MEPS is a new format of miniaturized SPE, which was developed by Abdel-Rehim and his coworkers to work with small-volume samples (approximately 10–250 L) [13,14]. As shown in Fig. 2E, a small amount of a sorbent (approximately 1–4 mg) is packed into the microsyringe barrel or a container between the needle and the barrel, which is used as a mini SPE cartridge. Since MEPS processes the same working principle as SPE, SPE sorbents can be applied to MEPS and transferring a method from SPE to MEPS might be relatively straightforward [15]. The automated online MEPS-LC can be realized by connecting the syringe to an autosampler (e.g., CTCPAL autosampler), using a procedure similar to in-tube SPME that
is performed by drawing and ejecting samples. Due to the small amount of sorbents, only small volume of solvents is needed for
elution (usually less than 50 L) [16–22]. Thus, the whole eluent
can be directly transferred to LC injector for determination, facilitating
the online analysis. Compared with SPME, a non-exhaustive
extraction technique, MEPS exhibits higher recovery, sensitivity
and speed [14].