When an environmental project includes the analysis of per- and polyfluoroalkyl substances (PFAS), it is imperative that environmental project managers have a clear and accurate picture of their data. With extremely low reporting limits and various potential matrix issues, there is no room for error when making project decisions.
The Importance of Data Validation
Many environmental program project managers and other stakeholders consider their commercial laboratory a black box, where samples go, and results come out, with little consideration given to how the results were generated. Those data users then make decisions for their environmental project based on the assumption that every reported value is accurate and comparable over time.
As commercial laboratories further refine modifications to US EPA Method 537.1, or incorporate US EPA Method 1633 for the extraction and analysis PFAS, it is imperative that end users fully understand the data being generated by their laboratory for both quantitative, and qualitative accuracy.
Why Stage 4 Data Validation for PFAS?
Stage 4 data validation provides the highest level of scrutiny, delivering confidence that your PFAS results are defensible, accurate, and truly representative of your site conditions.
Environmental Standards routinely references Stage 4 data validation requirements specified in National Functional Guidelines, as well as U.S. Department of Defense (DOD) Data Validation Guidelines to ensure compliance.
Stage 4 data validation is a very thorough and advanced approach to the validation process. It is so much more than a checklist. Our data validation experts use professional judgment, logic, and critical thinking skills as no stone is left unturned. Associate Chemist Ammie Martin recently authored an article detailing the extensive steps Environmental Standards takes when performing Stage 4 data validation, steps that go above and beyond the status quo to ensure high-quality, defensible data.
A critical component of Stage 4 data validation is a meticulous review of instrument raw data. PFAS-specific requirements and factors, which can be overlooked during a less thorough review, are carefully evaluated by experienced chemists to identify any issues related to data integrity and reliability.
Best Practices for Effective Validation: Instrument Raw Data Review
Chromatographic review and several sample-specific quality control (QC) metrics are only available in the instrument raw data, which are outputs from the data processing software used by the laboratory analyst in processing the data. The data reviewer evaluates this unprocessed data to assess the qualitative and quantitative results. As a central component of Stage 4 data validation, instrument raw data review can identify whether reported results are accurate, reliable, and free from errors or interferences. This review can address critical questions, such as:
Retention time/expected retention time: did the target analyte peak(s) used to quantitate elute from the system and the expected retention time?
False positives or false negatives could be determined from this evaluation. Environmental Standards has observed that the presence of branched isomer peaks can influence the retention time evaluation, whether or not they are to be included in the result
Signal-to-noise (S/N) ratio: was the target analyte peak signal strong enough to differentiate from background/system noise?
False positives/tentative identifications could be determined from this evaluation. Environmental Standards has observed that laboratories often do not know how the instrument measures noise, and a visual examination of the chromatogram may exhibit a higher background noise level than revealed by the numerical S/N ratio.
Confirmation ion and ion transition ratio: was the confirmation ion present and was the target analyte’s ratio between the quantitation (primary) ion and confirmation (secondary) ion within the expected/established ratio criterion?
False positives or estimated/biased results can be detected through this evaluation. Environmental Standards has observed that laboratories frequently do not qualify the result if the confirmation ion is not present.
Chromatographic review: were reported target analytes quantitated from clearly defined peaks? Did sample matrix/interference hinder peak integrations? Were proper linear/branched isomer peaks reported?
False positives, estimated/biased results, and/or tentative identifications could be determined from these evaluations.
Together, these evaluations strengthen confidence in the data and ensure that results issued from the laboratory are both accurate and defensible. However, even with rigorous data validation, understanding how your laboratory is quantitating and reporting results remains essential, especially when evaluating historical trends.
Laboratory Quantitation: The Devil’s in the Details
For evaluating historical trends in linear and branched isomer reporting, understanding what is being reported and how it is being quantitated by your laboratory is crucial. Recently, two Environmental Standards chemists determined their client’s commercial laboratory had made a change in instrument calibration practices; switching from some linear-only peak calibrations to combined linear and branched peak calibrations. This resulted in a meaningful quantitative difference when compared to over a decade’s worth of historical data that had been quantitated using the linear-only calibrations.
US EPA Method 1633 allows laboratories this flexibility as new commercially available standards are applied, but this flexibility means that the quantitation changes over time, even though the method reference does not. This illustrates why understanding what your laboratory is reporting is necessary for trend evaluation.
Environmental Standards: Here to Help
Unlocking the black box of laboratory PFAS analysis through Stage 4 Data Validation is the key to having a thorough and accurate picture of your data. When you have that information, you can make better decisions for your environmental program. As awareness of PFAS contamination grows, the importance of robust validation processes becomes increasingly clear.
With a deep bench of experienced chemists, Environmental Standards is ready to assist with your PFAS Stage 4 Data Validation needs. We’ll help you see inside the “black box” and give you confidence in the quality and reliability of the data that drive your projects. Contact us for a free consultation today!
