Mixed Analyte Performance Evaluation Program

1. Mixed Analyte Performance Evaluation Program INORGANIC TOPICS: FALSE POSTIVE TESTING REPORTING UNCERTAINTIES MAPEP TEAM Radiological & Environmental Sciences Laboratory Mary C. Verwolf

2. Inorganic False Positive Testing • Uncertainties not typically reported for inorganic analytes • Forces Separate Criteria for Evaluating False Positive Testing for Inorganic Results • Evaluation Based on the Lower Limit of the Concentration Range

3. Inorganic False Positive Testing STABLE INORGANIC CONSTITUENT DESCRIPTION LCDL = Lower Concentration Detection Limit for Inorganic Analyte • Detection Limit is the Lower Concentration Range in Sample Description • LCDL is based on EPA’s CLP Contract Required Detection Limits

4. Evaluating Inorganic False Positive Test Result Reported DL= LCDL: Acceptable Result LCDL Flag <0.01 <0.01 A Result Reported DL< LCDL: Acceptable Result LCDL Flag <0.005 <0.01 A Result Reported DL> than LCDL: Acceptable Result LCDL Flag Note <0.02 <0.01 A (7) Reported DL > LCDL Result Reported Value > LCDL: Not Acceptable Result LCDL Flag Note 0.0115 <0.01 A (N) False Postive

5. Inorganic False Positive Testing Examples of Inorganic False Positive Test

6. Reporting Inorganic Result with Uncertainty • An analytical result is not an absolute value • Uncertainty defines the range that true value is expected to lie within Result +/- Uncertainty For Over 17 years MAPEP has encouraged reporting uncertainties with all results!

7. International Emphasis on Reporting Data with Uncertainty • International Labs report results with uncertainties • International Standards Require Results with uncertainties • ISO 17025 requires analytical results with uncertainty • NIST recommends reporting a result with an uncertainty MAPEP is again considering making the reporting of a result with uncertainty mandatory for inorganic results!

8. Excuses for Not Reporting Result with Uncertainty • “It’s to complicated!” • “We need a statistician on staff!” • “That’s only required for Rad results!” • “EPA doesn’t require results with uncertainties.” You can do it – Simple Example for Propagating Uncertainty for the Determination of Arsenic in Water.

9. Propagating Uncertainty of Inorganic Analysis Result Propagate a total combined uncertainty by statistical rules and the combination of variances: Estimate all uncertainty components, as approximations to standard deviations Type A, sA - derived from a statistical analysis Type B, sB- evaluated by other means

10. Propagating Uncertainty of Inorganic Analysis Result Simple Example: R= Result U1= uncertainty component of sample weight, U2= uncertainty component of volumetric flask U3=uncertainty component of instrument reading, etc.

11. Propagating Uncertainty for the Analysis of Arsenic in Water Simple Example for Estimating Uncertainty 1) Identify uncertainty contribution for each analytical step 2) Evaluate the uncertainty for each contribution

12. Propagating Uncertainty for the Analysis of Arsenic in Water • Uncertainty from replicate measurements of a Calibration Standard or Laboratory Control Standard • Standard Deviation for a single operator over different days • Standard Deviation for various operators over different days • Instrument Measurement Uncertainty from Calibration Curve • Estimated error from Calibration Curve

13. Calibration Curve Error

14. Combined Uncertainty of Inorganic Analysis Result Combined uncertainty = Result * sum of squares in quadrature Report Result with the Combined Uncertainty 21.5 +/- 0.3 mg/L Single Operator Single Day

15. Future MAPEP Inorganic False Positive & Sensitivity Testing Uncertainty is as important as the result MAPEP will use the result with uncertainty for evaluating False Postive and Sensitivity Testing in the Future for Inorganic Results

16. References • NIST Technical Note 1297, 1994 • ISO/IEC/OIML/BIPM Guide to the Expression of Uncertainty in Measurement: 2008 • NCSL Information Manual, Determining and Reporting Measurement Uncertainties, RP-12, 1994 • ANSI N42.14-1991; NCRP Report No. 58, second edition, 1985).