New challenges in sample preparation: Miniaturized stir bar sorptive dispersive microextraction as a high-throughput...

The miniaturization of stir bar sorptive dispersive microextraction (mSBSDME) for the analysis of low-availability samples is presented. This new methodology is based on the principles of stir bar sorptive dispersive microextraction, but the amount of sorbent and, most importantly, the amount of sample are considerably reduced to a tiny amount and a few microliters, respectively. Thus, affordable 400-μL flat-base glass inserts and minute bar-shape neodymium magnets (3 mm length x 2 mm diameter) were used as extraction devices hold by a specifically designed multiextraction assembly, which comprises a high-rate stirring plate and a 3D-printed support to treat 15 samples simultaneously. This new approach allows a fast, affordable, portable, and high-throughput analysis of low-volume samples, expanding the potential of the technique. The same extraction device is used along the different stages, thus avoiding transfers, which reduces sample handling. Besides, the reduction in the sample, sorbent and organic solvent amounts allows a considerable decrease of the waste generation, and thus pursues a green sample preparation for bioanalysis. As a proof-of-concept of this new methodology, cortisone and cortisol were determined in human saliva using a composite material made of a reversed phase polymer (Strata™-X-RP) and CoFe₂O₄ magnetic nanoparticles. Liquid chromatography coupled to tandem mass spectrometry was used to measure both analytes obtaining good analytical features in terms of linearity (R² > 0.997), method limits of detection and quantification (22.6 and 75.5 ng L^-1 for cortisone, and 19.3 and 64.3 ng L^-1 for cortisol, respectively), repeatability (RSD ≤11%) and relative recoveries (78-134%).