Estimating the uncertainty of stability for matrix CRMs

Area of Science:

• Metrology and Measurement Science
• Analytical Chemistry
• Quality Assurance

Background:

• ISO Guide 34 mandates the inclusion of instability uncertainty in certified reference materials (CRMs).
• Compliance with the Guide to the Expression of the Uncertainty in Measurement (GUM) is required for CRM uncertainty values.
• Accurate uncertainty estimation is crucial for the reliability of CRMs in various applications.

Purpose of the Study:

• To present a pragmatic approach for estimating the uncertainty associated with the stability of CRMs.
• To provide a method that integrates stability uncertainty into the overall CRM uncertainty budget.
• To demonstrate the applicability of the proposed method to matrix CRMs.

Main Methods:

• Utilizing regression analysis on stability data to assess trends over time.
• Testing the statistical significance of the slope of the regression line to determine stability.
• Estimating stability uncertainty using the standard deviation of the slope when the slope is statistically insignificant.

Main Results:

• The proposed method offers a practical way to quantify the uncertainty contribution from CRM instability.
• Statistical insignificance of the regression slope indicates stability within the defined shelf life.
• The estimated uncertainty due to instability is incorporated into the overall CRM uncertainty calculation.

Conclusions:

• The presented approach provides a robust framework for addressing stability uncertainty in CRMs.
• This method ensures that CRM uncertainty values are compliant with international metrology guidelines.
• The approach is applicable to various types of CRMs, including complex matrix CRMs.