FIAlab Instruments
 Leaders in Flow Injection Technology

Injection of a well defined quantity of beads and their capture in a desired section of a flow channel are the key operations for a successful performance of Bead  Injection based assays. The bead injection is accomplished by aspirating beads from a well stirred container placed atop LAB-ON-VALVE.  Beads are captured  in a “Jet Ring” flow geometry within a conduit, the end of which blocked by a rod, having the external diameter smaller then the internal diameter of the channel. Typical  dimensions are: channel i.d.  1630, rod o.d., 1600 leaving ring formed gap of 15 which will retain beads of o.d. larger than 40 ( all dimensions in micrometers). The ring formed gap allows liquid to pass through, thus forcing a perfectly symmetrical flow through the column of packed beads. When the beads are to be discarded, the flow is rapidly reversed so that the jet of liquid forces the beads upstream, either in next desired location or into the waste. The jet ring configuration, in contrast to frits or filters is not clogged by beads.

Bead Injection Spectroscopy is based on monitoring of the change of UV-VIS absorbance or fluorescence of captured beads, as their functional groups react with analyte molecules present in the stream flowing through the packed layer.( Literature ref 1, 4 and 7) For this purpose  beads are captured within the flow cell, where one of the optic fibers is sheated in a casing  of 1600 micrometers o.d., serving as a plug. The flow cell is packed with beads by forward flow and “unpacked” by flow reversal. Absorbance or fluorescence configuration of the jet ring flow cell are possible within multipurpose flow cell,  since its dimensions are  fabricated  to appropriate dimensions, making the LAB-ON-VALVE  suitable for both Sequential and Bead Injection methodology. 

Renewable Microcolumn  technique uses external detector systems such as electrothermal atomic absorption spectrometry (ETAAS), mass spectrometry or polymerase chain reaction for the assay of the analyte. Thus, serving as a “front end”, for analyte accumulation and  purification, the beads are after injection packed into a microcolumn ( up to 9 mm long , 1.6 mm o.d. ) situated within the LAB-ON-VALVE structure. Packed beads  are being held in place by 3mm PEEK rod ( shown in red) , that rests , at forward flow,  against the end of the tubing secured at the periphery of the LAB-ON-VALVE module by a standard fitting. When the microcolumn is to be discarded, or moved into another location, the flow is rapidly reversed so that the resulting jet of liquid  flushes the beads in  desired location. “Unpacking” of the bead column  is assisted by the movement of the rod it  can slide back and forth within the straight section of the conduit. The movement of the rod cleans the ring formed gap, thus preventing clogging.

 For ETAAS application, the liquid segment containing beads needs to be  transported  from the FIAlab-on-valve  instrument into the graphite furnace, where the beads are pyrolised and the analyte is atomized for measurement. This is accomplished by sandwiching the liquid segment with air. (Literature ref.6) 

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