LC-MS/MS software can calculate a PFAS concentration within seconds. That number does not become a defensible result until the laboratory reviews the chromatography, calibration, quality controls, and sample history.
Data review should trace each reported value from the chromatogram to the final unit. The reviewer must determine whether the peak represents the target analyte, whether the method quantified it within a controlled range and whether any failure limits its use.
Begin With the Sample Record
Review starts before the chromatogram. The reviewer should confirm that the laboratory used the requested method and that the sample met requirements for container, preservation, holding time, and preparation.
Dilutions, subsampling, re-extractions, and deviations can change the reporting limit or interpretation. These actions must remain connected to the final result.
The EPA Method 1633A uses several criteria to establish identity, including signal-to-noise ratio, retention time, and ion ratio where a reliable confirmation transition exists.
The reviewer should examine:
- Retention time against the calibration standard
- Coelution with the labelled analogue
- Quantifier and qualifier transitions
- Ion ratio, where applicable
- Linear and branched isomer pattern
- Peak shape and baseline
- Potential interference
- Integration boundaries
These checks should use the raw chromatogram rather than a concentration table alone.
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Some PFAS lack a dependable confirmation ion. In these cases, retention time, labelled-standard behavior, and clean background carry greater weight.
Review Integration Consistently
Automated integration can fail when peaks sit near the reporting limit, overlap with background, or show unusual shapes. Manual integration may correct the result, but it also introduces analyst judgement.
The laboratory should define when manual integration is permitted and how reviewers document it. Analysts should apply the same approach to samples, standards, and quality controls.
A reviewer should question integrations that exclude part of an isomer pattern, shift the baseline to create a detection, or treat similar peaks differently across the batch.
Check the Quantitative Range
Results must fall within the established calibration range. A response above the highest standard requires an appropriate dilution or another action permitted by the method. A signal below the laboratory’s reporting threshold may require qualification or reporting as a non-detect, depending on the method and project.
Dilution changes more than the calculated concentration. It raises the effective reporting limit and may alter labelled-standard response. The reviewer should verify the dilution factor, final units, and method requirements before accepting the result.
Connect Results With Quality Control
The reviewer should assess each result against the controls that support it. A method-blank detection may affect low-level sample results. A failed labelled-standard recovery may affect only the target compounds associated with that standard. A failed calibration verification can affect samples analyzed since the previous passing check.
Matrix spikes and duplicates provide added context but do not automatically invalidate every result when they fail. The reviewer must determine whether the failure reflects general method performance, a sample-specific matrix effect, or sample heterogeneity.
This analyte-and-sample-level review avoids rejecting unaffected data or releasing results unsupported by the controls.
Assign Qualifiers With a Defined Meaning
A qualifier should tell the data user what limitation occurred. It should not serve as a generic warning attached to any unusual result.
Laboratories should define qualifiers in the report and apply them according to the method, project plan, or regulatory program. Common uses include identifying estimated concentrations, blank-associated results, reporting-limit exceedances, and results that failed an identification or recovery criterion.
A qualified value remains a result with a stated limitation. A rejected value lacks sufficient support for its intended use. The laboratory should not use qualification to rescue data when the governing method requires reanalysis or rejection.
Verify Units and Calculations
PFAS results may be reported in ng/L for aqueous samples and ng/g for solids or tissue. Method 1633A reports soil, sediment, and biosolids on a dry-weight basis, while tissue results use wet weight unless project requirements specify otherwise.
The reviewer should verify sample mass or volume, final extract volume, dilution factors, percent solids, and unit conversions. These checks prevent a sound instrumental result from becoming an incorrect reported concentration.
Write a Useful Case Narrative
The final report should include enough context for the client or regulator to understand departures from normal performance. The case narrative should identify affected samples and analytes, describe the issue, record corrective action, and explain any remaining qualification.
It should distinguish between a laboratory problem and a sample-specific limitation. A failed matrix spike, for example, may show that the sample affected recovery even though the clean control passed.
The goal of review is not to make every result appear acceptable. It is to communicate what the laboratory measured, how well the method supported it, and which limitations the data user must consider.
This article was produced under Separation Science's AI Editorial Guidelines.
