Pharmaceutical Raw Materials Characterization

Characterization of Pharmaceutical Raw Materials

• Lecture given by Prof. A. A. Attama, FAS on 23.10.2023.
• Students will be able to describe and understand different characterization methods for raw and starting materials.
• The methods will be either thermal (DSC, TGA etc) or non-thermal (NIR, FTIR etc).
• Students will learn the applications and advantages of the different characterization methods.

Thermal and Non-Thermal Analyses

• Analyzing pharmaceutical compounds, complex modern formulations, regulatory submissions depends on a range of analysis technologies. UV analysis, X-ray and NMR spectroscopy are some examples.

Pharmaceutical Analysis

• Analytical techniques assess bulk drug materials, intermediates, drug products, formulations, impurities, degradation products, and biological samples containing drugs/metabolites during drug development.
• The aim is to understand the physical/chemical stability, impact on dosage form, stability of drug molecules, and quantity/identity of impurities, to confirm the safety of the medicine during development..

Thermal Analysis

• Physical properties of a substance are measured as a function of temperature under a controlled temperature program.
• Active pharmaceutical ingredients(API) are tested for polymorphism, melting point, glass transition of amorphous fractions, content determination, effect of moisture, existence of solvates, and purity analysis.
• Formulations are tested for compatibility of excipients, shelf life, thermal degradation, and moisture determination.
• Packaging materials are tested for primary and secondary packaging materials, thermal stability, moisture determination, coatings, blister package interactions, and effect of repackaging.

Thermal Analysis Techniques

• Differential Scanning Calorimetry (DSC)
• Thermogravimetric Analysis (TGA)
• Dynamic Mechanical Analysis (DMA)
• Polarized Light Microscopy (PLM)-Hot stage
• Isothermal Heat Conduction Microcalorimetry (IHCM)

Thermo-Optical Analysis (TOA)

• DSC + Microscopy, and PLM-Hot stage.

Thermomechanical Analysis (TMA)

• Dimensional changes of a sample are measured as it is heated or cooled in a defined atmosphere.

Dynamic Mechanical Analysis (DMA)

• Mechanical properties of viscoelastic materials are measured as a function of time, temperature, and frequency when deformed under periodic stress.

Thermo-Optical Techniques

• DSC Microscopy and Hot-stage microscopy

Analytical Applications of Thermo-Optical Analysis (TOA)

• Identify solid-solid transitions
• Separation of overlapping effects
• Identification of the cause of an artifact
• Study of morphological behavior

Polarized Light Microscopy (PLM)

• Regular light microscopes use unpolarized white light, where waves vibrate in random directions
• Polarized light has waves vibrating in only one direction.
• Polarizing microscopes observe birefringent properties of anisotropic specimens: image contrast or color changes are observed.
• PLM is an analytical technique used in fats to observe the microstructures of the various polymorphic forms.
• It observes microstructural changes in fats during melting, as the lipid passes from crystalline to isotropic phase.
• Cross polarized lights are used with two polarizers with perpendicular orientation on incident and reflected lights.
• Birefringent structures are visible under cross-polarized light.
• Processes: dynamic crystallization and static crystallization

Dynamic Mechanical Analysis (DMA)

• Viscoelastic behavior of a material is measured across a wide frequency range.
• The technique is also used to provide information on mechanical moduli, compliances and damping behavior.

Analytical Applications of DMA

• Glass transition of amorphous components
• Viscoelastic behavior and elastic modulus
• Softening temperature
• Effect of moisture on the modulus
• Dynamic mechanical behavior of polymer packaging materials, coating materials, and formulations

Differential Scanning Calorimetry (DSC)

• The difference in energy inputs is measured as a function of temperature.
• A substance or reaction product and reference material are subjected to a controlled temperature program.
• DSC is the most widely used thermal analysis method.

DSC

• Determines the energy absorbed or released by a sample when heated or cooled.
• It studies thermal behavior and events like melting, solid-solid transitions, and chemical reactions.
• DSC is a highly sensitive technique to study the thermotropic properties of materials.

Principle of DSC

• In phase transition heat flow to a sample maintains temperature is measured relative to a reference.
• Depends on whether the process is exothermic or endothermic.
• Sample melting to a liquid the sample will require more heat flow. Sample absorbs heat during the endothermic phase transition from solid to liquid.

Types of DSC instrument

• Heat flux DSC
• Power compensated DSC
• Others include: Modulated DSC, Hyper DSC, and Pressure DSC

DSC Output

• A DSC measurement's thermogram plots the difference in heat delivered to the sample versus the reference as a function of temperature.
• The enthalpy change (ΔH) of transition is related to the area under the thermogram curve.

DSC Transitions

• Phase transitions are of two types: first and second order transitions.
• Vaporization, melting, or crystallization are first order transitions.
• The glass transition (Tg)) is a second order transition.
• First and second order transitions are distinguished from the shape of the signal on a DSC thermogram.
• Latent heat is evolved during a first order transformation.
• Second order transitions do not have accompanying latent heats.

Analytical Applications of DSC

• Melting and crystallization behavior
• Polymorphism
• Glass transition
• Enthalpy of transition
• Heat capacity
• Evaporation
• Effect of impurities on melting behavior
• Chemical reactions

A Typical DSC Curve of a Crystalline Substance includes

• Initial deflection proportional to the heat capacity of the sample
• Evaporation of moisture
• Part of the DSC curve with no thermal effects, i.e. baseline
• Melting peak
• Onset of oxidation in air

Glass Transition Temperature (Tg)

• Glass Transition is related to the presence of amorphous structures in a sample.
• Glass Transition is detected by DSC with a step-change in molecular mobility resulting in a step increase in heat capacity (ΔCp) and heat flow rate.
• Amorphous materials flow, they do not melt and so there is no DSC melt peak.
• Glass transition is not a first order transition, it is observed the the amorphous region of a polymer.
• Long polymer chains are oriented randomly in this region.

Glass Transition Size (ΔCp)

• The ΔCp at Tg measures the flexibility.
• A larger value implies a more rubbery material, e.g., polybutadiene.
• Stiffer polymers like polystyrene are have a lower value.

Thermogravimetric Analysis (TGA)

• The mass of a sample is measured as it is heated or cooled in a defined atmosphere.

TGA

• Most TGA curves display weight losses due to chemical reactions or physical transitions.
• Chemical reactions cause decomposition and loss of water of crystallization, combustion, reduction of metal oxides
• Physical transitions cause vaporization, evaporation, sublimation, desorption, and drying.
• Occasionally weight gain is observed due to chemical reactions, and physical transitions.
• Chemical reactions involve reaction with gaseous substances in the purge gas such as O2, CO2 with formation of nonvolatile or hardly volatile compounds.
• Physical transitions involve adsorption of gaseous substances on samples such as active charcoal.

A typical TGA curve of a pharmaceutical preparation includes

• Volatiles such as moisture and solvents
• Loss of water of crystallization
• Decomposition
• Residue (ash, inorganic fillers)
• It is used to investigate processes such as the loss of volatile substances or decomposition.
• Evolved gases can be analyzed online using hyphenated techniques such as TGA-MS or TGA-FTIR.

Analytical Applications of TGA

• Compositional analysis
• Evaporation, desorption, and vaporization
• Thermal stability and decomposition
• Kinetics of reactions
• Reaction stoichiometry

Differential Thermal Analysis (DTA)

• The difference in temperature is measured between the sample and a reference material, monitored against time or temperature.
• The temperature of the sample, in a specified atmosphere, is programmed.
• DTA is mostly used for qualitative measurement and that it is more robust because less sensitive material is used for sample holder.
• It also informs about glass transitions, melting points, sample purity, and crystallization.

Non-Thermal Techniques

• Spectroscopy
• X-ray
• Chromatography (TLC, HPTLC, HPLC, GC-MS)

Near-Infrared Spectroscopy (NIR)

• A rapid alternative to time-consuming, solvent intensive, wet-chemistry and chromatographic methods.
• NIR helps to quickly verify raw materials and monitor reaction progress, allowing quantification of final products.
• NIR advantages: no sample preparation, non-destructive measurement, accuracy, reliability, reduced cost, and increased throughput.
• NIR provides solutions from drug development to QA/QC lab, and in at-line, on-line, or continuous manufacturing processes.

Fourier Transform Infrared (FTIR)

• It obtains an infra-red spectrum of absorption/emission of a solid, liquid, or gas.
• Spectra reveal the composition of solids, liquids, and gases.
• It is used in the identification of unknown materials and confirmation of of production materials (incoming or outgoing).
• Information is content is very specific, permitting fine discrimination between like materials.
• The speed of analysis makes it particularly useful in screening applications.

FTIR Spectrometers can preform

• Raw material identification
• Detect incompatibility
• Differentiate between polymorphs
• Analyze formulated products with specificity, speed, and reliability
• Microanalysis of small sections of materials to identify contaminants
• Analysis of thin films and coatings

Raman Spectroscopy

• Raman spectra detect structural changes and molecular bonding in materials.
• The technique uses photons from a laser source, typically from infrared to UV wavelengths.
• A few of the incident photons undergo Raman scattering, losing energy through exciting vibrational modes of the sample.
• It can be used in any application where non-destructive, microscopic, chemical analysis and imaging is required.

Raman Spect. Applications

• Compound distribution in tablets
• Blend uniformity
• High throughput screening
• API concentration
• Powder content and purity
• Raw material verification
• Polymorphic forms
• Crystallinity
• Contaminant identification
• Combinational chemistry
• In vivo analysis and skin depth profiling
• Dosage, content uniformity.

X-Ray Analysis

• X-ray diffraction (XRD)
• X-ray scattering (XRS)
• X-ray fluorescence (XRF)
• These are valuable and non-destructive techniques for drug discovery, development and manufacture

X-Ray Diffraction (XRD)

• The X-rays reflecting off different planes must interfere constructively to form an interference pattern; otherwise they interfere destructively with no pattern.
• X-Ray Diffraction results from constructive interference betweek X-rays and a crystalline sample.
• XRD: crystal structures can be determined, polymorphs or hydrates screened for, changes in morphology or state of active ingredients detected, crystalline impurities detected/quantified, the size of crystallites/crystallinity is determined, and the final forms optimized.
• XRPD data is required for new product registration and patent application/protection.
• Wide angle X-ray diffraction (WAXD) used for the analysis of the short range order of crystalline material.
• Small angle X-ray diffraction (SAXD) performs analysis of the long range order of crystalline materials.
• Small-angle x-ray diffraction (SAXD): 0.1-10°, Wide-angle x-ray diffraction (WAXD): >10°

X-Ray Scattering Techniques

• When x-rays illuminate a sample they deflect and scatter, creating complex patterns.
• The patterns', intensities, scatter angles, changes in polarization, wavelength, and/or energy can reveal structural, elemental, and atomic information.
• SAXS (0.1-10°) produces nanoscale resolution (samples 100-1 nm), while WAXS (>10°) has atomic resolution (1-0.1 nm).
• SAXS analyzes larger scale bulk microstructure while WAXS is like x-ray diffraction and observes atomic details.

X-Ray Fluorescence (XRF)

• XRF spectroscopy is a non-destructive technique, requiring little/no sample preparation.
• It detects/quantifies major and minor elements in fillers, lubricants, coatings, and other excipients (sub-ppm levels).
• It precisley quantifies catalyst residues present in APIs or final drug products.