When an environmental project includes analysis of per- and polyfluoroalkyl substances (PFAS), project managers need a clear and accurate picture of their data. Extremely low reporting limits and complex sample matrices leave little room for error when teams make project decisions.
Laboratory reports provide the results, but they do not always show how the laboratory generated those results. Stage 4 data validation gives project teams greater visibility into the analytical process and helps confirm that PFAS data are accurate, reliable and suitable for their intended use.
Why data validation matters
Many environmental program managers and stakeholders view the commercial laboratory as a black box: Samples go in and results come out, with limited visibility into how the laboratory generated the data.
Data users may then make project decisions based on the assumption that every reported value is accurate and comparable over time. However, the analytical method, sample matrix, instrument performance and laboratory practices can all influence the final result.
As commercial laboratories further refine modifications to U.S. Environmental Protection Agency (EPA) Method 537.1 or incorporate U.S. EPA Method 1633 for PFAS extraction and analysis, data users need to understand both the quantitative and qualitative accuracy of the results their laboratories produce.
Independent data validation helps provide that understanding.
Why Stage 4 data validation for PFAS
Stage 4 data validation provides the highest level of scrutiny. It gives project teams greater confidence that PFAS results are defensible, accurate and representative of site conditions.
Onterris references the Stage 4 data validation requirements specified in the National Functional Guidelines and the U.S. Department of Defense Data Validation Guidelines, as applicable to the project.
Stage 4 data validation is a thorough and advanced review process. It goes beyond completing a checklist. Onterris data validation experts apply professional judgment, logic and critical thinking to evaluate the complete analytical record.
A critical part of Stage 4 validation is the review of instrument raw data. Experienced chemists evaluate PFAS-specific requirements and analytical factors that a less detailed review may overlook. This process can identify concerns related to data integrity, reliability and usability before the project team makes a decision.
Best practices: instrument raw data review
Chromatographic information and several sample-specific quality-control metrics are available only in the instrument raw data. These files are generated by the software the laboratory analyst uses to process the analytical results.
The data reviewer evaluates this information to assess both qualitative identification and quantitative accuracy. As a central component of Stage 4 validation, instrument raw data review can determine whether reported results are accurate, reliable and free from significant errors or interferences.
The review addresses several critical questions.
Did the target analyte peak used for quantitation elute from the system within the expected retention-time range?
This evaluation can identify potential false-positive or false-negative results. Onterris has observed that branched isomer peaks can influence retention-time assessments, whether or not the laboratory includes those peaks in the reported result.
A reviewer must therefore consider the full chromatographic pattern, not only the retention time listed in the final report.
Was the target analyte signal strong enough to distinguish it from background or system noise?
This evaluation can identify potential false positives or tentative identifications. Onterris has observed cases where laboratory personnel did not fully understand how the instrument software measured noise.
A numerical signal-to-noise ratio may appear acceptable while a visual review of the chromatogram shows a higher level of background noise. Reviewing both the calculated value and the chromatographic evidence provides a more complete assessment.
Was the confirmation ion present? Was the ratio between the target analyte’s quantitation ion and confirmation ion within the established acceptance criteria?
This evaluation can identify false positives and results that may be estimated or biased. Onterris has observed that laboratories do not always qualify a result when the confirmation ion is absent.
A complete review considers whether the available ion information supports the reported identification and concentration.
Did the laboratory quantify the reported target analyte using a clearly defined peak? Did the sample matrix or another interference affect peak integration? Did the laboratory identify and report the correct linear or branched isomer peaks?
These evaluations can identify false positives, tentative identifications and results that may be estimated or biased.
Together, the four areas of review strengthen confidence in the analytical data. They help confirm that the laboratory results are accurate, reliable and appropriate for project use.
However, rigorous validation is only part of the process. Project teams must also understand how their laboratory quantifies and reports PFAS, particularly when evaluating historical trends.
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Laboratory quantitation can change the story
When evaluating historical trends in linear and branched isomer reporting, project teams need to understand what the laboratory reports and how it calculates the result.
Two Onterris chemists recently identified a change in a client’s commercial laboratory calibration practices. The laboratory had moved from linear-only peak calibration for certain compounds to calibration based on combined linear and branched peaks.
This change produced a meaningful quantitative difference when the team compared the new results with more than a decade of historical data generated using linear-only calibration.
U.S. EPA Method 1633 allows laboratories flexibility as new commercial standards become available. However, that flexibility can change the basis of quantitation over time, even when the method reference listed in the laboratory report remains the same.
A project team reviewing only the reported concentrations could interpret the difference as a change in site conditions. A review of the calibration approach showed that the analytical practice had also changed.
This example demonstrates why laboratories and data users should document changes in calibration, quantitation and reporting practices. Understanding how the laboratory produced the result is essential when comparing data across different sampling events, instruments or time periods.
Bringing greater clarity to PFAS data
Stage 4 data validation helps open the black box of laboratory PFAS analysis. It provides a more complete and accurate picture of the data so project teams can make informed decisions.
As PFAS programs develop and analytical practices continue to evolve, robust validation remains an important part of data quality. A detailed review can identify potential errors, explain apparent inconsistencies and clarify whether the results support the project’s objectives.