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Certified Reference Materials (RESL’s Accreditation). Guy Backstrom ASP 2012 Workshop Idaho Falls, Id 9/18/2012. DISCLAIMER.
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Certified Reference Materials (RESL’s Accreditation) Guy Backstrom ASP 2012 Workshop Idaho Falls, Id 9/18/2012
DISCLAIMER • The slides in this presentation contain a lot of information and all of it can’t be discussed in the allotted time. However, these slides were intentionally left in the presentation for later review by the attendee.
Background: Laboratory Quality • 1950-80’s Laboratory Quality was mostly defined as being able to get the right answer running single blind Quality Control Samples with a batch of unknown samples being analyzed. • The definition of Quality began changing in the 80’s to also include a system that formally corrected problems and controlled documented procedures. • By the 90’s the concept of Laboratory Quality also included preventative actions. • 2000 onward, Laboratory Quality also includes customer feedback and complaints.
Background: RESL’s Quality System • 2001 – RESL’s Quality System that had was based on NQA-1 had been revised to meet the requirements in ISO 17025. • 2001-2002 RESL’s staff were formally trained to the requirements of ISO 17025, procedures were rewritten to meet the requirements. • 2002 Preliminary ISO 17025 audit, conducted by independent experts, to find out where RESL was. • 2002-2003 RESL applies and receives ISO 17025 accreditation through the American Association of Laboratory Accreditation (A2LA). • 2007 RESL applies and receives accreditation to ILAC G13 as a performance testing provider by A2LA. • 2011 RESL applies and receives accreditation to ISO Guide 35 as a Reference Material Provider by A2LA.
Background: RESL’s Quality System • RESL has been making radiological standards for over 40 years and inorganic standards for over 15 years. • RESL’s standards are mostly used to assess Laboratory performance. • RESL also prepares standards used for calibrations. • RESL has established radiological intercomparision programs for over 30 years with NIST. • 1999 - RESL staff began formal Quality training through weekly internal seminars. • 2000 – RESL management decided that a Quality system based on ISO 17025 – Competency of a Chemical Testing Laboratory – was the path that should be taken.
RESL’s ISO Guide 35 Accreditation • Purpose of CRM accreditation: To ensure that valid methods are established to assign values to properties of a reference material, including the evaluation of their associated uncertainty, and establish their metrological traceabliity. • Reference material that undergo all steps described in ISO Guide 35 are usually accompanied by a certificate and are called certified reference materials (CRM).
Why CRM accreditation • “In order to be comparable across borders and over time, measurements need to be traceable to appropriate and stated references. CRMs play a key role in implementing the concept of traceability of measurement results….”. • ISO Guide 35 explains how methods can be developed that will lead to well established property values, which are made traceable to appropriate stated references. • RESL agrees with the concepts of ISO Guide 35 and becoming accredited to ISO Guide 35 completes the circle for the products that RESL produces. • ISO 17025 for analyses, ILAC G13 for Performance Testing, ISO Guide 35 for the materials produced for Performance Testing.
The big three that tend to be overlooked • Homogeneity • Within Bottle For Subdivision • Between Bottle • Batch Produced • Batch Produced (Individuals) • “Single Shot” • Stability • Transportation • Shelf-Life
RESL’s Approach to Homogeneity • RESL produces reference material that is homogeneous and stable from the time of production until the indicated expiration date is reached. • The reference material is also homogeneous and stable during storage and shipment to the customer. • The homogeneity of the reference material refers to both the within-sample and between-sample homogeneity of the material when samples can be subdivided. • Within-sample inhomogeneity is not relevant when the entire sample is taken for analysis.
RESL’s Approach to Homogeneity (Soil) • To demonstrate the homogeneity of soil reference material, 10 samples using duplicate 1 gram aliquots from each bottle are selected and all analytes of interest are analyzed according to The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry Laboratories. • In accordance with The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry Laboratories, RESL uses the F1 value of 1.88 and F2 value of 1.01 from Table 2 in Appendix 1 for homogeneity testing of soils. • The radiological analytes in the soil reference material are evaluated for homogeneity using a 3% target concentration uncertainty with no more than a 5% total variation between samples. • The inorganic analytes in the soil reference material are evaluated for homogeneity using a 5% target concentration uncertainty with no more than a 10% total variation between samples.
RESL’s Approach to Homogeneity (Liquid) • The liquid reference materials that RESL produces are composed of stabilized analytes added to a compatible, stabilized matrix. • Under these conditions liquid reference materials are inherently homogeneous and within-sample inhomogeneity has never been observed. • RESL verifies the reference values to ensure that there were no undetected problems during preparation of the liquid reference material. The verification of the reference values on liquid reference material is made with uncertainties of approximately 3%.
RESL’s Approach to Homogeneity (Non-Subdividable) • SINGLE SHOT - BOMAB and Thyroid Phantoms are produced using the same process discussed in the liquid section and exhibit the same inherent homogeneity as other liquid reference materials. Lungs, BOMAB and Thyroid Phantoms are non subdividable and the reference values are verified through replicate non destructive measurements. • BATCH PRODUCED -non subdividable reference materials include air filters, vegetation, fecal and urine samples. The individual samples in a batch are spiked sequentially and a systematic sampling is taken for non destructive analysis of indicator analyte(s) to ensure consistency across the batch.
RESL’s Approach to short-term stability (Transportation) • Transportation stability was accomplished by subjecting 10 liquid and 10 soil reference material samples, in their original containers, to the temperature extremes expected in the duration of an international shipment and measuring the weight of the bottle prior to heating and post heating at various time intervals for up to 7 days. Weight loss of the liquid and soil reference material was less than 0.05% and 0.3%, respectively, and is considered negligible and does not affect the reference value at these extreme conditions. • RESL used the US Military worst case assumption of 160° F (71° C) as the extreme temperature that the samples would be exposed to.
RESL’s Approach to short-term stability (Transportation) • RESL took 10 MAPEP water samples and subjected them to a temperature of minus 30°C for 7 days. These samples were brought back to room temperature and the top 200mL of 4 non-disturbed and 4 shaken samples were analyzed. The 4 non-disturbed samples had results for the indicator analytes ranging from minus 30 to minus 70% of the known reference values due to stratification. • The 4 shaken samples had results for the indicator analytes that were statistically identical to the reference values. • Instructions are now included to shake liquid reference material before use. DOELAP Assessor Training
RESL’s Approach to short-term stability (Transportation) DOELAP Assessor Training
RESL’s Approach to long-term stability (Shelf-Life) • RESL evaluated the long-term stability of a variety of reference materials produced over a period of 10 years and stored under normal laboratory conditions. • These samples were analyzed to verify that the reference value for each analyte had not changed over time. • Long term stability of the radiological isotopes was evaluated following ANSI N42.22 guidance. • The ratio of the measured value to the reference value and the total propagated uncertainty are calculated. If the ratio plus or minus three times the total propagated uncertainty is statistically identical to unity, then the experimental value is statistically identical to the known value and the analyte was considered stable for that time period.
RESL’s Approach to process stability • RESL evaluated the process stability of the radiological isotopes by performing a linear regression of the ratio of the experimental result to the known value over multiple batches. • The absolute value of the slope of the regression line was compared to the uncertainty of the slope of the regression line multiplied by the Student’s-t factor for n-2 degrees of freedom at the 95% confidence interval. • If the absolute value of the slope of the line was less than the uncertainty of the slope multiplied by the Student’s t-factor then the change in the reference value was considered insignificant and stability was achieved for the maximum time for which the samples had been stored.
