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Table of Contents:
TA Tip
- Crucibles in thermal analysis
New in the sales program
- New ceramic sensor (FRS5)
- STARe SW V5.0
- New crucibles
- Thermoplastics handbook
Applications
- Shelf-life of drugs
- TG-MS coupling
- Calcium sulfate measurement
- Determination of vinyl acetate content using thermogravimetry
- PET, physical curing in TMA
The use of thermal analysis to estimate shelf-life of drugs
Active components of drugs are usually not thermally stable. Even when stored at ambient temperature, drugs undergo various chemical changes that influence their pharmaceutical activity. It is therefore important to know the shelf-life (the time during which a drug preserves its activity) of drugs. Directly evaluating shelf-life requires a drug to be kept in a thermostat at slightly elevated temperatures (30-40°C) for several months. An analysis of samples taken at intervals permits the composition of a drug to be monitored. Under the assumption that the pharmaceutical activity is an immediate function of the concentration of an active drug component, shelf-life may be estimated as the time to reach some critical concentration. While capable of providing reliable values of shelf-life, direct evaluation is a costly and time-consuming procedure.
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TG-MS coupling
Evaporation or decomposition effects are observed when many materials are heated or conditioned. These effects can be detected with DTA, DSC or TGA. Unfortunately, these measurement techniques provide no information on which products or fragments are formed, information which would be very useful in many situations.
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Calcium sulfate measurement
We are pleased to be able to show you a completely new high temperature TGA/SDTA curve. Measurements were performed in the temperature range 1000 to 1600 ° C (Fig. 10). Sample preparation: The anhydrite was prepared from the dihydrate (Fluka 21 245) by heating to 500 ° C in a furnace for 10 min.
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Determination of the vinyl acetate content by TGA
Principle
Vinyl acetate, VAc, decomposes between 200 °C and 400 °C with loss of acetic acid (Fig. 11). This degradation step can be used to calculate the VAc content in copolymers (EVA types) provided the sample shows no additional weight loss in this temperature range (e.g. water loss from Al(OH)3 ).
The sample is heated continuously to 850 °C. Adsorbed moisture is removed up to 200 °C . Loss of acetic acid occurs between 200 and 380 °C and thermal destruction of the residual polymers between 390 and 500 °C . From 600 to 850 °C any carbon residues or carbon black are combusted in oxygen. Fillers are found at 850 °C in the form of oxidic residues.
With pure EVA copolymers without fillers, the temperature range up to 600 °C should suffice in most cases.
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PET, Physical Curing by Dynamic Load TMA
Sample
Disk of polyethylene terephthalate (Mettler-Toledo tutorial kit)
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