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Sensitivity of analytical methods - LOD/LOQ
Dec 16, 2020 | Published by Chris Allen
Broughton Chief Scientific Officer, Chris Allen, discusses the sensitivity of analytical methods appropriate for Toxicological assessment of ENDS aerosol.
In order to conduct robust health risk assessments in support of your regulatory submissions, the sensitivity of the analytical methodology is of paramount importance. It’s easy to assume that Pharmaceutical standards are the most stringent of all, for example the application of ICHQ3D for elemental impurities. The levels stipulated in ICHQ3D for chromium are based upon the toxicity of Cr(0) and Cr(III), on the basis of these being the most abundant metallic forms in pharmaceuticals. The toxicity of Cr(VI) is excluded from the safety assessment used to define the permitted daily exposure (PDE) levels for chromium. It is noted that if Cr(VI) is used as a catalyst, the assessment should incorporate this form by assessing the available data. In the case of ENDS, chromium is often found in generated aerosols, but the valence state is not indicated.
The assessment of such metals may require a different approach in tobacco products, depending on the regulatory framework. For instance, when demonstrating that your product is appropriate for the protection of public health (APPH) for a US FDA premarket tobacco product application (PMTA), data related to Cr(VI) is important to incorporate. The US FDA classifies chromium as a harmful and potentially harmful constituent (HPHC) listed as carcinogen, respiratory toxicant and reproductive and developmental toxicant. Cr(0) and Cr(III) are not considered carcinogenic, however Cr(VI) is a classified carcinogen. To address the cancer endpoint as stipulated by FDA in association with chromium, the risk assessment will utilize a guidance value for Cr(VI). In addition, research has highlighted the potential for oxidization of Cr(III) into carcinogenic Cr(VI) at the cellular level, and therefore conducting the risk assessment using guidance values for Cr(VI) provides a conservative approach unless the analytical method has the capability to separate out the covalent species. Direct injection ICP-MS or ICP-OES are often used for the analysis of metals. As these techniques alone do not distinguish between the oxidation states, the application of the medicinal PDE levels do not provide the required sensitivity, therefore you must be able to reliably detect and quantify in the region of 100 times lower than the recognized pharmaceutical standards.
When developing methodology for the analysis of ENDS, the desired sensitivity of the method must be defined from the outset so that appropriate toxicological risk assessments can be performed using the relevant guidance values and so the data can be contextualized in comparison to other marketed tobacco products (including other ENDS products and combustible cigarettes for example). Broughton in-house toxicology team perform regular literature reviews to identify new research which may highlight new potential health risks. Working in conjunction with the Chemistry team, ensures that methodology is constantly reviewed and updated to ensure it is fit for purpose to conduct the necessary risk assessments dependent on the regulatory framework.
Limit of Detection
It is also important to be aware that limits of detection and quantification are often detailed as to what the analytical measurement system can achieve. The limit of quantification of the method itself takes not only the instrument capability into consideration, but it also must be proven the method is accurate, linear and precise at this level. This assessment must be in the presence of the sample media (e.g. e-liquid), which often creates interferences even when using highly sensitive and specific techniques such as LCMS or GCMS, due to suppression caused by the ratio of ingredients in comparison to the low target level of analyte (often ppb or lower). You must also demonstrate that any aerosol collection techniques can satisfactorily capture and retain the analyte across the range of the method, i.e. no significant breakthrough or degradation of the analyte.
Although you may initially be pleased to see your HPHC data reported as ‘Below Limit of Detection’, you must consider carefully if the method is fit for purpose for performing risks assessments and has been validated appropriately. If you don’t perform this assessment yourself, you may find the regulators will do this on your behalf and challenge the appropriateness of your risk assessment outcomes.
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