Dissolved gasses in your dissolution media can cause a variety of issues to your run. If not controlled, these gasses can be a source of chaos in your vessels. They can make results higher or lower – but primarily just highly variable. There are a variety of ways to handle dissolved gasses, so let’s discuss the main options!
First, I’ll start with the good news. Not all formulations and methods need degassing! If you can demonstrate that your data is comparable between degassed and non-degassed media in a quick validation, then go for it. In my experience, methods where the media contains surfactant usually don’t need degassing. Modified release formulations are also somewhat less likely to need degassing. Non-disintegrating tends to also need degassing less than disintegrating. Please note these are trends and not absolutes, you need to validate if you don’t want to degas.
The gold standard in degassing is the USP approach. This procedure has you heat the media to 41-45 degrees Celsius, then vacuum degas through a 0.45um PVDF filter, and hold under vacuum for an additional 5 minutes. Why this approach? This is because you are boiling your media under vacuum (remember your Ideal Gas Law, pV-nRT). Unless otherwise stated in your method or SOPs, if you’re degassing – this is the way you degas.
There are other approaches to degassing that can work as well. If you want to use these, you need to validate that either you have comparable results to the USP method OR you measure your approach has <6ppm dissolved gasses. Successful approaches to consider are helium sparging or media degassing systems. I don’t tend to recommend helium for a number of reasons – supply/cost issues of the gas being a main one. If you do use helium, make sure your method specifies a time and flow rate.
A final note – if you need to degas, then you also need to use your media as soon as possible. A de-aerated media will re-aerate! Once you’ve de-aerated and poured your media, then start your run as soon as you’ve reached your temps. This is usually about 10-15 minutes.
Read also: How Do You Choose an RPM in Dissolution?
Resource Person: Ken Boda