Dynamic Vapour Sorption
Dynamic Vapour Sorption (DVS) is a gravimetric technique that measures how quickly a sample absorbs a solvent vapour, and how much solvent in total is absorbed. In most cases water vapour is used for DVS experiments, but this can also be performed using a variety of organic solvents if required.
Key Benefits of DVS
- Ultra-sensitive microbalance detects changes in mass smaller than one part in ten million, allowing very small samples to be used and minimising analysis time
- Allows determination of upper and lower humidity limits for storage of your product
- Reveals reversible and permanent changes in materials caused by increased humidity
- Used for quality control of foodstuff and chemical powders during production
- Can be used to evaluate suitability of packaging materials for storage of your dry product
- Allows calculation of surface area of samples – useful when studying porosity or reconstitution behaviour, and for batch comparison purposes
How the analysis is performed
This measurement is achieved by varying the vapour concentration surrounding the sample and measuring the change in mass that this produces. We perform this analysis using our DVS Resolution instrument from Surface Measurement Systems. In our standard analysis procedure the instrument is used to measure the amount of water that is absorbed by the sample when exposed to air at a range of humidity levels, typically from 0% to 90% relative humidity. We then measure the amount of water that is lost when the humidity level is decreased from 90% to 0%. The process can be repeated one or more times to investigate changes in behaviour which are affected by the material’s history.
DVS analysis is used to study the absorption and desorption of water vapour (or organic solvent vapour) occurring in a sample when exposed to a range of humidity levels, typically stepped up from 0% to 90% RH and down again. This process is usually then repeated to look for irreversible changes.
This testing can give useful information about the effects of specific humidity levels on a material, which could include non-reversible changes such as crystallisations and pore collapse, and reversible changes such as hydrate formation. It can also be used to evaluate the suitability of a container for storage of freeze dried materials, by measuring the permeability of a sample of the container material to water vapour.
Our typical method
Our standard procedure includes ramping the chamber humidity up from 0% to 90% RH and down again in steps at every 10% RH. At each step, the humidity is held until the sample weight stabilises. These ramps are then repeated once to test for irreversible changes. If appropriate, we can also take a series of pictures throughout the analysis. Typical analysis time is up to 72 hours, but this can vary significantly depending on the hygroscopicity of the sample, the porosity, and a number of other factors. If analysis time exceeds 96 hours we will contact you to discuss your options, which may include adjustment of the method to accelerate the analysis, or a surcharge to cover the additional analysis time required.
Differential scanning calorimetry
Differential scanning calorimetry (DSC) is a technique used to measure temperature and heat flow associated with thermal transitions in a wide range of materials. During DSC analysis, the sample temperature is raised at a constant rate by heat input. The heat flow required to maintain this constant rate is then logged against temperature to generate the DSC trace, which as a result, shows exothermic and endothermic events.
Some of the most critical events in pharmaceutical freeze drying analysis are glass transitions, both dry state (Tg) and frozen state (Tg’). These apply to amorphous sample components, and are thermodynamically reversible changes that result in a shift in the specific heat capacity of the sample. These indicate a reorientation between amorphous and crystalline regimes and are often highly influential on a number of characteristics of the sample structure. The glass transitions are also visible as a change in the gradient of the DSC trace.
Through the DSC analysis, our service measures the glass transitions, crystallisation and melting events. From a temperature control range of -180°C to +450°C, this enables a wide variety of experiments and applications with a standard 2L liquid nitrogen dewar providing cooling for several hours. Our analysis is highly sensitive allowing for the study of thermal transitions at low heating rates, or with small sample sizes, with no loss of sensitivity.
One of the most important benefits of the DSC analysis is that it includes the ability to be mounted on an imaging station for visual degradation analysis and TASC (Thermal Analysis by Surface Characterisation) during DSC experiments through a sapphire window. Visually observing the physical changes that the DSC trace is quantitatively reporting can be of great benefit, especially for troubleshooting. These images can be made into videos by the software, exported easily with a data ribbon and annotated. An optically sealed crucible is also available for those wishing to conduct closed experiments.