Application of mid-IR spectroscopy for the characterization of pharmaceutical systems

An evaluation of resolution, accuracy, and precision in FT-IR spectroscopy

Infrared spectroscopy is a foundational technique for the elucidation of chemical structures. The advancements in interferometric spectroscopy, and specifically the development of Fourier transform infrared (FT-IR) spectroscopy, are responsible for the widespread usage of IR spectrometers ranging from teaching labs to pharmaceutical quality control. FT-IR affords an excellent signal-to-noise ratio that permits sensitive sampling with quantitative accuracy and high wavenumber precision based on well documented advantages (Jacquinot, Fellgett, Connes). However, the effect of resolution and instrument-to-instrument variation on wavenumber accuracy is not well understood, with previous work grossly overestimating error. Here, a recommendation of wavenumber accuracy as a function of spectral resolution, accounting for instrument variation among leading manufacturers, is given based on an experimental study of polystyrene and acetaminophen. For peaks that are well resolved and not saturated, the position can be known within 1.1 cm-1 at a spectral resolution of 4 cm-1 or higher, and within 2.2 cm-1 at 8 cm-1 resolution. Other sources of variation are also discussed (e.g., poorly resolved peaks, peak saturation, water interference, spectral noise) to give general recommendations on when IR peak positions can be considered significantly different. Such guidelines are critical for interpreting subtle positional variations, as are often present in different crystal forms of pharmaceuticals.

A Novel Low-Frequency Electromagnetic Active Inertial Sensor for Drug Detection

The purpose of this paper is to demonstrate a new discovery regarding the interaction between materials and very low radio frequencies. Specifically, we observed a feedback response on an inertia active sensor when specific frequencies (around 2-4 kHz) are used to irradiate targeted pharmaceutical samples like aspirin or paracetamol drugs. The characteristics of this phenomenon, such as excitation and relaxation time, the relation between deceleration and a material's quantity, and signal amplitude, are presented and analyzed. Although the underlying physics of this phenomenon is not yet known, we have shown that it has potential applications in remote identification of compounds, detection, and location sensing, as well as identifying substances that exist in plants without the need for any processing. This method is fast, accurate, low-cost, non-destructive, and non-invasive, making it a valuable area for further research that could yield spectacular results in the future.

Real-Time Monitoring of Multistep Batch and Flow Synthesis Processes of a Key Intermediate of Lifitegrast by a Combined Spectrometer System with Both Near-Infrared and Raman Spectroscopies Coupled to Partial Least-Squares

Process analytical technology (PAT) has been successfully applied in numerous chemical synthesis cases and is an important tool in pharmaceutical process research and development. PAT brings new methods and opportunities for the real-time monitoring of chemical processes. In multistep synthesis, real-time monitoring of the complex reaction mixtures is a significant challenge but provides an opportunity to enhance reaction understanding and control. In this study, a combined multichannel spectrometer system with both near-infrared and Raman spectroscopy was built, and calibration models were developed to quantify the desired products, intermediates, and impurities in real-time at multiple points along the synthetic pathway. The capabilities of the system have been demonstrated by operating dynamic experiments in both batch and continuous-flow processes. It represents a significant step forward in data-driven, multistep pharmaceutical ingredient synthesis.

High-performance plasmonic mid-infrared bandpass filters by inverse design

Plasmonic spectral filters composed of periodic nanostructured metal films offer novel opportunities for the development of multispectral imaging technologies in the mid-infrared region. However, traditional plasmonic filters, which typically feature simplistic structures such as nanoholes or nanorings, are constrained by a narrow bandpass and significant crosstalk, leading to limited practical performance. Filters designed using inverse techniques allow a substantial degree of freedom in creating intricate structures that align with desired spectral characteristics, including a quasi-square spectral profile, high transmission, wide full width at half maximum, and reduced crosstalk. In this study, we have utilized an inverse design algorithm to engineer high-performance bandpass filters for the mid-infrared range, achieving an average transmittance exceeding 80% within the bandpass window and below 10% in the stop band, which is comparable to that of commercial multilayer Bragg filters. Nanofabrication processes were employed to transfer the designed pattern into the gold film on ZnS substrate that is transparent in the mid-infrared range. The resulting filters exhibit spectral performance analogous to that of the inversely designed models, making them suitable for direct integration with mid-infrared photodetector arrays in multispectral imaging systems.

Simple and User-Friendly Methodology for Crystal Water Determination by Quantitative Proton NMR Spectroscopy in Deuterium Oxide

In drug research and development, knowledge of the precise structure of an active ingredient is crucial. However, it is equally important to know the water content of the drug molecule, particularly the number of crystal waters present in its structure. Such knowledge ensures the avoidance of drug dosage and formulation errors since the number of water molecules affects the physicochemical and pharmaceutical properties of the molecule. Several methods have been used for crystal water measurements of organic compounds, of which thermogravimetry and crystallography may be the most common ones. To the best of our knowledge, solution-state NMR spectroscopy has not been used for crystal water determination in deuterium oxide. Quantitative NMR (qNMR) method will be presented in the paper with a comparison of single-crystal X-ray diffraction and thermogravimetric analysis results. The qNMR method for water content measurement is straightforward, reproducible, and accurate, including measurement of 1H NMR spectrum before and after the addition of the analyte compound, and the result can be calculated after integration of the reference compound, analyte, and HDO signals using the given equation. In practical terms, there is no need for weighing the samples under study, which makes it simple and is a clear advantage to the current determination methods. In addition, the crystal structures of two model bisphosphonates used herein are reported: that of monopotassium etidronate dihydrate and monosodium zoledronate trihydrate.

Crystallinity: A Complex Critical Quality Attribute of Amorphous Solid Dispersions

Does the performance of an amorphous solid dispersion rely on having 100% amorphous content? What specifications are appropriate for crystalline content within an amorphous solid dispersion (ASD) drug product? In this Perspective, the origin and significance of crystallinity within amorphous solid dispersions will be considered. Crystallinity can be found within an ASD from one of two pathways: (1) incomplete amorphization, or (2) crystal creation (nucleation and crystal growth). While nucleation and crystal growth is the more commonly considered pathway, where crystals originate as a physical stability failure upon accelerated or prolonged storage, manufacturing-based origins of crystallinity are possible as well. Detecting trace levels of crystallinity is a significant analytical challenge, and orthogonal methods should be employed to develop a holistic assessment of sample properties. Probing the impact of crystallinity on release performance which may translate to meaningful clinical significance is inherently challenging, requiring optimization of dissolution test variables to address the complexity of ASD formulations, in terms of drug physicochemical properties (e.g., crystallization tendency), level of crystallinity, crystal reference material selection, and formulation characteristics. The complexity of risk presented by crystallinity to product performance will be illuminated through several case studies, highlighting that a one-size-fits-all approach cannot be used to set specification limits, as the risk of crystallinity can vary widely based on a multitude of factors. Risk assessment considerations surrounding drug physicochemical properties, formulation fundamentals, physical stability, dissolution, and crystal micromeritic properties will be discussed.

Application of an AI image analysis and classification approach to characterise dissolution and precipitation events in the flow through apparatus

Imaging and artificial intelligence (AI) approaches have been used with increasing frequency in pharmaceutical industry in recent years. Characterisation of processes such as drug dissolution and precipitation is vital in quality control testing and drug manufacture. To support existing techniques like in vitro dissolution testing, novel process analytical technologies (PATs) can give an insight into these processes. The aim of this study was to create and explore the potential of an automated image classification model based on image analysis to identify events (dissolution and precipitation) occurring in the flow-through apparatus (FTA) test cell, and the ability to characterise a dissolution process over time. Several precipitation conditions were tested in a USP 4 FTA test cell with images recorded during early (plume formation) and late (particulate re-formation) stages of precipitation. An available MATLAB code was used as a base to develop and validate an anomaly classification model able to detect different events occurring during the precipitation process in the dissolution cell. Two variants of the model were tested on images from a dissolution test in the FTA, with a view to application of the image analysis system to quantitative characterization of the dissolution process over time. It was found that the classification model is highly accurate (>90%) in detecting events occurring in the FTA test cell. The model showed potential to be used to characterise the stages of dissolution and precipitation processes, and as a proof of concept demonstrates potential for deep machine learning image analysis to be applied to kinetics of other pharmaceutical processes.

Coaxial Dielectric Spectroscopy as an In-Line Process Analytical Technique for Reaction Monitoring

The suitability of broadband dielectric spectroscopy (DS) as a tool for in-line (in situ) reaction monitoring is demonstrated. Using the esterification of 4-nitrophenol as a test-case, we show that multivariate analysis of time-resolved DS data-collected across a wide frequency range with a coaxial dip-probe-allows reaction progress to be measured with both high precision and high accuracy. In addition to the workflows for data collection and analysis, we also establish a convenient method for rapidly assessing the applicability of DS to previously untested reactions or processes. We envisage that, given its orthogonality to other spectroscopic methods, its low cost, and its ease of implementation, DS will be a valuable addition to the process chemist's analytical toolbox.

Characterization of Pharmaceutical Tablets by X-ray Tomography

Solid dosage forms such as tablets are extensively used in drug administration for their simplicity and large-scale manufacturing capabilities. High-resolution X-ray tomography is one of the most valuable non-destructive techniques to investigate the internal structure of the tablets for drug product development as well as for a cost effective production process. In this work, we review the recent developments in high-resolution X-ray microtomography and its application towards different tablet characterizations. The increased availability of powerful laboratory instrumentation, as well as the advent of high brilliance and coherent 3rd generation synchrotron light sources, combined with advanced data processing techniques, are driving the application of X-ray microtomography forward as an indispensable tool in the pharmaceutical industry.

Future of computational molecular spectroscopy-from supporting interpretation to leading the innovation

Molecular spectroscopy measures transitions between discrete molecular energies which follow quantum mechanics. Structural information of a molecule is encoded in the spectra, which can be only decoded using quantum mechanics and therefore computational molecular spectroscopy becomes essential. In this review perspective, the role evolution of computational molecular spectroscopy has been discussed with several joint theory and experiment spectroscopic studies in the past decades, which includes rotational (microwave), vibrational and electronic spectroscopy (valence and core) of molecules. With the development in high resolution and computerized synchrotron sourced spectroscopy, spectral measurements and computational molecular spectroscopy need to be integrated for materials development. Contemporary computational molecular spectroscopy is, therefore, more than merely supporting interpretation but leading the innovation. Future development of molecular spectroscopy lies to identify the niche to integrate experimental and computational molecular spectroscopy. It also requires to engineer molecular spectroscopic databases that function according to the universal approaches of computing, such as those in a Turing machine, to be realized in a chemical and/or spectroscopic programable manner (digital twinning research) in the future.

Adsorption of Fluoroquinolone Antibiotics from Water and Wastewater by Colemanite

Pharmaceutical residues in water and wastewater have become a worldwide problem with environmental and public health consequences. Antibiotics are of special importance because of the emergence of antibiotic-resistant genes. This study evaluates the adsorptive removal of four common fluoroquinolone antibiotics by using natural colemanite as an alternative adsorbent for the first time. Batch adsorption experiments were conducted for the mixture of fluoroquinolones as well as for individual compounds during the isotherm studies. Adsorption kinetic results indicated that the process followed the pseudo-second-order (PSO) model, while the Langmuir model described the sorption isotherms. The effects of pH and temperature on adsorption performance were determined, and the results indicated that the adsorption was endothermic and spontaneous, with increasing randomness at the solid-liquid interface. The effects of real water and wastewater matrices were tested by using tap water, surface water, and wastewater samples. Reusability experiments based on five adsorption-desorption cycles indicated that the adsorption performance was mostly retained after five cycles. The adsorption mechanism was elucidated based the material characterization before and after adsorption. The results indicate that colemanite can be used as an effective and reusable adsorbent for fluoroquinolone antibiotics as well as for other pollutants with similar physicochemical properties.

Solid state of inhalable high dose powders

High dose inhaled powders have received increased attention for treating lung infections. These powders can be prepared using techniques such as spray drying, spray-freeze drying, crystallization, and milling. The selected preparation technique is known to influence the solid state of the powders, which in turn can potentially modulate aerosolization and aerosolization stability. This review focuses on how and to what extent the change in solid state of high dose powders can influence aerosolization. It also discusses the commonly used solid state characterization techniques and the application of potential strategies to improve the physical and chemical stability of the amorphous powders for high dose delivery.

Quantification of clinical mAb solutions using Raman spectroscopy: Macroscopic vs microscopic analysis

Raman Spectroscopy is well emerged in the field of Analytical Quality Control (AQC) as a rapid and cost-effective technique useful in many applications. The advantage of Raman spectroscopy is the non-invasiveness of measurements that enablesto analyse samples directly in its container. In this study, the potential of Raman spectroscopy was investigated for analysis of clinical preparations of mAbs. Three commercial formulations of monoclonal antibodies (mAbs) Avastin®, Ontruzant® and Tecentriq® corresponding to Bevacizumab (BVC), Trastuzumab (TRS) and Atezolizumab (ATZ) respectively, were analysed in quartz cuvette in macroscopic analysis and through the wall of perfusion bags in microscopic analysis. The spectra have been compared to those of excipients (trehalose and sucrose) and of γ-Globulin, in order to investigate the origin of Raman bands. As expected, Raman spectra were a combination of bands from monoclonal antibodies and correspoding excipients found in formulas. For quantitative analysis of the solutions, models have been constructed using Partial Least Square Regression (PLSR) with Leave K-Out Cross Validation (LKOCV). The quantification performance was comparable for both macroscopic and microscopic analysis, in terms of error and linearity. The results are thus promising for future AQC in situ, in perfusion bags.

Monitoring the water content in NADES extracts from spirulina biomass by means of ATR-IR spectroscopy

Attenuated total reflectance-infrared spectroscopy (ATR-IR) coupled with partial least squares regression (PLSR) was evaluated as a rapid, label free and cost-effective tool to quantify water content in extracts obtained from spirulina wet biomass using a glucose glycerol natural deep eutectic solvent (NADES). NADESs are green, renewable and biodegradable solvents with unique properties outcompeting existing organic solvents, for instance, for plant or biomass extraction. The properties of NADESs depend critically on their water concentration, and therefore, it is essential to develop methods to monitor it, to ensure optimal extraction efficiency and experimental repeatability to achieve a better standardization of extraction protocols. First, Karl Fischer titration was performed on a set of 20 NADES extracts in order to obtain reference water concentrations. Secondly, ATR-IR spectra were collected and subjected to datamining to construct PLSR predictive models. An R² value of 0.9996, a mean root mean square error of cross validation of 0.136% w/w and a root mean square error of prediction of 0.130% w/w highlight the feasibility and reliability to perform quantitative analysis using ATR-IR. Moreover, the mean relative error percentage achieved, ∼0.5%, confirms the high accuracy of water concentration determination in NADES extracts. This work demonstrates that powerful alternatives are available to provide more environmentally responsible analytical protocols. ATR-IR spectroscopy applied to NADES extracts does not require any sample preparation, reagents or solvents and has minimal requirements for single use consumables. The technique is consistent with current concerns to develop greener chemistry, especially in the field of extraction of natural compounds from plants which currently represents a major focus of interest in both research and industry.

Application of UV dissolution imaging to pharmaceutical systems

UV-vis spectrometry is widely used in the pharmaceutical sciences for compound quantification, alone or in conjunction with separation techniques, due to most drug entities possessing a chromophore absorbing light in the range 190-800 nm. UV dissolution imaging, the scope of this review, generates spatially and temporally resolved absorbance maps by exploiting the UV absorbance of the analyte. This review aims to give an introduction to UV dissolution imaging and its use in the determination of intrinsic dissolution rates and drug release from whole dosage forms. Applications of UV imaging to non-oral formulations have started to emerge and are reviewed together with the possibility of utilizing UV imaging for physical chemical characterisation of drug substances. The benefits of imaging drug diffusion and transport processes are also discussed.

Hyperbolic surface wave propagation in mid-infrared metasurfaces with extreme anisotropy

Hyperbolic metasurfaces are characterized by an extreme anisotropy of their effective conductivity tensor, which may be induced at visible frequencies by sculpting metals at the subwavelength scale. In this work, we explore practical implementations of hyperbolic metasurfaces at mid-infrared wavelengths, exploiting devices composed of metals and high-index semiconductor materials, which can support the required field confinement and extreme anisotropy required to realize low loss hyperbolic surface waves. In particular, we discuss the role of broken symmetries in these hybrid metasurfaces to enable large and broadband hyperbolic responses spanning the entire mid-infrared wavelength range (3–30 μm). Our findings pave the way to the development of large scale nanophotonic devices to manipulate mid-infrared light, with applications in nonlinear optics due to the high field confinement, light routing at the nanoscale, thermal control and management, and sub diffraction imaging.

API Content and Blend Uniformity Using Quantum Cascade Laser Spectroscopy Coupled with Multivariate Analysis

The process analytical technology (PAT) initiative proposed by the US Food and Drug Administration (FDA) suggests innovative methods to better understand pharmaceutical processes. The development of analytical methods that quantify active pharmaceutical ingredients (APIs) in powders and tablets is fundamental to monitoring and controlling a drug product's quality. Analytical methods based on vibrational spectroscopy do not require sample preparation and can be implemented during in-line manufacturing to maintain quality at each stage of operations. In this study, a mid-infrared (MIR) quantum cascade laser (QCL) spectroscopy-based protocol was performed to quantify ibuprofen in formulations of powder blends and tablets. Fourteen blends were prepared with varying concentrations from 0.0% to 21.0% (w/w) API. MIR laser spectra were collected in the spectral range of 990 to 1600 cm^-1. Partial least squares (PLS) models were developed to correlate the intensities of vibrational signals with API concentrations in powder blends and tablets. PLS models were evaluated based on the following figures of merit: correlation coefficient (R²), root mean square error of calibration, root mean square error of prediction, root mean square error of cross-validation, and relative standard error of prediction. QCL assisted by multivariate analysis was demonstrated to be accurate and robust for analysis of the content and blend uniformity of pharmaceutical compounds.

In situ Analytical Quality Control of chemotherapeutic solutions in infusion bags by Raman spectroscopy

Analytical Quality Control (AQC) in centralised preparation units of oncology centers is a common procedure relying on the identification and quantification of the prepared chemotherapeutic solutions for safe intravenous administration to patients. Although the use of Raman spectroscopy for AQC has gained much interest, in most applications it remains coupled to a flow injection analyser (FIA) requiring withdrawal of the solution for analysis. In addition to current needs for more rapid and cost-effective analysis, the risk of exposure of clinical staff to the toxic molecules during daily handling is a serious concern to address. Raman spectroscopic analysis, for instance by Confocal Raman Microscopy (CRM), could enable direct analysis (non-invasive) for AQC directly in infusion bags. In this study, 3 anticancer drugs, methotrexate (MTX), 5-fluorouracil (5-FU) and gemcitabine (GEM) have been selected to highlight the potential of CRM for withdrawal free analysis. Solutions corresponding to the clinical range of each drug were prepared in 5% glucose and data was collected from infusion bags placed under the Raman microscope. Firstly, 100% discrimination has been obtained by Partial Least Squares Discriminant Analysis (PLS-DA) confirming that the identification of drugs can be performed. Secondly, using Partial Least Squares Regression (PLSR), quantitative analysis was performed with mean % error of predicted concentrations of respectively 3.31%, 5.54% and 8.60% for MTX, 5-FU and GEM. These results are in accordance with the 15% acceptance criteria used for the current clinical standard technique, FIA, and the Limits of Detection for all drugs were determined to be substantially lower than the administered range, thus highlighting the potential of confocal Raman spectroscopy for direct analysis of chemotherapeutic solutions.

The Influence of the Strength of Drug-Polymer Interactions on the Dissolution of Amorphous Solid Dispersions

In an earlier report, ionic interactions between ketoconazole (KTZ), a weakly basic drug, and poly(acrylic acid) (PAA), an anionic polymer, resulted in a dramatic decrease in molecular mobility as well as reduced crystallization propensity of amorphous solid dispersion (ASD) in the solid state. On the other hand, weaker dipole-dipole interactions between KTZ and polyvinylpyrrolidone (PVP) resulted in ASDs with higher crystallization propensity (Mistry Mol Pharm., 2015, 12 (9), 3339-3350). In this work, we investigated the behavior of the ketoconazole (KTZ) solid dispersions in aqueous media. In vitro dissolution tests showed that the PAA ASD maintained the level of supersaturation for a longer duration than the PVP ASD at low polymer contents (4-20% w/w polymer). Additionally, the PAA ASDs were more resistant to drug crystallization in aqueous medium when measured with synchrotron X-ray diffractometry. Two-dimensional ¹H nuclear Overhauser effect spectroscopy (NOESY) NMR cross peaks between ketoconazole and PAA confirmed the existence of drug-polymer interactions in D₂O. The interaction was accompanied by a reduced drug diffusivity as monitored by 2D diffusion ordered spectroscopy (DOSY) NMR and enthalpy-driven when characterized by isothermal titration calorimetry (ITC). On the other hand, drug-polymer interactions were not detected between ketoconazole and PVP in aqueous solution, with NOESY, DOSY, or ITC. The results suggest that interactions that stabilize ASDs in the solid state can also be relevant and important in sustaining supersaturation in solution.

Characterizing Drug-Polymer Interactions in Aqueous Solution with Analytical Ultracentrifugation

We present a new approach for characterizing drug-polymer interactions in aqueous media, using sedimentation velocity analytical ultracentrifugation (AUC). We investigated the potential interaction of ketoconazole (KTZ), a poorly water-soluble drug, with polyacrylic acid (PAA) and a polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus) in aqueous buffers. The effect of the polymer on the sedimentation coefficient of the drug was the observable metric. The drug alone, when subjected to AUC, exhibited a very narrow sedimentation peak at 0.2 Svedberg (S), in agreement with the expectation for a monomeric drug with a molar mass < 1000 Dalton. Conversely, the neat polymers showed broad profiles with higher sedimentation coefficients, reflecting their larger more heterogeneous size distributions. The sedimentation profiles of the drug-polymer mixtures were expectedly different from the profile of the neat drug. With KTZ-Soluplus, a complete shift to faster sedimentation times (indicative of an interaction) was observed, while with KTZ-PAA, a split peak indicated the existence of the drug in both free and interacting states. The sedimentation profile of carbamazepine, a second model drug, in the presence of hydroxypropyl methyl cellulose acetate succinate (HPMCAS, another polymer) revealed multiple "populations" of drug-polymer species, very similar to the sedimentation profile of neat HPMCAS. The interactions probed by AUC were compared with the results from isothermal titration calorimetry. In vitro dissolution tests performed on amorphous solid dispersions prepared with the same drug-polymer pairs suggested that the interactions may play a role in prolonging drug supersaturation. The results show the possibility of characterizing drug-polymer interactions in aqueous solution with high hydrodynamic resolution, addressing a major challenge frequently encountered in the mechanistic investigations of the dissolution behavior of amorphous solid dispersions.

Pharmaceutical Hydrates Analysis-Overview of Methods and Recent Advances

This review discusses a set of instrumental and computational methods that are used to characterize hydrated forms of APIs (active pharmaceutical ingredients). The focus has been put on highlighting advantages as well as on presenting some limitations of the selected analytical approaches. This has been performed in order to facilitate the choice of an appropriate method depending on the type of the structural feature that is to be analyzed, that is, degree of hydration, crystal structure and dynamics, and (de)hydration kinetics. The presented techniques include X-ray diffraction (single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD)), spectroscopic (solid state nuclear magnetic resonance spectroscopy (ssNMR), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy), thermal (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA)), gravimetric (dynamic vapour sorption (DVS)), and computational (molecular mechanics (MM), Quantum Mechanics (QM), molecular dynamics (MD)) methods. Further, the successful applications of the presented methods in the studies of hydrated APIs as well as studies on the excipients' influence on these processes have been described in many examples.

Mechanism and Improved Dissolution of Glycyrrhetinic Acid Solid Dispersion by Alkalizers

The purpose of this study was to increase the dissolution of glycyrrhetinic acid (GA) by preparing ternary solid dispersion (TSD) systems containing alkalizers, and to explore the modulating mechanism of alkalizers in solid dispersion systems. GA TSDs were prepared by hot melt extrusion (HME) with Kollidon^® VA64 as the carrier and L-arginine/meglumine as the alkalizers. The in vitro release of the TSD was investigated with a dissolution test, and the dissociation constant (pKa) was used to describe the ionization degree of the drug in different pH buffers. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and a molecular model were used for solid-state characterizations and to study the dissolution mechanism of the TSDs. It was evident that the dissolution of GA significantly increased as a result of the TSD compared to the pure drug and binary solid dispersion. SEM, DSC, and XPRD data showed that GA transformed into an amorphous form in TSD. As illustrated by FTIR, Raman, XPS, and molecular docking, high binding energy ion-pair complexes formed between GA and the alkalizers during the process of HME. These can destroy the H-bond between GA molecules. Further, intermolecular H-bonds formed between the alkalizers and Kollidon^® VA64, which can increase the wettability of the drug. Our results will significantly improve the solubility and dissolution of GA. In addition, the lower pKa value of TSD indicates that higher ionization is beneficial to the dissolution of the drug. This study should facilitate further developments of TSDs containing alkalizers to improve the dissolution of weakly acidic drugs and gain a richer understanding of the mechanism of dissolution.

Solid-State Quantification of Cocrystals in Pharmaceutical Tablets Using Transmission Low-Frequency Raman Spectroscopy

To enable the continuous production of cocrystal-containing pharmaceutical tablets, guaranteeing the cocrystal content of the final pharmaceutical tablets in the solid state is critical. This study demonstrates the quantification of caffeine-glutaric acid cocrystals in model tablets using transmission low-frequency Raman spectroscopy. Although distinguishing between cocrystals and raw materials using conventional Raman spectroscopy is difficult, the use of low-frequency Raman spectroscopy enables the discrimination of cocrystals and raw materials. Low-frequency Raman spectra were analyzed by the partial least-squares method (PLS) to obtain the predicted contents in the model tablets. To evaluate the quantitative ability of this method, the root means square error of cross-validation (RMSECV) was determined by comparing the actual concentration and predicted content with a calibration curve. For cocrystal-containing tablets, the quantitative ability of the transmission mode (RMSECV = 2.06- 3.17) was 13.4-31.4% higher than that of the backscattering mode (RMSECV= 2.37- 3.91). The coexistence of raw crystalline materials did not affect the quantitative ability for cocrystals.

Crystal Structure Optimization and Gibbs Free Energy Comparison of Five Sulfathiazole Polymorphs by the Embedded Fragment QM Method at the DFT Level

Molecular crystal plays an important role in many fields of science and technology, but it often crystallizes in different polymorphs with different physical properties. To guide the experimental synthesis of candidate materials, the atomic-scale model is frequently used to predict the most stable polymorph and its structural properties. Here, we show how an ab initio method can be used to achieve a rapid and accurate prediction of sulfathiazole crystal polymorphs (an antibiotic drug), based on the Gibbs free energy calculation and Raman spectra analysis. At the atmospheric pressure and the temperature of 300 K, we demonstrate that form III (FIII) is the most stable structure of sulfathiazole. The agreement between the predicted and experimental crystal structures corresponds to the order of stability for five sulfathiazole polymorphs as FI < FV < FIV < FII < FIII, which is achieved by employing the density functional theory (DFT) calculations.

Smart systems for determination of drug's solubility

The solubility of drugs is a crucial physicochemical property in the drug discovery or development process and for improving the bioavailability of drugs. There are various methods for evaluating the solubility of drugs including manual measurement methods, mathematical methods, and smart methods. Manual measurement and mathematical methods have some defects which make the smart systems more reliable and important in this field. In this review, various instruments used for the solubility determination, along with the smart systems, have been discussed. Mechanism and applications of each method have been elaborated in detail. Moreover, unique characteristics as well as some limitations of discussed methods are also described.

Dual mechanism of microenvironmental pH modulation and foam melt extrusion to enhance performance of HPMCAS based amorphous solid dispersion

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is an excellent polymeric carrier for melt extrusion amorphous solid dispersion. However, its pH-dependent solubility limits its application, especially for narrow absorption window drugs. The current study proposed a novel dual approach of foam extrusion and microenvironmental pH modulation to overcome this limitation. Sodium bicarbonate was used as a blowing agent and the remaining sodium carbonate acted as an internal pH modifier. Compared with conventional extrusion, foam extrusion dramatically lowered the extrudate physical strength (breaking force and hardness decreased by 20-fold; breaking energy and deformation energy decreased by >30-fold). Milling efficiency of foam extrudate was largely improved compared with that of conventional extrudates, demonstrating smaller particle size, larger specific surface area, and ability to pass through a smaller milling screen. The foam extrudate could generate a supersaturation concentration up to 8-fold higher than the solubility of the pure drug. It also significantly enhanced drug dissolution in a two-step biorelevant medium (p < 0.05). This novel approach improved both manufacturing processability and dissolution of HPMCAS-based solid dispersions.

Mid-infrared plasmonic multispectral filters

A miniaturized mid-infrared spectral analyzer will find a wide range of applications as a portable device in non-invasive disease diagnosis, environmental monitoring, food safety and others. In this work, we report an integrated spectral analyzer that can be constructed by using Au subwavelength hole arrays as multispectral filters. The hole arrays were fabricated with CMOS compatible processes. The transmission peak of the subwavelength hole arrays is continuously tuned from 3 μm to 14 μm by linearly increasing the periodicity of the holes in each array. Fourier transform infrared (FTIR) microscopy was applied to spatially map out the transmission of the hole arrays. The results show that each hole array can selectively allow for transmission at a specific wavelength. We further constructed an IR spectral analyzer model based on the microhole multispectral filters to retrieve IR spectral information of two test samples. Our experimental results show that the spectra from the integrated spectral analyzer follow nearly the same pattern of the FTIR spectra of the test samples, proving the potential of the miniaturized spectral analyzer for chemical analysis.

Recent advances in the applications of vibrational spectroscopic imaging and mapping to pharmaceutical formulations

Vibrational spectroscopic imaging and mapping approaches have continued in their development and applications for the analysis of pharmaceutical formulations. Obtaining spatially resolved chemical information about the distribution of different components within pharmaceutical formulations is integral for improving the understanding and quality of final drug products. This review aims to summarise some key advances of these technologies over recent years, primarily since 2010. An overview of FTIR, NIR, terahertz spectroscopic imaging and Raman mapping will be presented to give a perspective of the current state-of-the-art of these techniques for studying pharmaceutical samples. This will include their application to reveal spatial information of components that reveals molecular insight of polymorphic or structural changes, behaviour of formulations during dissolution experiments, uniformity of materials and detection of counterfeit products. Furthermore, new advancements will be presented that demonstrate the continuing novel applications of spectroscopic imaging and mapping, namely in FTIR spectroscopy, for studies of microfluidic devices. Whilst much of the recently developed work has been reported by academic groups, examples of the potential impacts of utilising these imaging and mapping technologies to support industrial applications have also been reviewed.

A comparative study between hot-melt extrusion and spray-drying for the manufacture of anti-hypertension compatible monolithic fixed-dose combination products

The purpose of this work was to investigate the application of different advanced continuous processing techniques (hot melt extrusion and spray drying) to the production of fixed-dose combination (FDC) monolithic systems comprising of hydrochlorothiazide and ramipril for the treatment of hypertension. Identical FDC formulations were manufactured by the two different methods and were characterised using powder X-ray diffraction (PXRD) and modulated differential scanning calorimetry (mDSC). Drug dissolution rates were investigated using a Wood's apparatus, while physical stability was assessed on storage under controlled temperature and humidity conditions. Interestingly both drugs were transformed into their amorphous forms when spray dried, however, hydrochlorothiazide was determined, by PXRD, to be partially crystalline when hot melt extruded with either polymer carrier (Kollidon® VA 64 or Soluplus®). Hot melt extrusion was found to result in significant degradation of ramipril, however, this could be mitigated by the inclusion of the plasticizer, polyethylene glycol 3350, in the formulation and appropriate adjustment of processing temperature. The results of intrinsic dissolution rate studies showed that hot-melt extruded samples were found to release both drugs faster than identical formulations produced via spray drying. However, the differences were attributable to the surface roughness of the compressed discs in the Wood's apparatus, rather than solid state differences between samples. After a 60-day stability study spray dried samples exhibited a greater physical stability than the equivalent hot melt extruded samples.

Mid-infrared upconversion based hyperspectral imaging

Mid-infrared hyperspectral imaging has in the past decade emerged as a promising tool for medical diagnostics. In this work, nonlinear frequency upconversion based hyperspectral imaging in the 6 to 8 µm spectral range is presented for the first time, using both broadband globar and narrowband quantum cascade laser illumination. AgGaS₂ is used as the nonlinear medium for sum frequency generation using a 1064 nm mixing laser. Angular scanning of the nonlinear crystal provides broad spectral coverage at every spatial position in the image. This study demonstrates the retrieval of series of monochromatic images acquired by a silicon based CCD camera, using both broadband and narrowband illumination and a comparison is made between the two illumination sources for hyperspectral imaging.

Recent progress of structural study of polymorphic pharmaceutical drugs

This review considers advances in the understanding of active pharmaceutical ingredient polymorphism since around 2010 mainly from a structural view point, with a focus on twelve model drugs. New polymorphs of most of these drugs have been identified despite that the polymorphism of these old drugs has been extensively studied so far. In addition to the conventional modifications of preparative solvents, temperatures, and pressure, more strategic structure-based methods have successfully yielded new polymorphs. The development of analytical techniques, including X-ray analyses, spectroscopy, and microscopy has facilitated the identification of unknown crystal structures and also the discovery of new polymorphs. Computational simulations have played an important role in explaining and predicting the stability order of polymorphs. Furthermore, these make significant contributions to the design of new polymorphs by considering structure and energy. The new technologies and insights discussed in this review will contribute to the control of polymorphic forms, both during manufacture and in the drug formulation.

Pharmaceutical cocrystals, salts and polymorphs: Advanced characterization techniques

The main goal of a novel drug development is to obtain it with optimal physiochemical, pharmaceutical and biological properties. Pharmaceutical companies and scientists modify active pharmaceutical ingredients (APIs), which often are cocrystals, salts or carefully selected polymorphs, to improve the properties of a parent drug. To find the best form of a drug, various advanced characterization methods should be used. In this review, we have described such analytical methods, dedicated to solid drug forms. Thus, diffraction, spectroscopic, thermal and also pharmaceutical characterization methods are discussed. They all are necessary to study a solid API in its intrinsic complexity from bulk down to the molecular level, gain information on its structure, properties, purity and possible transformations, and make the characterization efficient, comprehensive and complete. Furthermore, these methods can be used to monitor and investigate physical processes, involved in the drug development, in situ and in real time. The main aim of this paper is to gather information on the current advancements in the analytical methods and highlight their pharmaceutical relevance.

Water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) amorphous solid dispersions: Insights with confocal fluorescence microscopy

The aim of this study was to evaluate the utility of confocal fluorescence microscopy (CFM) to study the water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) (mico-PVPVA) amorphous solid dispersions (ASDs), induced during preparation, upon storage at high relative humidity (RH) and during dissolution. Different fluorescent dyes were added to drug-polymer films and the location of the dyes was evaluated using CFM. Orthogonal techniques, in particular atomic force microscopy (AFM) coupled with nanoscale infrared spectroscopy (AFM-nanoIR), were used to provide additional analysis of the drug-polymer blends. The initial miscibility of mico-PVPVA ASDs prepared under low humidity conditions was confirmed by AFM-nanoIR. CFM enabled rapid identification of drug-rich and polymer-rich phases in phase separated films prepared under high humidity conditions. The identity of drug- and polymer-rich domains was confirmed using AFM-nanoIR imaging and localized IR spectroscopy, together with Lorentz contact resonance (LCR) measurements. The CFM technique was then utilized successfully to further investigate phase separation in mico-PVPVA films exposed to high RH storage and to visualize phase separation dynamics following film immersion in buffer. CFM is thus a promising new approach to study the phase behavior of ASDs, utilizing drug and polymer specific dyes to visualize the evolution of heterogeneity in films exposed to water.

Chemometrics-assisted solid-state characterization of pharmaceutically relevant materials. Polymorphic substances

Current regulations command to properly characterize pharmaceutically relevant solid systems. Chemometrics comprise a range of valuable tools, suitable to process large amounts of data and extract valuable information hidden in their structure. This review aims to detail the results of the fruitful association between analytical techniques and chemometrics methods, focusing on those which help to gain insight into the characteristics of drug polymorphism as an important aspect of the solid state of bulk drugs and drug products. Hence, the combination of Raman, terahertz, mid- and near- infrared spectroscopies, as well as instrumental signals resulting from X-ray powder diffraction, ¹³C solid state nuclear magnetic resonance spectroscopy and thermal methods with quali-and quantitative chemometrics methodologies are examined. The main issues reviewed, concerning pharmaceutical drug polymorphism, include the use of chemometrics-based approaches to perform polymorph classification and assignment of polymorphic identity, as well as the determination of given polymorphs in simple mixtures and complex systems. Aspects such as the solvation/desolvation of solids, phase transformation, crystallinity and the recrystallization from the amorphous state are also discussed. A brief perspective of the field for the next future is provided, based on the developments of the last decade and the current state of the art of analytical instrumentation and chemometrics methodologies.

Methods to characterize the structure of food powders – a review

Food powders can exist in amorphous, crystalline or mixed structure depending on the order of molecular arrangement in the powder particle matrices. In food production, the structure of powders has a greatly effect on their stability, functionality, and applicability. The undesirable structure of powders can be accidentally formed during production. Therefore, characterization of powder structure as well as quantification of amorphous–crystalline proportions presenting in the powders are essential to control the quality of products during storage and further processing. For these purposes, many analytical techniques with large differences in the degree of selectivity and sensitivity have been developed. In this review, differences in the structure of food powders are described with a focus being placed on applications of amorphous powders. Essentially, applicability of common analytical techniques including X-ray, microscopic, vapor adsorption, thermal, and spectroscopic approaches for quantitative and qualitative structural characterization of food powders is also discussed.

Quantification of Multiple Components of Complex Aluminum-Based Adjuvant Mixtures by Using Fourier Transform Infrared Spectroscopy and Partial Least Squares Modeling

Fourier transform infrared (FTIR) spectroscopy is widely used in the pharmaceutical industry for process monitoring, compositional quantification, and characterization of critical quality attributes in complex mixtures. Advantages over other spectroscopic measurements include ease of sample preparation, quantification of multiple components from a single measurement, and the ability to quantify optically opaque samples. This method describes the use of a multivariate model for quantifying a TLR4 agonist (GLA) adsorbed onto aluminum oxyhydroxide (Alhydrogel^®) using FTIR spectroscopy that may be adapted to quantify other complex aluminum based adjuvant mixtures.

Using mid infrared technology as new method for the determination of the dwell time of salivary substitutes on three dimensional gingiva models

Background

Many people suffer from dry mouth (xerostomia) due to radiotherapy treatment of head and neck cancer, diseases like Sjogren’s syndrome or as adverse effects to prescribed medications. Salivary substitute products like gels or sprays are often used for treatment. Efficacy of those oral care products are regularly assessed by validated or even not validated questionnaires. To determine the adhesion effect over time more objectively a new and sensitive method was established. The following study was designed to assess the dwell time of different oral care products in vitro.

Method

Two different types of surfaces were covered with oral care products and washed using a definite protocol with artificial saliva salt solution. First, oral care gels or oral care sprays were spread to a polystyrene surface of 2.25 cm², then onto cell based three-dimensional gingiva models. The surfaces were washed ten times with artificial saliva salt solution. The resulting washing solutions were examined using mid infrared spectroscopy in order to detect ingredients of the oral care products.

Results

All assessed oral care gels or oral care sprays and their components were detected very sensitive. Even traces of the products were detected in the eluent and thus enabled to differentiate the dwell times of the different products. In general, the dwell time of oral care gels on polystyrene or gingiva models was longer than that of oral care sprays. The use of gingiva models improved the differentiation between different products.

Conclusions

MIR spectroscopy turned out to be a sensitive method to detect salivary substitutes. Differences between single components and different products can be detected. The described method is a simple, reliable and easy process to evaluate the dwell time of oral care products in vitro and thus a useful tool to design optimised salivary substitute products.

Ethics

This is an in vitro study. No ethics or consent was required for this study.

Miscibility of Itraconazole-Hydroxypropyl Methylcellulose Blends: Insights with High Resolution Analytical Methodologies

Drug-polymer miscibility is considered to be a prerequisite to achieve an optimally performing amorphous solid dispersion (ASD). Unfortunately, it can be challenging to evaluate drug-polymer miscibility experimentally. The aim of this study was to investigate the miscibility of ASDs of itraconazole (ITZ) and hydroxypropyl methylcellulose (HPMC) using a variety of analytical approaches. The phase behavior of ITZ-HPMC films prepared by solvent evaporation was studied before and after heating. Conventional methodology for miscibility determination, that is, differential scanning calorimetry (DSC), was used in conjunction with emerging analytical techniques, such as fluorescence spectroscopy, fluorescence imaging, and atomic force microscopy coupled with nanoscale infrared spectroscopy and nanothermal analysis (AFM-nanoIR-nanoTA). DSC results showed a single glass transition event for systems with 10% to 50% drug loading, suggesting that the ASDs were miscible, whereas phase separation was observed for all of the films based on the other techniques. The AFM-coupled techniques indicated that the phase separation occurred at the submicron scale. When the films were heated, it was observed that the ASD components underwent mixing. The results provide new insights into the phase behavior of itraconazole-HPMC dispersions and suggest that the emerging analytical techniques discussed herein are promising for the characterization of miscibility and microstructure in drug-polymer systems. The observed differences in the phase behavior in films prepared by solvent evaporation before and after heating also have implications for processing routes and suggest that spray drying/solvent evaporation and hot melt extrusion/melt mixing can result in ASDs with varying extent of miscibility between the drug and the polymer.

A fourier transform infrared spectroscopy (FTIR) based assay for Candida parapsilosis ATCC 7330 mediated oxidation of aryl alcohols

We present an FTIR based assay to monitor the whole cell mediated oxidation of aryl alcohols by measuring the characteristic IR absorption of the hydroxyl group [OH] of the substrate and the carbonyl group [CO] of the corresponding oxidized product. This method expedites the analysis of whole cell mediated catalysis which is usually done by GC and/or HPLC. The FTIR assay had linearity with R(2)≥0.980 and sensitivity up to 10μM. The accuracy and precision of FTIR assay was found ≥81% and ≥94%, respectively. This assay was validated by GC which exhibited ≥82% accuracy and ≥79% precision. The time of analysis taken by this assay was 2-3min per sample in comparison with 20-40min by GC.

Development of a univariate membrane-based mid-infrared method for protein quantitation and total lipid content analysis of biological samples

Biological samples present a range of complexities from homogeneous purified protein to multicomponent mixtures. Accurate qualification of such samples is paramount to downstream applications. We describe the development of an MIR spectroscopy-based analytical method offering simultaneous protein quantitation (0.25-5 mg/mL) and analysis of total lipid or detergent species, as well as the identification of other biomolecules present in biological samples. The method utilizes a hydrophilic PTFE membrane engineered for presentation of aqueous samples in a dried format compatible with fast infrared analysis. Unlike classical quantification techniques, the reported method is amino acid sequence independent and thus applicable to complex samples of unknown composition. By comparison to existing platforms, this MIR-based method enables direct quantification using minimal sample volume (2 µL); it is well-suited where repeat access and limited sample size are critical parameters. Further, accurate results can be derived without specialized training or knowledge of IR spectroscopy. Overall, the simplified application and analysis system provides a more cost-effective alternative to high-throughput IR systems for research laboratories with minimal throughput demands. In summary, the MIR-based system provides a viable alternative to current protein quantitation methods; it also uniquely offers simultaneous qualification of other components, notably lipids and detergents.

Quantitative measurement of Toll-like receptor 4 agonists adsorbed to Alhydrogel(®) by Fourier transform infrared-attenuated total reflectance spectroscopy

Aluminum salts have a long history as safe and effective vaccine adjuvants. In addition, aluminum salts have high adsorptive capacities for vaccine antigens and adjuvant molecules, for example, Toll-like receptor 4 (TLR4) agonists. However, the physicochemical properties of aluminum salts make direct quantitation of adsorbed molecules challenging. Typical methods for quantifying adsorbed molecules require advanced instrumentation, extreme sample processing, often destroy the sample, or rely on an indirect measurement. A simple, direct, and quantitative method for analysis of adsorbed adjuvant molecules is needed. This report presents a method utilizing Fourier transform infrared spectroscopy with a ZnSe-attenuated total reflectance attachment to directly measure low levels (<30 μg/mL) of TLR4 agonists adsorbed on aluminum salts with minimal sample preparation.

The local environment of Dy3+in selenium-rich chalcogenide glasses

The environment of Dy³⁺is investigated when it is added as DyCl₃or Dy foil into two base glasses, Ge_16.5As_19−xGa_xSe_64.5, wherex= 3 or 10 at%, at doping levels between 0 and 3000 parts per million by weight (ppmw) Dy³⁺.

Atomic force microscope infrared spectroscopy of griseofulvin nanocrystals

The goal of this work was to evaluate the ability of photothermal-induced resonance (PTIR) to measure the local infrared absorption spectra of crystalline organic drug nanoparticles embedded within solid matrices. Herein, the first reports of the chemical characterization of sub-100 nm organic crystals are described; infrared spectra of 90 nm griseofulvin particles were obtained, confirming the chemical resolution of PTIR beyond the diffraction limit. Additionally, particle size distributions via dynamic light scattering and PTIR image analysis were found to be similar, suggesting that the PTIR measurements are not significantly affected by inhomogeneous infrared absorptivity of this system. Thus as medical applications increasingly emphasize localized drug delivery via micro/nanoengineered structures, PTIR can be used to unambiguously chemically characterize drug formulations at these length scales.

Evaluation of analytical tools and multivariate methods for quantification of co-former crystals in ibuprofen-nicotinamide co-crystals

Co-crystals are multicomponent substances designed by the addition of two or more different molecules in a same crystallographic pattern, in which it differs from the crystallographic motif of its co-formers. The addition of highly soluble molecules, like nicotinamide, in the crystallographic pattern of ibuprofen enhances its solubility more than 7.5 times, improving the properties of this widely used drug. Several analytical solid state techniques are used to characterize the ibuprofen-nicotinamide co-crystal, being the most used: mid-infrared (ATR-FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRPD) and Raman spectroscopy. These analytical solid state techniques were evaluated to quantify a mixture of ibuprofen-nicotinamide co-crystal and its co-formers in order to develop a calibration model to evaluate the co-crystal purity after its synthesis. Raman spectroscopy showed better result than all other techniques with a combination of multivariate calibration tools, presenting lower values of calibration and prediction errors. The partial least squares regression model gave a mean error lower than 5% for all components presented in the mixture. DSC and mid-infrared spectroscopy proved to be insufficient for quantification of the ternary mixture. XRPD presented good results for quantification of the co-formers, ibuprofen and nicotinamide, but fair results for the co-crystal. This is the first report of quantification of ibuprofen-nicotinamide co-crystal, among its co-formers. The quantification is of great importance to determine the yield of the co-crystallization reactions and the purity of the product obtained.