Microcolumns beads packed

Beads packed in microcolumns is the most reported in literature, since users can customize the quantity of resin according to the capacity of it, to the volume of sample to be loaded, and to the minimum detectable activity (MDA) of the detector used. In general, packing is manually replaced in flow systems based on flow injection analysis G A), sequential injection analysis (SIA), multisyringe flow injection analysis (MSFIA) and multipumping flow systems (MPFS). By the contrary, lab on valve (LOV) allows the manipulation of heterogeneous solutions, i.e. bead injection, achieving the automated replacement of the resin. In Chapter 3 are described in detail the parts of the microcolumns and the way to fill them. Table 8.1 summarizes the variety of available resins from TrisKem International [4]. 

The ability to prepare monoliths within a mold of any shape was used by Lee et al. [128] who prepared monolithic ST-DVB microbeads within pulled fused silica needles and used them for the reversed-phase separation and on-line electrospray ionization mass spectrometry (ESI-MS) detection of proteins and peptides. As illustrated by Fig. 18, these monolithic microcolumns separated proteins far better than capillaries packed with commercial C18 silica or polymeric beads. 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

Online sorptive preconcentration exploiting renewable solid surfaces, the so-called bead injection (Bl), in the miniaturized LOV platform has been hyphenated to GC separation with electron-capture detection for automated determination of trace levels of PCBs in solid-waste leachates. To this end, the MSFIA system presented in Chapter 3, Figure 3.19, has been implemented. It comprises a mul-tisyringe burette, an extra solenoid valve, an LOV, and an injection valve (IV) as well as reversed-phase copolymeric beads with hydroxylated surface (Bond Elut Plexa) included into the channels of a poly(ether imide) LOV microconduit, thus serving as a transient microcolumn-packed reactor for preconcentration of organic species [194]. 

The use of LOV allows the bead injection process, so that the replacement of the resin packing was performed automatically. Contrary to the longer manual protocol to isolate Sr which lasts days, the automatic separation and preconcentration system allowed analyzing up to five samples per hour depending on the preconcentrated volume. The analytical protocol started with the automatic filling of the microcolumn with Sr-resin. Then it was conditioned with 2 ml of 8 mol/1 nitric acid. Once the column was ready, a variable volume of sample was dispensed toward the column. An additional volume of 0.5 ml of conditioning solution was propelled in order to eliminate interferences. After that, the elution of Sr was carried out dispensing 5.1 ml of 0.01 mol/1 nitric acid. For the radiostrontium quantification, the eluate was dried and measured in a LBPC. 

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