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Pharmaceutical Technology > Thermal Analysis > Flashcards

Thermal Analysis Flashcards

1
Q

What is the meaning of melting point (Tm)?

A

The temperature at which the pure liquid and solid co-exist in equilibrium at 1Atm pressure

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2
Q

What is ‘the latent heat of fusion’?

A

The amount of heat required to melt a material by breaking bonds

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3
Q

What is polymorphism?

A

The same molecule having different solid-state structures (diamond and graphite).
Polymorphs have different crystal lattice energies but are chemically identical.
Polymorphs have different solubilities, dissolution rate and bioavailability.

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4
Q

What is the issue with polymorphism in drug development?

A

*must be sure drug stays in one form throughout whole shelf life
*undesirable polymorph may be toxic
*issues scaling up I.e methods of preparation may change- different solvents, heat generated

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5
Q

What are examples of drugs exhibiting polymorphism?

A

*carbamazepine
*paracetamol
*ampicillin

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6
Q

What excipients exhibit polymorphism?

A

*sorbitol
*lactose

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7
Q

What does it mean if a drug is enantiotropic?

A

The two different forms of the drug have a definite transition point and can change reversibly into one another. At a key temperature, the form stable at low temperatures can convert to high temperature form.

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8
Q

What is a monotropic drug?

A

When one form is more stable at all temperatures. Unstable polymorph will have a lower Tm. Upon heating no transition is observed.

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9
Q

What is a solvate?

A

Crystal lattice of polymorph also contains solvent molecules (eg water)

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10
Q

What is the characteristic transition of amorphous materials ?

A

The glass transition Tg. Below Tg= hard and brittle. Reaction is slow. Above Tg=soft and rubbery. Reaction is faster

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11
Q

What are amorphous materials?

A

Material that has structure of a liquid but mobility of a solid. They have no melting temperature because have no crystal lattice to be broken.

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12
Q

What is DSC?

A

Stands for differential scanning calorimetry. It is a thermal analysis method. Measuring heat output and comparing between reference and sample.

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13
Q

What are the two types of DSC?

A

*Heat flux DSC-direct comparison of reference and sample in same furnace
P= (Ts-Tr)/Rt
p=power
Ts=samaple temperature
Tr=reference temperature
Rt=resistance applied
Power (output of DSC in J/s)
*Power compensation DSC-two separate furnaces

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14
Q

What metal is used to calibrate DSC?

A

Indium

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15
Q

What does MTDSC stand for?

A

Modulated temperature differential scanning calorimetry

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16
Q

Benefit of using MTDSC

A

Easier to observe Tg

17
Q

Why do we need to know Tg?

A

To ensure drug is not stored above Tg causing it to crystallise and increase degradation.
Also to control water content (water lowers Tg as it is a plasticiser)-product must be dry enough to exhibit reasonable Tg yet retain water for structure.

18
Q

Does lowering Tg (increasing water) increase or decrease stability ?

A

Decrease

19
Q

How is glass transition measured?

A

Thermo Gravimetric Analysis (TGA)
*sample heated in controlled manner
*mass loss=water loss
*mass change determined by null-balance principal

20
Q

What is the difference between TGA and Karl Fischer titration?

A

*Sample size can be smaller
*Faster

21
Q

What is microcalorimetry?

A

Measuring heat in or out of a sample at isothermal temperature (constant temp)

22
Q

What is thermomechanical analysis (TMA) used for?

A

*measure dimensional changes in materials (as a function of temp, time isothermally)
*to determine thermal expansion coefficients
*%expansion/contraction
*phase transitions eg Tg

23
Q

Disadvantages of TMA

A

Limited to solids I.e unreliable for amorphous materials

24
Q

What materials can be used for TMA?

A

*stratum corneum (skin)
*braces
*catheters
*intravaginal rings

25
Q

What is DMA?

A

Dynamic mechanical analysis. Used to determine viscoelastic properties of pharmaceutical systems. (Contact lens and heart valves). Stress applied to sample and resultant strain measured as a function of frequency and temperature.

26
Q

What is stress in terms of DMA?

A

Force per unit area (Pa) required to deform the sample.

27
Q

What is strain in terms of DMA?

A

Amount by which sample is deformed. Also known as amplitude (distance)

28
Q

What is modulus in relation to DMA?

A

Resistance of a material to deformation
*storage modulus G’- how much mechanical energy stored in material during deformation recovered when stress released.
*loss modulus G’’-how much mechanical energy lost during deformation (viscosity)

29
Q

What is phase angle in relation to DMA?

A

Phase angle between strain and stress phases (tan§(G’’/G’)

30
Q

What is DMA used for?

A

*measuring glass transitions Tg
*rate and extent of polymeric curing
*polymer compatibility
*interactions between polymeric components
* interactions between drug molecules and polymeric constituents of pharmaceutical systems like catheters

31
Q

Why do we need to know mechanical properties of polymeric systems?

A

*conductance of body fluids (urine)
* prevent rapid release of active agents

Pharmaceutical Technology (21 decks)

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