A lab can report "non-detect" on a sample that still contains nanoplastics — because most methods were never designed to see them.
Nanoplastics — generally, particles below 1 µm [1] — sit below the practical resolution of both optical identification methods. Raman's finest routine resolution is around 1 µm [2]; anything smaller simply doesn't produce a strong enough signal to identify reliably.
This creates a specific, avoidable failure mode for any certification scheme built on optical methods alone: a product can pass every particle-count test and still contain a meaningful nanoplastic fraction, because nothing in the test was capable of seeing it. "Non-detect" and "absent" are not the same claim, and conflating them is exactly the kind of overstatement a defensible standard has to rule out.
This is the concrete reason the MPFREE Standard requires Py-GC-MS as part of its top certification tier rather than treating it as optional: because it measures total polymer mass rather than counting particles, it captures the nanoplastic fraction the two optical methods structurally cannot [3]. A product tested only by µFTIR and Raman has not been evaluated for nanoplastics at all — it has been evaluated for everything above roughly 1 µm.