9902.05.28 - Butyl methylphosphinate (CAS No. 6172-80-1) (provided for in subheading 2931.39.00).

This HTS category, 9902.05.28, specifically classifies Butyl methylphosphinate (CAS No. 6172-80-1). This chemical compound falls under Chapter 99, which is reserved for temporary legislation, modifications to trade agreements, and specific import restrictions. The inclusion of the CAS number is critical for precise identification, differentiating it from other phosphinates or related chemical substances that might be classified elsewhere in the HTS.

As this is a leaf node within the HTS database, there are no subcategories. Therefore, the primary focus for classification purposes is to ensure that the imported good precisely matches the chemical name and CAS number provided. Any ambiguity or the presence of other substances would necessitate a review of the foundational classification for Butyl methylphosphinate, which is provided for under subheading 2931.39.00, indicating its original placement within the broader category of organo-inorganic compounds.

The context within Section XXII signifies that this classification is subject to special provisions and potential temporary restrictions. This means that while the chemical identity is fixed, its import status might be governed by specific, time-limited regulations, distinguishing it from permanent classifications found in earlier chapters of the HTS. Importers must be aware of these temporary modifications and any associated documentation requirements that may apply.