Microchannel devices switching

The microchannel or microfluidic devices used for flow switching in GC are new developments which became available due to progresses made in precise laser machining capabilities of metal films and appropriate metal surface deactivation solutions. The features required for these microchannels devices are laser cut into metal sheet (shims) with thicknesses from 20 to 500 pm. The resulting channel dimensions are similar to the conventionally fused silica... 

The ability to modulate electrochemical reactivity and effectively switch OFF the reaction was extended further by Wang and coworkers [174] to control, on-demand, the separation and detection processes in microfiuidic devices. In this work, the catalytic nickel nanowires were placed, reoriented and removed on-demand at the exit of the separation channel of the microfiuidic chip, offering unique possibilities for controlling externally, events inside and outside a microchannel. 

Wang et al. [183] reported fast analysis of preblast and postblast cations and anions by using NCE in 60 seconds. Low EOF of PMMA chip material facilitated the rapid switching between analyses of cations and anions using the same microchannel and run buffer, and provided rapid measurement of seven explosives-related cations and anions. Wang et al. [184] discussed the future development of an NCE device for the detection of triacetone... 

Fig. 12 Experimental demonstration for different switch modes, (a) The 1x4 microfluidic switch prototype device, (b) DI water starts being ejected, (c-f) show the single-output switch mode to single desired outlet, microchannel 1, microchannel 2, microchannel 3, and microchannel 4, respectively, (g) shows simultaneous multiple-output mode to two desired outlets, microchannels 1 and 4...

The design in this case-study prototype device remains an issue for the reversible motion of the liquid. This case-study prototype device could be effectively used for the one shot of liquid in both single-output and multi-output modes on demand. For continuous random switch function, another problem appears if we turn on microchannel X first and desire to next turn on only microchannel Y where X>T. In this continuous switch function, the microchaimel X -f 1) will be also turned on in this case-study prototype device. Anyway, above issues could be resolved via the two-way bubble actuator design [18, 19], which could make the fluid flow backward in the unwanted microchannel. In addition, this microfluidic switch has the potential to be integrated into a wider fluidic network system with stop valves or microflow discretizers which could be used for separation of liquid segments from a continuous source. 

To introduce the concept and design details, a schematic representation of the 1x4 microfluidic switch with one inlet port and four outlet ports as shown in Fig. 1 is taken as a case study here. This case-study device, as shown in Fig. 1, consists of an embedded heater, a capillary system with hydrophilic microchannels, and a specific arrangement of hydrophobic patches. This device could be expanded to 1 xN microfluidic switch via the similar design. Also the embedded heater could be replaced by electrolysis electrodes. In Fig. 1, Li represents the length of each hydrophobic patch in the microchannel /. From microchannel 1 to 4, Li decreases with an increase of patch number in each microchannel. For the device design shown in Fig. 1, there are 1, 2, 3, and 4 separated hydrophobic patches in microchannel 1, 2, 3, and 4, respectively. These distributed patches have the same length in each microchannel. 

Figure 2.153 MicroChannel switching device used for GC-MS detector flow switching (DFS, Dual Data flow switch, Thermo Fisher Scientific).

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