Phys-Chem and Storage Stability Testing for Biocidal Products

Phys-Chem and Storage Stability Testing for Biocidal Products

At the recent Dublin Biocides Symposium organised by Kerona Scientifc, David Norris, owner of DNAL (David Norris Laboratories in the UK) gave a presentation on Phys-Chem and Storage Stability Testing for Biocidal Products.

Storage stability testing includes physical tests and active substance analysis, to ensure that the product is still useful after storage. It is important to use the same batch for the various parameters both before and after storage to ensure that you are testing like for like. Besides the ECHA guidance on the BPR Volume I, Version 2.0 May 2018 it may be useful to refer to the plant protection guidance SANCO/10473/2003 – rev. 5 which gives further information on some of the physical tests. GLP laboratories are preferable for testing as they are highly regulated, and all steps are controlled. If a change to the testing is required after the GLP study plan (protocol) is finalised, it will be necessary to prepare an amendment to the study protocol. On completion of the study a draft report is authored. This is the opportunity to make any required changes, as once the final report is agreed and issued, any required changes can only be done through amendments to the report. The finished report is then archived for the purposes of GLP.

Some very important tips were given in the presentation:

• Very carefully consider the expected lifespan of the active substance before launching into a 2-year shelf-life as additional timepoints may be required based on the known instability of the compound (e.g., for sodium hypochlorite)
• Validation requirements differ worldwide, therefore it is strongly advised to take the planned sales locations into consideration when communicating with the lab about planned tests.
• Accelerated storage stability can mitigate the 2-year shelf-life by imitating and predicting possible issues however, some compounds can be problematic in accelerated storage. For example, the high temperatures of 54°C are not suitable for some alcohols due their low boiling point leading to higher vapour pressure that can lead to sample loss in unsuitable containers

With regards to method validation, the BPR requirements have been based on SANCO 3030/99 rev 4 (although plant protection guidance has moved on from this). Methods used for registration purposes need to be specific, for example, titration is not suitable as it is not specific (many chemicals could produce the same colour change). It is also important to choose the appropriate detection method based on your chemical. One of the most widely used techniques, HPLC-UV, which is very suitable for chromophore groups with delocalisation of electrons (e.g., benzene rings) cannot be used for some biocide substances, e.g.  DDAC which has no double bonds therefore HPLC-ELSD is used instead. When it comes to analysis of alcohols, GC is popular, however the reproducibility often does not meet the strict guidance requirements, so this is more challenging than expected for such simple compounds. Polymeric structures are problematic as the focus of the analysis guidance has been on small molecules. As an example, for analysis of Zineb the CIPAC has presented a method based on acid digestion and capture of carbon disulfide which is then analysed using GC-MS (not titration!).

If you require assistance with study commissioning of your phys-chem and analytical studies for biocidal products, please do not hesitate to get in touch with Kerona’s biocide regulatory team at info@kerona.ie or give us a call at +353 (0)1 849 5284