Achieving Success When Analyzing PT Standards

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Achieving Success When Analyzing PT Standards

• Chuck Wibby
• President

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Hardcopy of presentation
www.wibby.com info_at_wibby.com 303-940-0033
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Presentation Overview

• Why are PTs Different
• The Fundamental Problem with PTs
• The Administrative Process
• The Analytical Process
• The Reporting Process
• Recent Developments

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• Why PTs
• Are
• Different

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PTs and real samples

• PTs actually contain analytes (lots of them)
• Come in ampules and require dilution
• DQOs are different (from method and customer
  requirements)
• Very important (actual and perceived value)

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• The
• Fundamental
• Problem

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The Fundamental Problem

• Labs and State Accrediting Authorities have
  different goals for the PT Program.

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The States Goals

• Use PT results to determine whether or not a
  laboratory is competent to analyze samples and
  report results.

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The Labs Goal

• Pass the PTs
• and
• Maintain Accreditation.

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The Attestation Statement

• Labs must sign off on an attestation that they
  analyzed their PT standards just like any other
  routine sample.

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What does this mean?
Calibrate..ICV/ICBLCSSamples...CCV/CCB.LCS
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PT Analysis
Calibrate..ICV/ICBLCSSamplesPTsSamples..CCV/CC
B.LCS
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PT Specific QC
Calibrate..ICV/ICBLCSSamples..PTs...CCV/CCB.
PT Specific QC
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Average of Multiple Analyses
Calibrate..ICV/ICBLCSPTs...CCV/CCB.LCS
PTs...
PTs...
PTs...
PTs...
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PT Specific LCS
Calibrate..ICV/ICBLCSSamplesPTs...CCV/CCB
PT Specific QC
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The PT Process
The Administrative Process
The Analytical Process
The Reporting Process
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• The
• Administrative
• Process

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The Administrative Process

• Knowing when the PTs will arrive
• Receiving and Unpacking
• Logging in
• Distribution
• Communication with staff
• Records

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Receiving and Unpacking

• Instructions
• Data Reporting Sheets
• Samples

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Communication

• Take time to review PT requirements with staff
• Due Date
• Required dilutions
• Record keeping
• DQOs

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• The
• Analytical
• Process

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The Analytical Process

• Opening the PT containers
• Diluting the PTs
• What you should use
• Class A glassware
• Gas tight syringes
• Recording the important information
• Storing the PTs
• Prep and analysis

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Diluting the Standards

• Dont take anything for granted
• Class A glass ware
• Gas tight syringes
• Observe
• Record
• Weight as double check

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Prep and Analysis

• Avoid Unnecessary Prep
• Metals are dissolved
• Clean ups generally not needed
• Dont wait until last day to analyze

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• The
• Reporting
• Process

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The Data Reporting Process

• Results in the diluted sample
• µg versus mg
• Mixed units within one standard
• Transcribing
• Data reporting forms
• Submitting results
• Electronic
• FAX

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The Single Biggest Source of Error

• Transcription errors
• Double check against concentration ranges
• Eliminates most order of magnitude errors
• Does it make sense?
• Results for diluted standard

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Submitting Results

• FAX
• Electronically
• Confirmation of receipt by PT Provider
• Keep copies

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• Recent
• Developments

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Recent Developments

• ELAP publishing concentration ranges and
  acceptance criteria
• Proficiency Testing Reporting Limits (PTRLs)
• PT DQOs

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• PTRLs

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PTRLs
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PTRL Footnote

• NELAC Proficiency Testing Reporting Limits
  (PTRLs) are provided as guidance to laboratories
  analyzing NELAC PT samples. At a minimum, the
  laboratory should use a method that is sensitive
  enough to generate quantitative results at the
  PTRLs shown. NELAC PTRLs are also provided as
  guidance to PT Providers. At a minimum for all
  analytes with an assigned value equal to "0", the
  PT Provider should verify that the PT sample does
  not contain the analyte at a concentration
  greater than or equal to the PTRL.

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How PTRLs Were Derived

• Calculate lowest possible acceptance limit
• Estimate at 50 of lowest possible concentration
• Some reality review

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How to use PTRLs

• For analytes with an assigned value gt0
• Selection of method
• Reality check on result
• For analytes with the possibility of an assigned
  value 0 (VOAs, Semis, Pests)
• Guide to reporting low level positive results

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• PT DQOs

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Regression equations
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Regression equations

• Y mx b
• a, b, c, d????
• Predicted mean (Lab Result a) b
• Predicted SD (Lab Result c) d
• WS Acceptance Limits Pred mean 2 Pred SD
• WP Acceptance Limits Pred mean 3 Pred SD

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Thank You!

• Chuck Wibby
• 303-940-0033
• cwibby_at_wibby.com