The earliest sign of degradation
Many active ingredients, excipients and formulations degrade through chain reactions in which radicals are formed. Chemical analysis finds the degradation products later. EPR (electron paramagnetic resonance) sees the radicals themselves, so it shows when degradation begins, and how well an antioxidant, a light barrier or a packaging choice delays it.
A well-protected product keeps radicals away for a long time under stress. The time before radicals start to build up, the lag time, is a measure of its stability.
Where it is used
- Active ingredients and excipients, including polymers and surfactants
- Liquid and semi-solid formulations
- Creams and topical products
- Packaging materials and their effect on the contents
Surfactants such as the polysorbates used to stabilise protein medicines are a good example: they oxidise through radical chains, and a spin trap shows how quickly this happens under forced conditions. Typical tasks are stress testing a formulation, ranking antioxidants, comparing packaging or light protection, and screening raw materials.
Catching radicals so they can be counted
Radicals live only for a moment, far too briefly to be measured. A spin trap is added to the sample. It reacts with the radicals and forms a stable compound that lives long enough to be measured. The height of the signal is the amount of radicals trapped, and the pattern of lines identifies the kind of radical.
The sample is aged under controlled stress, for example at a raised temperature or under light, and measured at regular intervals. The lag time of each formulation is read from the curve, and formulations can be ranked.
What it adds
- Sees radicals directly, before degradation products are measurable
- A small sample is enough
- Works on coloured and turbid samples
- Forced ageing shortens the wait compared with real-time stability studies
- Benchtop instruments make the technique practical in a development laboratory
Points that matter in practice
- The stress conditions should resemble real storage, so they are chosen and checked for each product
- The spin trap and the conditions are matched to the type of sample, and results are compared only within the same method
- The link between the lag time and the real shelf life has to be established for your own product
- EPR complements the usual stability tests and does not replace them
- EPR detects unpaired electrons only, so it says nothing about degradation that does not involve radicals
From your product to a routine method
Send or bring representative samples. MSY Consulting runs feasibility measurements, defines the stress conditions and the spin trap with you, helps you relate the results to your stability data, and trains your team until the measurement is part of your routine.
Let's talk about your application
Send an email describing your instrument and your application, and you will get a reply.
contact@msyconsulting.euMSY CONSULTING SAS · Wissembourg, France · LinkedIn