2904.31.00.00 - Perfluorooctane sulfonic acid

This HTS category, 2904.31.00.00, specifically covers perfluorooctane sulfonic acid (PFOS). PFOS is a synthetic organofluorine compound that belongs to the class of per- and polyfluoroalkyl substances (PFAS). It is characterized by a sulfonic acid functional group and an eight-carbon perfluorinated alkyl chain. This entry is for the free acid form itself, as distinct from its salt or derivative forms.

It is crucial to differentiate this category from its sibling entries. While all fall under the broader heading of perfluorooctane sulfonic acid and its derivatives, 2904.31.00.00 is strictly for the parent acid. Sibling categories like 2904.32.00.00 (ammonium salt), 2904.33.00.00 (lithium salt), 2904.34.00.00 (potassium salt), and 2904.35.00.00 (other salts) classify the corresponding ionic compounds formed with PFOS. Similarly, 2904.36.00.00 is for perfluorooctane sulfonyl fluoride, a related but chemically distinct compound used as a precursor.

As a leaf node, this classification has no further subdivisions. Therefore, accurate classification relies on confirming the chemical identity of the imported substance. If the material is identified as perfluorooctane sulfonic acid in its non-salt form, it should be classified under this specific code. Any impurities or mixtures should be evaluated according to the general rules of interpretation for the Harmonized System to ensure correct classification.