thermal analysis cma 220412 presentation - tcd.ie · thermal analysis techniques iupac definition...
TRANSCRIPT
Thermal Analysis
Dr. Lidia Tajber
School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin
Characterisation for Pharma
� Active pharmaceutical ingredients (API, drugs)� Organic molecules, peptides, proteins
� Single components
� Mainly solids (crystalline, amorphous or semi-crystalline)
� Pure molecules
� Excipients (additives, fillers etc.)� Organic, inorganic
� Not always single components
� Solids or liquids
� Not always pure
� Formulations (dosage forms, delivery systems)� Mixtures of APIs and excipients
� Packaging materials
Physical Forms of Solids
� Polymorphism - the ability of a
compound to crystallise in more
than one crystal form
� Pseudopolymorphic forms
(solvated forms) - crystalline solids
containing solvent molecules as an
integral part of their crystal
structure
� Amorphism - the absence of
regular or crystalline structure in a
body solid; amorphous materials
do not possess three-dimensional
long-range molecular order
Polymorph A Polymorph B
Solvate A Solvate B
Different thermal behaviour
Importance of Solid State Forms in Pharma
� Bioavailability (solubility/dissolution rate)
� Stability (physical and chemical)
� Processing factors
� Hygroscopicity
� Bulk and mechanical properties
� Ease of isolation, filtration and drying
� Degree of purity
Thermal Analysis Techniques
� IUPAC definition - a group of techniques in which a
physical property is measured as a function of
temperature, while the sample is subjected to a
controlled temperature programme (heating, cooling or
isothermal).
� A range of techniques e.g.:
� Differential Thermal Analysis (DTA) – temperature
� Differential Scanning Calorimetry (DSC) – energy
� Thermogravimetric Analysis (TGA) – mass
� Thermomechanical Analysis (TMA) – dimensions
Basic Principles of Thermal Analysis
� Modern instrumentation used for thermal analysis
usually consists of the following parts:
� sample holder/compartment for the sample
� sensors to detect/measure a property of the sample and the
temperature
� an enclosure within which the experimental parameters
(temperature, speed, environment) may be controlled
� a computer to control data collection and processing
sample
sensors
temperature
control (furnace)PC
Differential Scanning Calorimetry (DSC)
� Most popular thermal technique
� DSC measures the heat absorbed or liberated during the various transitions in the sample due to temperature treatment� Differential: sample relative to reference
� Scanning: temperature is ramped
� Calorimeter: measures heat
� DSC measurements are both qualitative and quantitative and provide information about physical and chemical changes involving:� Endothermic processes – sample absorbs energy
� Exothermic processes – sample releases energy
� Changes in heat capacity
Principles of DSC Analysis� Power Compensation DSC
� High resolution / high sensitivity research studies
� Absolute specific heat measurement
� Very sensitive to contamination of sample holders
� Heat Flux DSC
� Routine applications
� Near / at line testing in harsh environments
� Automated operation
� Cost-sensitive laboratories
Summary of Pharmaceutically Relevant Information
Derived from DSC Analysis
� Melting points – crystalline materials
� Desolvation – adsorbed and bound solvents
� Glass transitions – amorphous materials
� Heats of transitions – melting, crystallisation
� Purity determination – contamination, crystalline/amorphous phase quantification
� Polymorphic transitions – polymorphs and pseudopolymorphs
� Processing conditions – environmental factors
� Compatibility – interactions between components
� Decomposition kinetics – chemical and thermal stability
Typical Features of a DSC Trace
40 60 80 100 120 140 160 180 200 220 240 260 280 300
20
m W
tem pera tu re [oC ]
^exo Exothermic upwards
Endothermic downwards
Y-axis – heat flow
X-axis – temperature (and time)
DESOLVATIONGLASS TRANSITIONCRYSTALLISATION
MELTING
DECOMPOSITION
H2O
Melting Point
40 60 80 100 120 140 160 180 200 220 240 260 280 300
20
mW
^exo
tem perature [oC]
DSC scan of a crystalline material – one polymorphic form
MELTING
Onset = melting point (mp)
Heat of fusion (melting) = integration of peak
Polymorphic Forms
40 60 80 100 120 140 160 180 200 220 240 260 280 300
20
mW
tem perature [oC]
^exo
DSC scan of a crystalline material – polymorphic transition
METASTABLE
FORM
TRANSITION
STABLE
FORM
Pseudopolymorphism
40 60 80 100 120 140 160 180 200 220 240 260 280 300
20
mW
^exo
temperature [oC]
DSC scan of a hydrate
MELTING
DEHYDRATION
Amorphous Material
40 60 80 100 120 140 160 180 200 220 240 260 280 300
tem perature [°C ]
1 m W
DEHYDRATION
GLASS TRANSITION
Midpoint = glass transition (Tg)
Polyvinylpyrrolidone (PVP) co-processed with hydroflumethiazide
Purity Determination
Purity of phenacetin Source: TA Instruments, Cassel RB, Purity Determination and DSC Tzero™ Technology
Variants of DSC
� Conventional – linear temperature (cooling, heating) programme
� Fast scan DSC – very fast scan rates (also linear)
� MTDSC (modulated temperature DSC) – more complex temperature programmes, particularly useful in the investigation of glass transitions (amorphous materials)
� HPDSC (high pressure DSC) – stability of materials, oxidation processes
Fast Scan DSC, Rapid Scanning DSC, (HyperDSCTM)
� This method provides the ability to perform valid heat flow measurements while heating or cooling a sample with fast linear controlled rates � HyperDSCTM - rates up to 500°C/min
� Other non-commercial systems - up to 100,000°C/min
� Benefits:� Increased sensitivity for detection of weak transitions
� Analysis of samples without inducing changes
� Small sampling requirements – a fraction of mg can be used
� Fast screening for high throughput requirements - a quick overview of new samples
� Disadvantages:� Accuracy: transitions can be shifted by as much as 40oC
� Repeatabiliy: very sensitive to thermal lag and sample preparation
Fast Scan DSC, Rapid Scanning DSC, (HyperDSCTM)
� Pharma applications:
� Enhanced analysis of polymorphism
� Detection of low level amorphous content
� Suppression of decomposition – “true” melting points
� Detection of low energy transitions
� Characterisation close to processing conditions
� Separation of overlapping events
Modulated Temperature DSC (MTDSC)
� This technique uses composite heating profile: determines heat capacity and separates heat flow into the reversible and non-reversible components
� Benefits� Increased sensitivity for detecting weak transitions –
especially glass transition
� Separation of complex events into their:� heat capacity (reversible) e.g. glass transition, melting and
� kinetic components (non-reversible) e.g. evaporation, crystallisation, decomposition
� Disadvantages� Slow data collection
� Risk of sample transformation
Variants of MTDSC
� Sinusoidal modulation (easy, only one frequency only) – TA Instruments
� Step scan modulation (easy, precise) –PerkinElmer
� TOPEM® modulation (stochastic modulation, complex calculations, but multiple frequency data) – Mettler Toledo
Example of a MTDSC Curve
Polyethylene terephthalate (PET)Source: Craig DQM and Reading MThermal analysis of pharmaceuticals
Thermogravimetric Analysis (TGA)
� A technique measuring the variation in mass of a sample undergoing temperature scanning in a controlled atmosphere
� Thermobalance allows for monitoring sample weight as a function of temperature
� The sample hangs from the balance inside the furnace and the balance is thermally isolated from the furnace
balance
sample
furnacepurge gas
Summary of Pharmaceutically Relevant Information
Derived from TGA Analysis
� Desolvation – adsorbed and bound solvents,
stoichiometry of hydrates and solvates
� Decomposition – chemical and thermal stability
� Compatibility – interactions between components
Examples of TGA Curves
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320
2
mg
temperature [oC]
TGA curves of crystalline and amorphous substance
Lactose monohydrate
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 3400
^exo
20
mW
temperature [oC]
2
mg
DSC and TGA scans of lactose monohydrate
Hyphenated Thermal Equipment
� Thermal techniques alone are insufficient to prove the existence of polymorphs and solvates
� Other complementary techniques are used e.g. microscopy, diffraction and spectroscopy
� Simultaneous analysis� Types:
� DSC-TGA � DSC-XRD – DSC coupled with X-ray diffraction� TGA-MS – TG system coupled with a mass spectrometer � TGA-FTIR – TG system coupled with a Fourier Transform
infrared spectrometer � TGA -MS or -FTIR - evolved gas analysis (EGA)
� others