A New Frontier for Nondestructive Spatial Analysis of Pharmaceutical Solid Dosage Forms: Spatially Offset Low-Frequency Raman Spectroscopy

Bērziņš, Kārlis; Fraser‐Miller, Sara J.; Gordon, Keith C.

doi:10.1021/acs.analchem.0c04960

Cited by 19 publications

(14 citation statements)

References 37 publications

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“…Raman spectroscopy is a powerful tool to determine the molecular structure, molecular conformation, intermolecular interactions, and molecular packing pattern, all of which are strongly related to the short-range orders of organic molecules. Low-frequency Raman spectra (LFRS, #300 cm À1 ) can be used to distinguish different polymorphs of organic molecules, [5][6][7][8] as Raman peaks below 300 cm À1 are phonon modes contributed to the unit cell motions (lattice vibrational frequencies). 9 And midfrequency Raman spectra (MFRS, 300-1800 cm À1 ) can provide information about the short-range orders of organic molecules both in solutions and solid states.…”

Section: Introductionmentioning

confidence: 99%

Explanation for the selective crystallization from inosine solutions using mid-frequency Raman difference spectra analysis

et al. 2022

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Section: Introductionmentioning

confidence: 99%

Explanation for the selective crystallization from inosine solutions using mid-frequency Raman difference spectra analysis

et al. 2022

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“… 18 This can be mainly attributed to the removal of the undesirable Rayleigh scattering signal in the low-frequency region. 31 The result suggests the importance of selecting an appropriate wavenumber range.…”

Section: Resultsmentioning

confidence: 99%

Dual-Principal Component Analysis of the Raman Spectrum Matrix to Automatically Identify and Visualize Microplastics and Nanoplastics

et al. 2022

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As emerging contaminants, microplastics are challenging to characterize, particularly when their size is at the nanoscale. While imaging technology has received increasing attention recently, such as Raman imaging, decoding the scanning spectrum matrix can be difficult to achieve result digitally and automatically via software and usually requires the involvement of personal experience and expertise. Herewith, we show a dual-principal component analysis (PCA) approach, where (i) the first round of PCA analysis focuses on the raw spectrum data from the Raman scanning matrix and generates two new matrices, with one containing the spectrum profile to yield the PCA spectrum and the other containing the PCA intensity to be mapped as an image; (ii) the second round of PCA analysis merges the spectrum from the first round of PCA with the standard spectra of eight common plastics, to generate a correlation matrix. From the correlation value, we can digitally assign the principal components from the first round of PCA analysis to the plastics toward imaging, akin to dataset indexing. We also demonstrate the effect of the data pretreatment and the wavenumber variations. Overall, this dual-PCA approach paves the way for machine learning to analyze microplastics and particularly nanoplastics.

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“…To minimize this effect in the future, the focal point of the measurement should be deep within the sample rather than near the cuvette interface. Some avenues to explore to minimize this effect include transmission low-frequency Raman 20 , 35 or spatially offset low-frequency Raman 36 setups, which also have the advantage of probing larger sample volumes.…”

Section: Resultsmentioning

confidence: 99%

Low- versus Mid-frequency Raman Spectroscopy for in Situ Analysis of Crystallization in Slurries

et al. 2022

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Slurry studies are useful for exhaustive polymorph and solid-state stability screening of drug compounds. Raman spectroscopy is convenient for monitoring crystallization in such slurries, as the measurements can be performed in situ even in aqueous environments. While the mid-frequency region (400–4000 cm –1 ) is dominated by intramolecular vibrations and has traditionally been used for such studies, the low-frequency spectral region (<200 cm –1 ) probes solid-state related lattice vibrations and is potentially more valuable for understanding subtle and/or complex crystallization behavior. The aim of the study was to investigate low-frequency Raman spectroscopy for in situ monitoring of crystallization of an amorphous pharmaceutical in slurries for the first time and directly compare the results with those simultaneously obtained with mid-frequency Raman spectroscopy. Amorphous indomethacin (IND) slurries were prepared at pH 1.2 and continuously monitored in situ at 5 and 25 °C with both low- and mid-frequency Raman spectroscopy. At 25 °C, both spectral regions profiled amorphous IND in slurries as converting directly from the amorphous form toward the α crystalline form. In contrast, at 5 °C, principal component analysis revealed a divergence in the detected conversion profiles: the mid-frequency Raman suggested a direct conversion to the α crystalline form, but the low-frequency region showed additional transition points. These were attributed to the appearance of minor amounts of the ε-form. The additional solid-state sensitivity of the low-frequency region was attributed to the better signal-to-noise ratio and more consistent spectra in this region. Finally, the low-frequency Raman spectrum of the ε-form of IND is reported for the first time.

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A New Frontier for Nondestructive Spatial Analysis of Pharmaceutical Solid Dosage Forms: Spatially Offset Low-Frequency Raman Spectroscopy

Cited by 19 publications

References 37 publications

Explanation for the selective crystallization from inosine solutions using mid-frequency Raman difference spectra analysis

Explanation for the selective crystallization from inosine solutions using mid-frequency Raman difference spectra analysis

Dual-Principal Component Analysis of the Raman Spectrum Matrix to Automatically Identify and Visualize Microplastics and Nanoplastics

Low- versus Mid-frequency Raman Spectroscopy for in Situ Analysis of Crystallization in Slurries

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