Green Liquid-Phase Microextraction Using Nonanoic Acid as a Novel Extractant for the Spectrophotometric Determination of Rhodamine B in Cosmetics

A new method for separating and concentrating Rhodamine B (RhB) in cosmetics has been developed using nonanoic acid liquid-phase microextraction (NA-LPmE) with spectrophotometric determination. Nonanoic acid is a novel and environmentally friendly extractant that was used as a single component in the isolation. In contrast, supramolecular solvents and deep eutectic solvents are often combined as a mixture. The method is simple, quick, accurate, and environmentally friendly. The appropriate parameters (the volume of NA, pH, sample volume, and matrix effects) were optimized and these conditions resulted in a suitable linear range (20.5–1000 µg L−1), low detection limit (6.2 µg L−1), and high pre-concentration factor (40). The NA-LPmE method successfully extracted and determined RhB in several cosmetics and employs a small volume of green solvent with spectrophotometric determination and rapid analysis. The combination of nonanoic acid and RhB was used for the first time.