A Sustainable Vortex-Assisted NADES-LLME Approach Employing Thymol–Lactic Acid for the Efficient Extraction and Determination of Patent Blue V in Oral Pharmaceutical Formulations

A vortex-assisted liquid–liquid microextraction (VA-LLME) method employing a thymol–lactic acid natural deep eutectic solvent (TL-NADES, 1:2 molar ratio) was developed and validated for the sensitive determination of Patent Blue V (PBV). Experimental variables affecting extraction, including solution pH, NADES volume, vortex duration, centrifugation time, and sample volume, were systematically optimized using a one-factor-at-a-time strategy. Under the optimized conditions pH 6.0, 250 µL NADES, 30 mL sample volume, vortexing for 2 min, and centrifugation at 4100 rpm for 2 min, the method provided efficient phase separation and quantitative extraction. Analytical validation demonstrated excellent performance, with a limit of detection (LOD) of 7.1 ng mL−1, a limit of quantification (LOQ) of 23.8 ng mL−1, and linearity in the range of 23.8–100 ng mL−1 (R2 = 0.9897). Precision was confirmed with relative standard deviation (RSD%) values consistently below 5%, while preconcentration and enhancement factors were 60 and 50, respectively. The method achieved an extraction efficiency of 83%. Application to real pharmaceutical formulations (oral spray, mouthwash, and antibiotic mouthwash) revealed background PBV levels of 0.71–1.52 µg g−1, with recovery studies yielding satisfactory values between 93% and 105%. The proposed TL-NADES-LLME approach offers a simple, rapid, and environmentally sustainable alternative to conventional extraction techniques, with demonstrated applicability for trace-level monitoring of PBV in complex pharmaceutical matrices. Its high sensitivity, robustness, and green profile emphasize its potential for broader use in pharmaceutical quality control and food safety monitoring.