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Method Modifications. Mentoring Session Technical Assistance Committee. TNI Training Disclaimer.

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Method Modifications

Mentoring Session

Technical Assistance Committee

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TNI Training Disclaimer

  • The material presented in this session is for informational purposes only. It is designed to promote understanding, consistency and clarification of technical and accreditation requirements. It should not be considered a change or alteration of the Accreditation standards, the published methods, a regulatory agency requirement or a position of TNI.

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Method Modifications

The primary objective of method

modifications is to enhance precision and

accuracy for each analysis.

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All laboratories large and small:

Such as commercial and private (including municipalities) must prove that their method modification to any approved standard analytical method is valid.

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What to Document

The information and supporting data, required during the validation, must be sufficient to allow an independent reviewer (EPA, state or contractor) to verify each determination and calculation performed by the laboratory.

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  • Where more than one matrix type is involved (e.g., air, soil, water, sludge)

    • The laboratory must validate the method on each matrix type.

  • In most cases several different samples should be involved in the validation,

    • Example: Non-Potable Water several effluent samples from different plants should be used.

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    Method Modifications

    • Validation Criteria:

    • Must include the documented procedure used to validate and report the data

    • Should explain the statistical analysis of study results.

    • Must include all raw data results to allow for a complete independent reviewer verification

    • Should be checked by comparing the performance criteria with the actual approved standard method, as written.

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    Quality Control

    • What is involved?

    • Initial Precision and Recovery

      • Calibration (initial and continuing)

      • Method Detection Limit (MDL),

      • Laboratory fortified blank

      • Matrix Spikes

      • Method Blanks

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    Quality Control

    • Internal standard/s

    • Surrogate standard/s

    • Tracer (for radiochemistry)

    • Control charts or other trend analyses

    • Quality Control acceptance criteria

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    Raw Data

    • Sample numbers or other identifiers used

    • Sample preparation (extraction/digestion) dates

    • Analysis dates and times

    • Sequence of analyses or run logs

    • Sample volume

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    Raw Data

    • Extract volume prior to each cleanup step

    • Extract volume after each cleanup step

    • Final extract volume prior to injection

    • Digestion volume

    • Titration volume

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    Raw Data

    • Percent solids or percent moisture

    • Dilution data - differentiating between dilution of a sample and dilution of an extract

  • Instrument(s) and operating conditions, such as:

  • GC and/or GC/MS: including detailed information on columns used for determination and confirmation (column length and diameter, stationary phase, solid support, film thickness, etc.) In addition, analysis conditions (temperature programs, flow rates, etc.) must be documented

  • Detectors: type, operating conditions, etc.

  • Chromatograms: ion current profiles, bar graph spectra, library search results , etc

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    Raw Data

    • Data Quantitation reports, system outputs, and other data to link the raw data to the results reported. (Where these data are edited manually, explanations of all manual changes must be included)

    • Direct instrument readouts; strip charts, printer tapes, etc., and other data to support the final results

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    Raw Data

    • Laboratory bench sheets and copies of all pertinent logbook pages for all: sample preparation, cleanup, and determinative steps of the analysis

    • Dilution data - differentiating between dilution of a sample and dilution of an extract

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    Example: 1

    When using 1000 mL sample, the pipet used in the method is a 25 mL wide bore, this would take an analyst 40 separate measurements to deliver the volme

    Standard Methods 2540 D.

    Total Suspended Solids

    Sample Analysis:

    3 (b) states to stir the sample and pipet an aliquot from the midpoint of the container

    Modification: Using a graduated cylinder (1000 ml) instead of the 25mL pipet, reduces analyst time and handling of the sample

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    Example: 2

    • The use of an alternate QA/QC chemical in place of the Glucose/Glutamic Acid (GGA) for BOD/CBOD.

    • Laboratories that are using KHP (Potassium Hydrogen Phthalate) for their BOD/CBOD depletion chemical.

    • Does the laboratory have the right to modify the method to a degree of changing the chemistry?

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    • 40 CFR 136.6 Method modifications and analytical requirements.

    • Flexibility to Modify CWA Method Nov 20, 2007

    • EPA: Solutions to Analytical Chemistry Problems with Clean Water Act Methods 2007 (Pumpkin Book)

    • (EPA 821-B-98-002 EPA Approval of Alternate Test Procedures for Organic and Inorganic Analytes in Wastewater and Drinking Water March 1999)