Deep Eutectic Solvent Stir Bar Sorptive Extraction: A Rapid Microextraction Technique for the Determination of Vitamin D(3) by Spectrophotometry

[Image: see text] In this paper, a new microextraction method, named deep eutectic solvent stir bar sorptive extraction (DES–SBSE), is described that utilizes a hydrophobic DES (hDES) as a coating for SBSE. As a model, vitamin D(3) was extracted efficiently by this technique from different real samples before its spectrophotometric determination. A conventional magnet was encapsulated inside a glass bar (1.0 cm × 2 mm) and coated by the hDES consisting of tetrabutylammonium chloride and heptadecanoic acid (mole ratio 1:2). Parameters affecting microextraction were studied and optimized by one-variable-at-a-time, central composite design, and Box–Behnken design methods. Under the optimum conditions, the detection limit of 0.08 μg L(–1) could be reached. The linear range of the method was between 0.5 and 1000.0 μg L(–1) for the analyte. Precision for intraday repeatability and interday reproducibility of the method was better than 3.1 and 4.2, respectively. A single stir bar could be used for at least 50 successive extractions and the batch-to-batch reproducibility of SB coated with hDES was 4.5%.