API Thermal Properties: Thermal Events and Stability by DSC and TGA
API thermal properties by DSC and TGA is the characterization of thermal events — melting, recrystallization and glass transition — and of mass loss, volatiles content and thermal stability of a formulation's components. The study supports API-excipient compatibility screening, safe process-window definition, and investigation of hydrates, solvates and amorphous content.
What is thermal properties characterization by DSC and TGA?
DSC (differential scanning calorimetry) records a sample's thermal events across a controlled temperature ramp — melting, recrystallization, glass transition and exothermic or endothermic reactions — pairing each event with a temperature and an associated energy. TGA (thermogravimetric analysis) measures the sample's mass change under the same controlled-ramp logic, revealing water loss, residual solvent or decomposition as a function of temperature.
Together, the two techniques answer complementary questions: DSC identifies what happens thermally to the sample, and TGA explains whether an event observed by DSC is a genuine physical transition, such as melting or glass transition, or is associated with mass loss, such as desolvation or dehydration. That combination is what makes a thermal event's interpretation reliable rather than ambiguous.
Feasibility and study design depend on the analytical question, whether compatibility screening, process-window definition or hydration investigation, and on the quantity and nature of the available sample. The report separates observation, processing and interpretation so the conclusion does not imply greater certainty than the data support.
What thermal events reveal, and why it matters
A single thermal event rarely settles a decision on its own; what matters is what it indicates when interpreted in the right context, with DSC and TGA read together.
| What is observed | What it can indicate | Practical consequence |
|---|---|---|
| API-excipient thermal incompatibility | A new, shifted or suppressed thermal event in a physical mixture of API and excipient, absent in the isolated components. | Can indicate interaction between the components, supporting or ruling out a candidate excipient before committing to formulation development. |
| Safe process window | The temperature at which melting, degradation or significant mass loss begins. | Sets the safe upper limit for drying, granulation or compression operations without compromising the API. |
| Hydrates and solvates | TGA mass loss over a temperature range consistent with water or solvent of crystallization, paired with an endothermic DSC event. | Can explain stability or behavior differences between batches wrongly attributed to a process change. |
| Amorphous content and glass transition | The presence and temperature of a glass transition (Tg), rather than a sharp melting event. | Signals fully or partly amorphous material, relevant to recrystallization risk during storage. |
| Approximate purity via melting-point depression | Broadening or a shift of the DSC melting peak relative to a reference standard. | Can indicate the presence of an impurity or a second phase, to be confirmed by a dedicated quantitative technique. |
DSC and TGA characterize thermal events and mass change; definitively identifying a specific crystalline form generally requires confirmation by X-ray diffraction, treated as a complementary analysis when polymorphism risk is identified.
From technique to decision
DSC and TGA answer complementary questions; reading them together is what supports a robust interpretation, not the isolated result of either technique.
| Technique | What it measures | What decision it supports |
|---|---|---|
| DSC · Differential Scanning Calorimetry | Thermal events such as melting, recrystallization, glass transition and exothermic or endothermic reactions, with the temperature and energy associated with each event. | Whether there is evidence of API-excipient incompatibility, amorphous content, or a transition relevant to the process. |
| TGA · Thermogravimetric Analysis | Mass loss as a function of temperature, associated with water, residual solvent or decomposition of the components. | Whether an event observed by DSC is associated with mass loss, such as desolvation or dehydration, or is a physical transition without mass loss. |
| Hot-stage polarized light microscopy | Visual change in morphology and birefringence across a controlled temperature ramp. | Whether the thermal event recorded by DSC corresponds to an observable phase transition, melting or recrystallization under the microscope. |
The analytical workflow
Every sample runs through the same logical sequence, with temperature range and comparators adjusted to the question; not every study requires all three techniques.
Feasibility screening
Assessment of the analytical question, whether compatibility, process window or hydration, and of the available sample, to define the study design and the relevant temperature ranges.
Feasibility opinion and study design
DSC characterization
Acquisition of DSC curves for the isolated components and, where applicable, physical mixtures, identifying thermal events and their temperatures.
DSC curves with thermal events identified
TGA characterization
Acquisition of TGA curves correlated with the DSC events, to associate each thermal event with any corresponding mass loss.
TGA curves correlated with the DSC events
Interpretation and comparison
Comparison across isolated components, mixtures or batches included in scope, with an explicit discussion of the interpretation limitations the method imposes.
An interpreted report, with limitations stated
Applications
The same combined DSC/TGA reading supports distinct investigations, from pre-formulation through process troubleshooting.
Pre-formulation
API-excipient compatibility screening
Identifying signs of thermal interaction between the API and candidate excipients, before committing development to a specific combination.
Process
Safe process-window definition
Determining the temperature above which drying, granulation or compression begins to compromise the API or the excipients.
Solid state
Hydrate, solvate and amorphous-content investigation
Correlating DSC events with TGA mass loss to characterize the components' solid form, as a layer that complements polymorphism identification by XRD.
Analytical complement
Support for deformulation and polymorphic analysis
A thermal-characterization layer that complements deformulation and polymorphic analysis, when the question is about thermal behavior and stability, not only form identity.
What you receive
An interpreted technical report, not a set of loose curves.
Data and evidence
- DSC curves per component, mixture or batch analyzed, with events identified
- TGA curves correlated with the DSC events, with mass loss by temperature range
- Polarized light micrographs and hot-stage data, where applicable to the scope
- A description of sample preparation and the acquisition parameters used
Interpretation and conclusions
- Identification of thermal events and association with mass loss, where applicable
- An opinion on evidence of thermal incompatibility between API and excipients
- Discussion of process window and amorphous-content or hydration risk, where applicable
- Evidence organized in a format that supports a formulation or process decision
Scope and turnaround
Scope is question-driven: a compatibility screening across a few components is faster than a comparative study across multiple batches or conditions.
- Feasibility screening before any interpretation is promised
- Temperature range and comparators set in the analytical plan, based on the question
- DSC and TGA read together, not as isolated results
- Results expressed as identified thermal events and their interpretation, not as automated classification
- Suited to pre-formulation screening, process-window definition and deviation investigation
Frequently asked questions
What is the difference between this analysis and the general thermal analysis service?
- The general thermal analysis service covers DSC and TGA as standalone techniques, applicable across industries and questions. This analysis is scoped specifically to the pharmaceutical solid-state decision: API-excipient compatibility, process window, and hydrate, solvate and amorphous-content investigation, with DSC and TGA always read together.
What is the difference between this analysis and polymorphic analysis?
- Polymorphic analysis uses DSC and TGA, among other techniques, to identify which specific crystalline form is present, generally with XRD confirmation. This analysis focuses on interpreting the thermal events and mass loss themselves — compatibility, process window and hydration — which often precedes or feeds into a deeper polymorphism investigation.
Does DSC alone identify incompatibility between an API and an excipient?
- A new, shifted or suppressed thermal event in a physical mixture is a lead, not standalone proof. Interpretation weighs the behavior of the isolated components, the design of the tested mixture and, when needed, complementary techniques before supporting an incompatibility conclusion.
What is glass transition (Tg), and why does it matter?
- It is the temperature at which an amorphous material moves from a rigid, glass-like state to a more mobile one, without a sharp melting event. Its presence signals fully or partly amorphous material, relevant to assessing recrystallization risk and property changes during storage.
How does TGA help interpret an event observed by DSC?
- If an endothermic DSC event occurs in the same temperature range as a TGA mass loss, the event is likely associated with water or residual solvent, such as desolvation or dehydration, rather than a genuine physical transition like melting. Without TGA, that distinction is not possible.
Does this analysis define the maximum safe temperature for a drying or granulation process?
- The analysis identifies the temperature at which melting, degradation or significant mass loss begins for the components evaluated, which informs the safe process-window definition. The final process decision also weighs other manufacturing-process variables outside the scope of this standalone analysis.
Can DSC indicate the purity of an API?
- Broadening or a shift of the DSC melting peak, relative to a reference standard, can indicate the presence of an impurity or a second phase. It is an approximate indication, not a quantification; purity confirmation depends on a dedicated quantitative technique.
Which samples can be evaluated?
- APIs, isolated excipients, physical mixtures and finished products may be considered, based on the study question. The amount of sample required and the comparison strategy are defined at the feasibility-screening stage.
How long does a thermal properties study by DSC and TGA take?
- It depends on the number of components, mixtures or batches compared, set after the feasibility screening. Turnaround is set in the proposal, after that initial stage.
Is the information submitted handled confidentially?
- Yes. Scope, samples, results and the existence of the study are treated as client confidential information, under a confidentiality agreement signed before samples are sent.
Services that complement thermal properties analysis
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Scope is question-driven: a compatibility screening across a few components is faster than a comparative study across multiple batches or conditions.
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