Bead-injection protocols for automated solid phase microextraction with sorbent renewal for each assay [Reproduced from https://www.flowinjectiontutorial.com].a) Injection of a metered amount of particles or beads with reactive surfaces in the flow system followed by mechanical trapping or capture with the aid of external energy sources; b) Injection of a metered volume of sample; c) Interaction of analyte(s) with sorptive surfaces; d) Preconcentration of analyte(s) followed by detection of native species or derivatization products; e) Automatic removal of sorptive surfaces.