Value assignment and uncertainty evaluation for anion and single-element reference solutions incorporating historical...

Area of Science:

• Metrology and Analytical Chemistry
• Reference Material Characterization
• Uncertainty Evaluation

Background:

• The National Institute of Standards and Technology (NIST) certifies mass fractions in single-element and anion solutions using gravimetric and instrumental methods.
• Current uncertainty evaluation includes method-specific, stability, and between-method difference components.
• Historically, between-method differences were based solely on current material characterization.

Purpose of the Study:

• To introduce and justify a new procedure for evaluating between-method differences in uncertainty calculations for certified reference materials.
• To leverage historical data on preparation and measurement methods for improved uncertainty assessment.
• To enhance the overall quality of uncertainty evaluations for NIST standard reference materials.

Main Methods:

• A novel procedure blending historical between-method differences with newly observed differences.
• Utilizes long-standing preparation (40 years) and instrumental (20 years) methods.
• Applies to single-element and anion solutions, including inductively coupled plasma optical emission spectroscopy and ion chromatography.

Main Results:

• The new procedure is expected to yield relative expanded uncertainties approximately 20% smaller than current methods.
• Demonstrates improved quality of uncertainty evaluations by incorporating historical data on method performance and solution stability.
• Historical data shows consistent certified values and uncertainties within comparable solution series.

Conclusions:

• The new blending procedure offers a more robust and accurate method for uncertainty evaluation in certified reference materials.
• Incorporating historical data significantly enhances the reliability of uncertainty assessments over the lifetime of the solutions.
• This advancement improves the quality and precision of NIST's certified reference materials.