Proficiency Testing Process

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Proficiency Testing Process

• Analytical Products Group, Inc.
• Tom Coyner

2
Steps in PT Production Verification Process

• Sample Design
• Production
• Verification Homogeneity
• Distribution
• Data Analysis
• Stability Testing
• Reporting

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Sample Design

• PT samples should be designed to challenge the
  analytical system.
• Test the critical step in any analytical method

4
Production

• Raw Material selection
• Raw Material identity and assay verification
  testing.
• Testing includes water, solvents, and contaminates

5
Verification Homogeneity

• Is the Assigned Value Correct?
• Testing is done versus NIST SRMs where available
  or 3rd party standards
• A PT providers testing must be three times
  better than that expected from the laboratories.

6
Verification Homogeneity

• Do all samples shipped to the laboratories have
  the same Assigned Value?
• Compare the variability between samples to the
  variability within samples.
• ANOVA analysis F Test

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Distribution

• PT Testing is a peer review process
• All laboratories must be treated fairly and
  equally.
• Same day shipment
• Same closing date
• No exceptions!

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Data Analysis

• For WS/WP analytes covered by USEPA or the NELAC
  program most analytes are evaluated on the
  Assigned Value NOT on the actual data submitted
  by the laboratories.
• This is not a peer review process

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Data Analysis

• Regression Constants are used for many analytes.
  Fixed limits are used for some WS analytes.
• Mean (Assigned Valuea) b
• Std Dev (Assigned Valuec) d

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Data Analysis

• Acceptance Limits are set as
• WP Mean 3 Std Dev
• WS Mean 2 Std Dev
• Assigned Value
• All providers use the same limits.

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Data Analysis

• The handling of less than values is determine by
  either the USEPA Criteria Document or NELAC Board
  Policy.

12
Stability Testing

• Is the Assigned Value at the end of the study the
  same as it was at the beginning of the study?
• Can be determined by comparing results before
  shipment with results after the close date.
• Comparison using a t Test on Means.

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Reporting

• The reporting requirements of USEPA and NELAC
  include only
• Analyte
• Assigned Value
• Laboratory Result
• Acceptance Limits
• Evaluation
• Anything else you can get is a bonus to the
  laboratory!

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Reporting

• If sufficient information is reported to the
  laboratory then a PT program can be used by the
  laboratory for quality improvement rather than
  being simply used by the state for laboratory
  monitoring and enforcement.
• The international harmonized protocol recognizes
  the use of proficiency testing for quality
  improvement.

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Analytical Products Group, Inc.

• A partnership in compliance