A simplified approach to determine the expiration date of certified reference material based on the results of monitoring long-term stability

Abstract

All components of the quality assurance (QA) system for measurement results depend heavily on certified reference materials (CRMs). There is a need for a comprehensive discussion of the stability study using the CRM statistical method. Monitoring involves periodic sampling and analysis of the CRM at predetermined intervals to continuously monitor stability without compromising its integrity. The obtained stability data is then subjected to statistical analysis, considering factors such as trends, variability, and acceptable limits. In this study, we propose a simplified approach as a linear trend to determine the expiration date of CRM. A case study is conducted using the application of the mentioned statistical approaches according to ISO GUIDE 35:2017 with the inclusion of a linear trend for four MODAS CRMs based on the total mercury (THg) content, which all met the positive criteria for each test and CRM. The proposed approach may be helpful when the requirements stated in section B.4.2 (NOTE 3) are not met of the ISO GUIDE 35:2017. Although the shelf-life is an estimated value, it is, therefore, possible to apply simplifications in the course of its determination. The linear trend analysis would serve an ideal role while accessing the long-term stability study of the CRMs.