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 D3was 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–1could be reached. The linear range of the method
was between 0.5 and 1000.0 μg L–1for 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%.