Mention the chief use of quaternary ammonium salts derived from long chain amines.

Explanation

**Step-by-Step Solution:**

1. **Definition of Quaternary Ammonium Salts:**
Quaternary ammonium salts are a class of compounds that consist of a nitrogen atom bonded to four organic groups. In this context, they are derived from long-chain amines, which typically have alkyl chains ranging from C8 to C18.

2. **Structure of Quaternary Ammonium Salts:**
The general structure of a quaternary ammonium salt can be represented as R4N^+X^-, where R represents the long-chain alkyl groups and X is the anion (like Cl^-). For example, a common quaternary ammonium salt can be represented as CH3(CH2)15N+(CH3)3Cl^-, indicating a long alkyl chain attached to the nitrogen.

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