1. Consensus Standards, Method Uncertainty and Quality Assurance in Analytical Chemistry Curricula Kevin Ashley, Ph.D. U.S. Department of Health and Human Services Centers for Disease Control and Prevention National Institute for Occupational Safety and Health Cincinnati, Ohio

2. Disclaimer Mention of company or product names does not constitute endorsement by the Centers for Disease Control and Prevention. The findings and conclusions in this presentation are those of the speaker and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

3. Introduction Overview of voluntary consensus standards Overview of voluntary consensus standards What are they & why are they important? What are they & why are they important? QA/QC in analytical laboratory QA/QC in analytical laboratory Need defensible results; verify with QA/QC data Need defensible results; verify with QA/QC data Treatment of analytical method uncertainty Treatment of analytical method uncertainty Vitally important in commercial / gov’t lab Vitally important in commercial / gov’t lab Include ideas in analytical curricula Include ideas in analytical curricula Give students background in aspects that they’ll have to address in ‘real world’ lab. Give students background in aspects that they’ll have to address in ‘real world’ lab.

4. What are voluntary consensus standards? Technical documents developed by consensus: ■ Test methods, specifications, guides, practices, terminology ■ Based on best science for tech transfer: “Research to Practice” “Research to Practice” → Establish standard of care in field (i.e., analysis)

5. Voluntary consensus standards in analytical chemistry Non-profit, non-governmental organizations Global forums for developing voluntary consensus standards (e.g., ASTM International, ISO) Methods/procedures for sampling, sample preparation, analysis, estimation of uncertainty, QA/QC requirements

6. Importance of Standardization Conformity in methods for sampling and analysis Normalized protocols describing laboratory quality assurance / quality control Aim to ensure / maximize data quality, minimize overall analytical uncertainty Provide evidence of acceptable performance

7. Analytical Method Evaluation & Validation Literature Search Analysis Development Sampler Development Method Evaluation Method Evaluation Analyte Recovery Analyte Recovery Sample Stability Sample Stability Limit of Detection Limit of Detection Sample Generation Sampler Capacity Dynamic range Precision & Bias / Uncertainty Interferences Reference materials Field Testing ■ Interlaboratory testing ► Standardization

8. Sampling & Sample Preparation (workplace air)

9. Analytical Method Development Chromatography Chromatography Spectroscopy Spectroscopy Electrochemistry Electrochemistry Bioanalytical chemistry Bioanalytical chemistry Other exs. Other exs.

10. Relative Contributions to Analytical Error Sampling Sample preparation Analysis Significant error Intermediate error Small error Overall (expanded) error = ∑ (individual errors)

11. Quality Assurance/ Quality Control Quality of Sampling and Analytical Method Results Quality of Sampling and Analytical Method Results Quality of results limited by method, analytical laboratory and analyst Quality of results limited by method, analytical laboratory and analyst Method evaluation helps define method performance Method evaluation helps define method performance Analyst and analytical laboratory contribution to quality measured by: Analyst and analytical laboratory contribution to quality measured by: Quality Control Program Quality Control Program → Internal - spiked samples, field blanks, control charts → External - participation in proficiency test programs ► Consensus standards describe these elements, processes & procedures

12. Ex. of an ASTM International standard D7035: Standard Test Method for Determination of Metals and Metalloids in Airborne Particulate Matter by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) Scope Referenced Standards Terminology Summary of Method Significance & Use Apparatus & Materials Sampling Sample Preparation Analysis Expression of Results Method Performance Records Reporting Appendices Annexes References

13. Analytical Method Uncertainty Precision & Bias ASTM International: ASTM E691 – Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method Uncertainty International Organization for Standardization: Guide to the Expression of Uncertainty in Measurement (ISO/GUM)

14. Analytical Precision For n analyses, determine μ, s & RSD (CV) Propagation of random errors: s tot = [s i 2 ] ½ = [s 2 s 2 s 2 s 2 s i’ 2 ] ½ s tot = [∑ s i 2 ] ½ = [s 2 (weighing) + s 2 (pipetting) + s 2 (dilutions) + s 2 (analysis) + s i’ 2 ] ½ Then estimate (95%) CL’s Perform outlier tests (etc.) → For estimation of overall method precision, also include estimate of contribution to error from sampling

15. Limits of Detection and Quantitation LOD LOQ Analyte conc. 95% Confidence Limits Calibration Line Response

16. Analytical Bias B i = (μ i – R i ) R i -1 B i = (μ i – R i ) R i -1 Estimate by comparison of measured results against reference analytical method Estimate by comparison of measured results against reference analytical method Estimate by analysis of reference materials Estimate by analysis of reference materials Is bias negligible?; ideally <<10% (+ or –) Is bias negligible?; ideally <<10% (+ or –) Is bias correctable or not? Is bias correctable or not? Is cause of systematic error identifiable and, if so, does corrective action ameliorate the problem Is cause of systematic error identifiable and, if so, does corrective action ameliorate the problem Consider contributions to bias from steps preceding analysis (e.g., sampling errors, stability & transport) Consider contributions to bias from steps preceding analysis (e.g., sampling errors, stability & transport)

17. Uncertainty “Type A” evaluation: u = s/√n Applicable when n repeat measurements are possible. ► Exs: Compute std. dev. from repeated absorbance or temperature measurements “Type B” evaluation: u = s/√3 Applicable when upper & lower limits are known (or estimated) but repeat measurements cannot be made. ► Exs: Volumetric glassware tolerances; analytical balance +/– specs

18. Uncertainty Budget & Expanded Uncertainty Include contributions of all aspects u 1, u 2, u 3, etc. to measurement uncertainty Compute combined uncertainty: U c = [u 1 2 + u 2 2 + u 3 2 +... + (etc. ) ] ½ Then obtain expanded uncertainty with coverage factor k: U = kU c

19. Comparison of Uncertainty Estimate to Acceptance Criteria Acceptance Criterion →

20. Example: Method for Organonitrogen Pesticides in Air 01020304050 Carbendazim Thiobencarb Propoxur Diuron Propham Methomyl Oxamyl Formetanate Chlorpropham Captan Methiocarb Aldicarb Carbaryl Carbofuran Methomyl Carbendazim 5% Lower Confidence Limit 95% Upper Confidence Limit Uncertainty (Accuracy) ← 25% acceptance criterion

21. Summary Overview of use of analytical uncertainty, QA/QC & consensus standards Overview of use of analytical uncertainty, QA/QC & consensus standards Criteria for acceptable analytical performance Criteria for acceptable analytical performance Myriad applications & requirements in commercial & government laboratories Myriad applications & requirements in commercial & government laboratories Coverage of statistics in analytical chemistry curricula could be augmented by discussion of these areas Coverage of statistics in analytical chemistry curricula could be augmented by discussion of these areas

22. Questions / Comments? Contact Info : Dr. Kevin Ashley U.S. Department of Health and Human Services Centers for Disease Control and Prevention National Institute for Occupational Safety and Health 4676 Columbia Parkway, Mail Stop R-7 Cincinnati, Ohio 45226-1998 (USA) Tel. +1(513)841-4402; e-mail: KAshley@cdc.gov KAshley@cdc.gov www.cdc.gov/niosh