Inter-Laboratory Analysis Program (ILAP) Program Protocol
Inter-Laboratory Analysis Program
ASTM Standard E691-87, “Conducting an Interlaboratory Study to Determine the Precision of a Single Test Method", outlines a well-considered and logical plan for conducting an Inter-laboratory test program involving multiple analytical techniques. The Analytical Reference Materials International ILAP is managed utilizing the ASTM plan guidelines for planning, sample distribution, sample analysis, protocol and treatment of data results where applicable.
Selection of Participating Laboratories
ILAP membership is voluntary; members include labs for the actual producers of the materials being analyzed, technically qualified commercial laboratories and labs representing general industry and academia.
Materials that emulate alloy types used daily by real-life analysts are typically selected from standard industry stocks. Program materials are secured in a wrought condition whenever possible. Continuous cast, sand or static cast materials are utilized as a last resort only when wrought materials are unavailable.
Most metals are available in bar stock or rod form, so that a typical "batch" or "series" is defined as a single length of material or a single bar of one continuous length.
The "batch" samples are taken by dividing the bar into a minimum of twelve sub-sections. A one inch solid test sample is removed from each sub-section. Each one inch test sample is further subdivided as follows:
- Approximately 12.5% (0.125 in.) of the total sample is converted to chip form for analysis by classical wet chemistry, ICP, AA, and combustion procedures.
- An additional 12.5% (0.125 in.) is converted to solid pin form for determination of C, S, N2 and O2 by combustion procedures, when appropriate.
- The remaining 75% (0.75 in.) of each sample remains in a solid disk form for Optical Emission and X-Ray analysis where applicable.
Each chosen Inter-Laboratory Analysis Program member lab receives the three sample types from a single batch sample, and is therefore responsible for that specific sub-section of the batch bar. All sub-sections and their corresponding test samples are sequentially marked with unique and matching internal identification numbers, so if sample abnormalities appear during the ILAP process, each test sample can be traced to its correct sub-section. This extensive sampling procedure allows that homogeneity of the total batch is therefore reflected as a product of the overall statistics and the resulting certified data.
Specific Within-Sample Determination of Homogeneity
Effective with materials certified after 10/20/91, specific homogeneity testing is determined by the ILAP program management, and incorporates homogeneity test procedures as outlined in ASTM E-826-87, NBS Handbook 91, "Experimental Statistics" and incorporates other established practices for determination of practical homogeneity.
Methods of Analysis
The Inter-Laboratory Analysis Program encompasses the analysis of an extremely wide variety of materials. No single analytical method would provide optimum data results for all elements in all samples. Therefore, a combination of techniques that include classical wet chemistry, ICP, AA, Optical Emission and X-Ray spectrometric methods are used to generate analytical data. Additionally, combustion techniques are used for the determinations of Carbon, Sulfur, Nitrogen and Oxygen.
Extent of Data Reported
It is the policy of Analytical Reference Materials International to report data submitted by two or more labs. However, in accordance with the guidelines established by the ILAP membership protocol, final certification occurs only for those elements in which a minimum of six data points remain after final critique. Therefore, data in parentheses ( ) is not certified but is provided for information only. Certified Data that was selected by the ILAP membership for additional testing is indicated by brackets [ ].
ILAP management approaches traceability to NIST values in two distinct ways:
- SRMs produced by the National Institute of Standards & Technology (NIST) are selected on a "best available/matrix compatible" basis. ILAP management removes the NIST identification, converts portions of the solids to chip form and re-labels both the solids and the chips with unique Analytical Reference Materials International identification. These materials are then submitted to ILAP members as "unknowns" for analysis at Analytical Reference Materials International expense. The resulting data from this procedure is compiled, statistically evaluated and archived in the historical database.
- Specific SRMs are not always available for all matrix groups. Frequently the ILAP program members help to fill these gaps by voluntarily making a variety of NBS/NIST SRMs available to the ILAP, some of which have been collected over a period of almost two decades. These resident SRMs are used to augment calibration curves for that portion of the ILAP which requires instrumental analysis, and to validate test methods and instrument performance where possible. ILAP member labs' SRM inventory and their applications are archived in the Analytical Reference Materials International historical database. The IARMs developed under this program, therefore, have analytical data results that are "Traceable" to values supplied by the U.S. Department of Commerce, National Institute of Standards & Technology (NIST). The specific SRMs applicable to a certification are referenced on the face of the "Certificate of Analyses" for all ILAP-certified materials.
For more information, or if you are interested in joining our program, please contact us at ILAP@ARMI.com.