Pacific Rim Labs offers a specialized PFAS assay called "TOP Assay" ("Total Oxidizable Precursor Assay") for estimating the total levels of PFAS in a sample.

Most labs, including Pacific Rim Labs, will analyze directly for around 30 PFAS analytes in a sample. However, there are over 6000 different PFAS substances in circulation globally. Your sample may have very low levels of PFOA, but may have higher levels of other PFAS that would degrade in the environment to produce PFOA. 


How do you measure PFAS "precursors" in a sample?

You run a TOP Assay.


Pacific Rim Labs offers TOP Assay services and we have participated in two global proficiency studies for this test, helping to verify that our TOP Assay is effective. 

How is a TOP Assay different from a typical analysis?

TOP Assay consists of analyzing your sample twice: 

Analysis of your sample as received (called "pre-oxidation analysis")
Analysis of your sample after we oxidize it (called "post-oxidation analysis")

      👉 The TOP Assay results are the comparison between the pre-oxidation and post-oxidation samples. 

How do you interpret TOP Assay results?

This table is a rough guide on interpreting TOP Assay results:

  • "PFAS PRECURSORS" refer to any of the >6000 PFAS labs do not typically analyze for (yet).
  • "PFAS" refers to any of the 28 PFAS that labs do analyze for.

TOP Assay interpreting results

How is a TOP Assay able to measure >6000 different PFAS at one time?

  • The TOP Assay uses a chemical reaction ("oxidation") to convert the over 6000 possible PFAS in your sample into PFAS on Pacific Rim Lab's 28 PFAS list (this is the "post-oxidation analysis").
  • If the post-oxidation sample contains higher levels of the 28 PFAS compared to the non-oxidized sample ("pre-oxidation"), it is evidence supporting the presence of PFAS precursors.
  • Generally, the higher the level of PFAS in the post-oxidation sample, the higher the levels of background PFAS precursors in your original sample.
  • The TOP Assay does not identify which of the >6000 individual PFAS are present in the sample, but only tells you if there are other PFAS precursors and generally how much extra PFAS there is.