences in the photon propagation properties of the calibration and sample tablets.
Analytical Chemistry, 2012
Spectroscopy Europe, 2003
... References 1. J. Andrews and P. Dallin, Spectrosc. Europe 15(3), 2729 (2003). 2. IRLewis and... more ... References 1. J. Andrews and P. Dallin, Spectrosc. Europe 15(3), 2729 (2003). 2. IRLewis and HGM Edwards (Eds), Handbook of Raman Spectroscopy: From the Research Laboratory to the Process Line. Marcel Dekker, New York (2001). ...
Spectroscopy Europe, 2003
... Column John Andrews and Paul Dallin Clairet Scientific Ltd, 17 Scirocco Close, Moulton Park I... more ... Column John Andrews and Paul Dallin Clairet Scientific Ltd, 17 Scirocco Close, Moulton Park Industrial Estate, Northampton, NN6 9JF. E-mail: john.andrews@clairet.co.uk ... 2. AOCS Procedure Cd 1e-01. 3. IR Lewis and HGM Edwards (Eds), Handbook of Raman Spectroscopy. ...
Crystal Growth & Design, 2009
The in situ measurement of solution supersaturation associated with the batch cooling crystalliza... more The in situ measurement of solution supersaturation associated with the batch cooling crystallization of L-glutamic acid (LGA) at 500 mL and 20 L scale sizes is assessed via ATR-FTIR spectroscopy. A partial least squares chemometric calibration model was developed for the online prediction of LGA concentration from measured FTIR absorbance spectra overcoming some significant challenges related to the low sensitivity of LGA in the mid-IR frequency range, its low solubility in water, and its complex speciation chemistry. The solubility data of LGA in water over the temperature range from 40 to 80°C, using ATR-FTIR, reveals excellent agreement with those obtained both from using a gravimetric method and literature data. The metastable zone width determined using the turbidimetric methods as a function of heating/cooling rates and solute concentration is found to increase with increasing cooling rate while it decreases with increasing solution concentration. Monitoring online crystallization via both spontaneous and seeded in 500 mL and 20 L crystallizers reveals good concentration predictions for seeded crystallization, while fouling of the ATR crystal prevents its routine use for unseeded crystallization studies. Higher supersaturation levels are found for the larger crystallizer scale-size consistent with enhancement of secondary nucleation at the smaller scale-size.