The HS nomenclature separates the free acid (290431) from its ammonium salt (290432) because they are distinct chemical entities with different physical properties, CAS numbers, and potentially different regulatory treatment. In practice, both are subject to stringent PFAS controls, but the legal instruments — EPA SNURs, Stockholm Convention exemptions — may apply differently to the acid versus the salt, making precise identification of the chemical form essential for both classification and regulatory compliance.

At minimum, importers should present a certificate of analysis confirming the chemical identity (including CAS number), a commercial invoice specifying the intended end use, and evidence of EPA TSCA compliance — such as confirmation that the use is covered by an existing SNUR exemption or that a SNUN has been filed and cleared. Given CBP's increasing focus on PFAS imports, having this documentation organized before arrival at the port of entry reduces the risk of a hold or examination.