Lab-on-valve Flow Injection Analysis

Lab-on-valve (LOV) is a development of FI A whereby a microchannel chip (microconduit) is combined with a switching valve. It is a type of pTAS system. The function of the 

While LOV can have similar applications to LOG, it has found a particular niche in online sample pretreatment methods where the valve allows automation and miniaturisation of these traditionally labour intensive steps. Examples include solid phase extraction, ion exchange and solvent extraction. Compared to macrosample pretreatment, LOV offers the following advantages  

Disadvantages of LOV can include clogging, which because of the small channel dimensions can be a big problem if even fine particles are introduced. Hence, filtering of sample prior to analysis on chip is a requirement. Another issue can be the incompatibility 

Some of the interesting applications of LOV inclnde the manipnlation of beads and microcolnmns for sample clean-up or separation. In particnlar, one version of the system has received considerable attention and is called microseqnential injection-lab-on-valve (pSl-LOV). The J,SI-LOV device can be used for sample pretreatment alone or in seqnence with analysis and detection (usually absorbance or flnorescence). It has also been employed as the front end of a miniaturised CE system. An interesting nse of J,SI-LOV has been in conjunction with suspensions of specially coated beads. These beads can be manipulated by the multiport valve to flow into the holding coil and from there into the detector flow cell to form a temporary microcolnmn. The sample is then mixed with the bead column and any reactions are detected, e.g. adsorption over time. After measurements have been made, the beads are sent to waste. The formation and removal of these temporary microcolumns has advantages over the nse of fixed colnmns snch as  

The bead snspension is held between two outlets containing small PEEK tnbing fittings, which allow liqnids to flow freely bnt entrap the beads. A syringe pnmp is nsed to pnmp the beads into the temporary microcolumn. These bead colnmns can be nsed in many ways in the LOV system - from solid phase extraction to reaction columns. 

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