About the ilap process

Sterling’s Inter-Laboratory Analysis Program (ILAP) is a voluntary collaboration among industry producers, academic departments, and commercial testing laboratories committed to ensuring the availability of high-quality reference materials. The program applies multiple analytical techniques to real-world matrices, supported by statistical evaluation and traceability to national metrology institutes. The assigned values are consensus-based and are supported by statistically valid interlaboratory data. The success of ILAP is made possible through the dedicated work of these cooperating laboratories.

ILAP emphasizes:

• Metrological traceability to NIST or other national  metrology institutes (NMIs).
• Use of real-matrix candidate materials representative of intended use.
• Use of validated measurement  procedures and competent laboratories.
• Robust statistical evaluation, including appropriate  inclusion/exclusion criteria for data treatment.
• Transparent technical justification for all decisions affecting assigned values.

ILAP Workflow Summary

Step 1 – Initial Testing 

Labs receive two bottles of candidate material, analyze (preferably in triplicate), and submit results. Data may be reported using Sterling’s provided templates or the lab’s own reporting format. Sterling screens data for outliers (numerical or methodological) and requests re-runs where appropriate. Screening methods may include:

• Robust mean estimation techniques
• Grubbs/Cochran-type outlier tests
• Between-laboratory precision assessments
• Evaluation of method-specific effects
• Assigned value determination and associated standard uncertainties

Step 2 – Secondary Evaluation and Consensus Value Development

A second round of results are generated based on the refined data sets.

Consensus values are established based on datasets that satisfy ILAP’s acceptance criteria for accuracy, precision, consistency, and traceability. The same screening methods used in step 1  are used in the second round of evaluation.

Step 3 – Review of Excluded Data 

Sterling provides formal notification to any laboratory whose data is excluded from the final dataset.

Exclusions are supported by objective, statistically defensible justification, consistent with ISO Guide 35 guidance on data treatment.

Laboratories may initiate technical dialogue to review exclusion rationale, provide additional method information, or defend measurement validity. This step ensures transparency and minimizes methodological bias in the characterization process.

Step 4 – Certification 

After reconciliation of all data discrepancies, Sterling finalizes the consensus dataset and assigns the certified value(s) along with associated combined and expanded uncertainties in accordance with ISO 17034 and the GUM (Guide to the Expression of Uncertainty in Measurement).

A formal Certificate of Analysis (CoA) is then issued, containing:

• Assigned values
• Uncertainty statements
• Traceability declarations
• Measurement and method information
• Relevant stability and  homogeneity considerations

As part of ILAP’s collaborative framework, and as a thank you, participating laboratories are provided additional units of the newly certified CRM and updated labels for previously supplied candidate materials.