Reporting Limits – How Good Are They

1. Reporting Limits – How Good Are They

2. 2010 ASQ Workshop September 20th to September 25th ,2010 Seattle, WA Robert P. Di Rienzo Quality Assurance Manager ALS Laboratory Group Salt Lake City, UT Ft. Collins, CO

3. Definitions and Requirements • How is the Data Generated • Are you Ready to Rumble…….. (Data) • Other uses for Reporting Limit Data • Conclusions

4. Definitions and Requirements Limit of Detection (LOD): an estimate of the minimum amount of a substance that an analytical process can reliably detect. An LOD is analyte- and matrix-specific and may be laboratory dependent. The LOD is equivalent to the MDL. The protocol for determining LODs shall be documented. All sample processing steps of the analytical method shall be included in the determination of the LOD.

5. Definitions and Requirements Limit of Quantification (LOQ): the minimum levels, concentrations, or quantities of a target variable (e.g., target analyte) that can be reported with a specified degree of confidence. The LOQ is equivalent to the Practical Quantitation Limit (PQL). For analyte calibration curves of more than two points, the lowest point above LOD determines the LOQ. The LOQ shall be no less than three times the LOD.

6. Definitions and Requirements Precision: The degree to which a set of observations or measurements of the same property, obtained under similar conditions, conform to themselves; a data quality indicator. Precision is usually expressed as standard deviation, variance or range, in either absolute or relative terms. Bias: The systematic or persistent distortion of a measurement process, which causes errors in one direction (i.e., the expected sample measurement is different from the sample’s true value). Accuracy: The degree of agreement between an observed value and an accepted reference value. Accuracy includes a combination of random error (precision) and systematic error (bias) components that are due to sampling and analytical operations; a data quality indicator.

7. Definitions and Requirements Coefficient of variation: The coefficient of variation (CV or Sr) is a normalized measure of dispersion or a probability distribution. It is defined as the ratio of standard deviation to the mean.

8. Definitions and Requirements • Uncertainty: • a term used in subtly different ways in a number of fields, including philosophy, physics, statistics, economics, finance, insurance, psychology, sociology, engineering, and information science. It applies to predictions of future events, to physical measurements already made, or to the unknown. • 2) If outcomes will occur with a probability that cannot even be estimated, the decision-maker faces uncertainty.

9. Definitions and Requirements Uncertainty: 3)

10. Definitions and Requirements Calculating Uncertainty: The Sr value may be used to calculate uncertainty at the LOQ . The calculation takes into consideration precision and bias and calculates uncertainty at the 95% confidence level. ± 2(Sr)

11. Definitions and Requirements Reporting Limit Verification Sample Reporting Limit Verification Sample (RLVS or RVS) is a quality system matrix spiked sample prepared to have a concentration at the LOQ and taken through the entire preparation and analytical process.

12. How is Data Generated Reporting Limit Verification Sample Analyzed in each batch of samples. RLVS/RVS is a spiked LCS sample at or below the LOQ. These samples are used to assess precision and bias at the LOQ. This data are used to calculate uncertainty and/or control limits at the reporting limit and may be used as a data quality indicators on a project specific basis.

13. Are you Ready for Data? >20,000 Data Points in 2009 & 2010

14. Example Method Data Just Kidding

15. Example Method Data Uncertainty calculated using historical data for RLVS/RVS and LCS at 95% confidence interval

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31. Other Uses for Reporting Limit Data • Assessment of Laboratory LOQ • Calculation of Statistically Valid Detection Limits

32. Assessment of Laboratory LOQ

33. Calculation of Statistically Valid Detection Limits Traditional Detection Limit Calculations are Statistically Challenged • Does not assess variability over time. • Does not correct for method bias (Method Blanks). • Does not correct for recovery. • Uses estimated data to calculate 99% confidence. • Uses normal statistics for non normal data.

34. Calculation of Statistically Valid Detection Limits Detection Limit Calculation using RLVS DL(MDL) = Bo + Sr (LOQ / (µR)) LOQ = The spiked concentration of RLVS Sr = Coefficient of Variation from RLVS measurements Bo = Average Blank Value (MB, or CCB) or 0 (Optional) µR = Mean Recovery of RLVS Samples (Optional)

35. Conclusions • RLVS on a batch basis will generate data for uncertainty at the reporting limit. • An assessment of the LOQ can be made from the coefficient of variation (Sr) • Precision and bias at the LOQ is significantly different than at the LCS level.

36. Conclusions

37. Questions? Robert P. Di Rienzo Quality Assurance Manager ALS Laboratory Group (Salt Lake City, UT) (Ft. Collins, CO) Bob.DiRienzo@ALSGlobal.com (801) 266-7700