ASTM D6299 Evaluate Analytical Measurement System Performance
ASTM D6299 Standard Practice for Applying Statistical Quality Assurance Techniques to Evaluate Analytical Measurement System Performance
6. Reference Materials
6.1 QC samples are used to establish and monitor the precision of the analytical measurement system.
6.1.1 Select a stable and homogeneous material having physical or chemical properties, or both, similar to those of typical samples tested by the analytical measurement system.
NOTE 4 - When the QC sample is to be utilized for monitoring a process stream analyzer performance, it is often helpful to supplement the process analyzer system with a subsystem to automate the extraction, mixing, storage, and delivery functions associated with the QC sample.
6.1.2 Estimate the quantity of the material needed for each specific lot of QC sample to (1) accommodate the number of analytical measurement systems for which it is to be used (laboratory test apparatuses as well as process stream analyzer systems) and (2) provide determination of QC statistics for a useful and desirable period of time.
6.1.3 Collect the material into a single container and isolate it.
6.1.4 Thoroughly mix the material to ensure homogeneity.
6.1.5 Conduct any testing necessary to ensure that the QC sample meets the characteristics for its intended use.
6.1.6 Package or store QC samples, or both, as appropriate for the specific analytical measurement system to ensure that all analyses of samples from a given lot are performed on essentially identical material. If necessary, split the bulk material collected in 6.1.3 into separate and smaller containers to help ensure integrity over time. (Warning - Treat the material appropriately to ensure its stability, integrity, and homogeneity over the time period for which it is to stored and used. For samples that are volatile, such as gasoline, storage in one large container that is repeatedly opened and closed can result in loss of light ends. This problem can be avoided by chilling and splitting the bulk sample into smaller containers, each with a quantity sufficient to conduct the analysis. Similarly, samples prone to oxidation can benefit from splitting the bulk sample into smaller containers that can be blanketed with an inert gas prior to being sealed and leaving them sealed until the sample is needed.)
6.2 Check standards are used to estimate the accuracy of the analytical measurement system.
6.2.1 A check standard may be a commercial standard reference material when such material is available in appropriate quantity, quality and composition.
NOTE 5 - Commercial reference material of appropriate composition may not be available for all measurement systems.
6.2.2 Alternatively, a check standard may be prepared from a material that is analyzed under reproducibility conditions by multiple measurement systems. The accepted reference value (ARV) for this check standard shall be the average after statistical examination and outlier treatment has been applied.
6.2.2.1 Exchange samples circulated as part of an interlaboratory exchange program, or round robin, may be used as check standards. For an exchange sample to be usable as a check standard, the standard deviation of the interlaboratory exchange program shall not be statistically greater than the reproducibility standard deviation for the test method. An F-test should be applied to test acceptability.
NOTE 6 - The uncertainty in the ARV is inversely proportional to the square root of the number of values in the average. This practice recommends that a minimum of 16 non-outlier results be used in calculating the ARV to reduce the uncertainty of the ARV by a factor of 4 relative to the measurement system single value precision. The bias tests described in this practice assume that the uncertainty in the ARV is negligible relative to the measurement system precision. If less than 16 values are used in calculating the average, this assumption may not be valid.
NOTE 7 - Examples of exchanges that may be acceptable are ASTM D02.CS92 ILCP program; ASTM D02.01 N.E.G.; ASTM D02.01.A Regional Exchanges; International Quality Assurance Exchange Program, administered by Alberta Research Council.
6.2.3 For some measurement systems, single, pure component materials with known value, or simple gravimetric or volumetric mixtures of pure components having calculable value may serve as a check standard. For example, pure solvents, such as 2,2-dimethylbutane, are used as check standards for the measurement of Reid vapor pressure by Test Method D5191. Users should be aware that for measurement systems that show matrix dependencies, accuracy determined from pure compounds or simple mixtures may not be representative of that achieved on actual samples.
6.3 Validation audit (VA) samples are QC samples and check standards, which may, at the option of the users, be submitted to the measurement system in a blind, or double blind, and random fashion to verify precision and bias estimated from routine quality assurance testing.
