Both assay  protocols begin with injection of small amount of microspheres into a carrier stream (A). Next, sample comprising matrix and target analyte  is injected and transported downstream (B) where beads are packed in a well-defined geometry. When the sample zone reaches the packed bead layer (C), functional groups on the bead surfaces capture analyte molecules (yellow). As the sample zone moves away (D), the matrix material is washed out, leaving   the captured analyte on the beads. Analyte is either eluted from the beads (E) or detected on the beads (F). Beds can be either discarded (G) or retained for next assay cycles.

Analyte eluted from microcolumn was most frequently monitored by UV-VIS spectrophotometry (Vidigal 2013, Horskotte 2013), although fluorescence atomic adsorption (Hansen 2001, Miro 2008) and mass spectrometry (Ogata 2002) were also used.

Analyte retained on microcolumn was quantified by UV-VIS spectrophotometry and by fluorescence (Lacy 1990, Miro 2014). This method is method more difficult to perform, because reproducibility of results critically  depends on the volume and geometry of monitored beads. It offers a unique feature: monitoring of liquid/solid interactions in real time (3.4.3.C.).
Assay Protocols: Renewable Column and Spectrophotometry on Beads

J. Wang & E.H .Hansen Atomic Spectroscopy 22, 312 (2001)
Y. Ogata,, Anal. Chem., 74, 4702, (2002)
S. S. M. P. Vidigal, I. V. Toth and A. O. S. S. Rangel “Sequential injection lab-on-valve platform as a miniaturization tool for solid phase extraction.  Anal. Methods, 2013, 5, 585
M. Miro , S. K. Hartwell, J.  Jakmunee, K. Grudpan, E. H. Hansen “Recent developments in automatic solid-phase extraction with renewable surfaces exploiting flow-based  approaches’ TrAC 27 (2008) 749
B. Horskotte, P. Chocholous, P. Solich,” Large volume preconcentration and determination of nanomolar concentrations of iron in sea water using a renewable cellulose 8-hygroxyquinoline sorbent microcolumn and universal approach of postcolum eluate utilization in lab-on-valve system. Talanta 150 (2016) 213.
N Lacy, G.D. Christian J. Ruzicka  “‘ Enhancement of flow injection optosensing by sorbent extraction and reaction rate measurement”  Anal. Chem. 62, (1990) 1482.
M. Miro “ On chip microsolid –phase extraction in disposable sorbent format using mesofluidic platforms” TrAC 62. (2014) 154.