Microcapillary flow

Plastic microcapillary flow disk (MFD) reactors have been constructed from a flexible, plastic microcapillary film (MCF), comprising parallel capillary channels with diameters in the range of 80-250 jxm. MCFs are wound into spirals and heat treated to form solid disks. These reactors are capable of carrying out continuous flow reactions at elevated temperatures and pressures with a controlled residence time. ... 

Homung, C.H., Mackley, M.R., Baxendale, I.R. and Ley, S.V. (2007) A microcapillary flow disc reactor for organic s3mthesis. Organic Process Research Development, 11, 399 05. 

Of practical interest for micropumps, we also study the effect of the chaimel wall and packing particles on the overall electroosmotic flow rate in a microcapillary. Flow rate versus applied external electric field, for different packing particle sizes and the zeta potential ratio w/Cp> is plotted in Fig. 5. It is noted that the flow rate increases linearly with increasing applied voltage. For larger packing particles, the flow rate is... 

DETECTION OF MICROGELS IN EOR POLYMERS USING MICROCAPILLARY FLOW... 

Fig. 8 An illustration of experimental set up using a microcapillary flow reactor. ...

A Displacement Flow Immunosensor for Explosive Detection Using Microcapillaries, Anal. Chem. 1997, 69, 2779. 

A micromixer in which the fluid can be stirred by periodically pumping through the side channels is shown in Figure 3.45 [481]. The periodic perturbation applied via the side channel allows liquids A and B to be mixed. Other mixers based on oscillating pressure-pumped flow have also been reported [482,483]. Two droplets (600 pL) were merged and mixed by a push-pull (shuttling) method in a PDMS device consisting of a hydrophobic microcapillary vent (HMCV) [364]. 

The laminar stationary flow of an incompressible viscous liquid through cylindrical tubes can be described by Poiseuille s law this description was later extended to turbulent flow. Flowing patterns of two immiscible phases are more complex in microcapillaries various patterns of liquid-liquid flow are described in more detail in Chapter 4.3, while liquid-gas flow and related applications are discussed in Chapter 4.4. 

Anthocyanins help maintain microcapillary integrity by stabilizing the capillary walls. Blocked or reduced oxygen followed by the reestablishment of normal supplies is called ischemia-reperfusion . Ischemia-reperfusion could create the oxidants which result in white blood cell adhesion to the microcapillary walls, increase the capillary wall permeability, reduce the blood flow, and often cause permanent capillary damage. 

To produce the fine tip of the micropipette necessary for inserting into a cel 1, a microcapillary is put under tension in the axial direction and then the glass is heated near the middle until it becomes red-hot. Remarkably, as the heated glass flows and the microcapillary is thus stretched and necks down to the extremely fine diameter required (much less than the thickness of a human hair), the inside hole is maintained (the microcapillary eventually breaks where it was heated, forming two micropipettes). The inside of the micropipette is filled with oil for a pressure probe or filled with a conducting solution for electrical measurements (e.g., Fig. 3-6). 

Microcapillary (0.200 -s- 0.300 mm diameter) and nanocapiUary (0.075 -t- 0.100 mm diameter) columns limit solvent consumption and interface more easily with mass spectrometer detectors. They can assay only small amounts of sample and are superior for managing Joule heating due to their enhanced surface area to volume ratio and lower volumetric flow rate (uL/min) for a given linear mobile phase velocity (mm/sec). 

Cf-FAB in all its forms is a low flow-rate technique, i.e., 1-15 pl/min. Therefore, one should use either a microbore or packed microcapillary column, or a conventional colunm in combination with a post-column splitting device [47-48]. 

A 5-20-pm-lD micro-ESl needle was described by Eimnett and Caprioli [70]. The flow-rates used were 0.3-6.4 pEmin. Similar needles were successfully made by other as well. Robins and Guido [71] reported an integrated packed 150-250-pm-lD microcapillary LC coluitm-micro-ESl device. A Teflon frit retains the coluttm packing material. The last part of the fused-silica colirnm tubing is drawn into a sharp tip to act as an ESI emitter. 

From a practical point of view, the discussion on flow-rate can be summarized as follows. In LC-APCI-MS, the typical flow-rate is 0.5-1.0 ml/min. For routine applications of LC-ESI-MS in many fields, extreme column miniaturization comes with great difficulties in sample handling and instrument operation. In these applications, LC-MS is best performed with a 2-mm-ID column, providing an optimum flow-rate of 200 pFmin, or alternatively with conventional 3-4.6-mm-ID columns in combination with a moderate split. In sample limited cases, further reduction of the column inner diameter must be considered. Packed microcapillary and nano-LC columns with micro-ESI and nano-ESI are rontinely applied inproteomics stndies (Ch. 17.5.2). 

The column inner diameter is determined by the amount of sample available and the LC-MS interface selected, tn general, flow-rates between 200 and 400 pl/min are considered optimum for (pneumatically-assisted) ESt. This explains the frequent use of 2-mm-ID columns, tn sample-limited analysis, e.g., in the analysis of mouse plasma samples, microbore (1 mm ID) or packed-microcapillary columns (320 pm ID) are applied at relatively low flow-rates [12-13]. For APCt, 4.6-mm-tD columns are preferred, operated at typically 1 ml/min. The LC system should provide symmetric peaks with a width that enables the acquisition of tO-20 data points for each compound in order to enable an accurate determination of the peak area. 

For consistent application of solutions to a TLC plate, gently touch a microcapillary containing the analyte solution to the surface of the plate and allow a small portion of the aliquot to flow out. Moving parallel to the baseline of the plate, apply the solution in a narrow band about 0.5 cm long. Upon development of the plate, tight, narrow bands are formed, making visualization of trace impurities easier [2]. 

Keywords Continuous flow PCR DNA analysis DNA microarrays Genetic analysis Integrated microsystems Microcapillary electrophoresis Microfluidics Micro-PCR devices Solid-phase extraction... 

Fig. 5 Determination of the chemotactic sensitivity of E. colt, (a) Schematic of the microfluidic device. Chemoattractant and fluorescein were injected in the microcapillary via inlet C by means of a passive valve, (b) Flow in the main channel (from A to B) was used to transport E. coll past the entrance (M) of the microcapillary, (c, d) Epifluorescence images of the microcapiflary filled with...

To analyze the flow through a porous medium, we can, as before, model the medium as a collection of parallel cylindrical microcapillaries. As noted in Section 4.7, the actual sinuous nature of the capillaries may be accounted for by the introduction of an empirical tortuosity factor. The results for electroosmotic flow through a capillary are then readily carried over to the porous medium by using Darcy s law (Eq. 4.7.7) and, for example, the Kozeny-Carman permeability (Eq. 4.7.16). 

Figure 7.25 Capillary electrophoresis, (a) Schematic of microcapillary dimensions, (b) Ion-solute structure at the capillary wall, (c) Schematic illustration of electro-osmotic flow (EOF) created in the microcapillary as a result of capillary bore surface charges.

These have mainly been developed by McGuffin and Novotny [120] and coworkers and are characterised by low column diameter to particle size ratios of 2 to 5. This is much less than small bore packed columns (50-200) or conventional columns (500-2000). Below ratios of 2, it has been reported [101] that the packing structure collapses under the viscous flow and causes clogging of the column. The microcapillary columns are prepared by extruding a heavy walled glass tube, 0.5-2 mm i.d., packed with 10-50 pm particle size high temperatures resistant silica or alumina. For reverse phase work the stationary phases have then to be bonded in situ. 

Despite the numerous advantages the instrumental demands of microcolumn LC are considerable, and these demands are further accentuated as the requirements vary from one column type to another. A consequence of the reduced flow rates is that the detector flow-cell volume should be reduced to <10nl for OTCs, 0.1 pi for packed microcapillaries and 1 pi for microbore columns. An additional demand of the detector is that it should have a rapid response, <0.5 s. Development of suitable detectors is paramount if the potential of micro-LC is to be realised. Study of detector systems has focused in two areas firstly, the miniaturisation of ultraviolet, fluorescence and electrochemical systems, using in the former two systems LASERS as excitation sources and ultraviolet fibre optic and on-line cells to reduce band broadening and increase sensitivity [123,124] secondly, the direct interfacing with systems which previously required transport and/or concentration of the eluant. Interfacing of HPLC with mass spectroscopy has been undertaken by Barefoot et al. [125] and Lisek et al. [126] and flame systems (FPD and TSD) have been reviewed by Kientz et al. [127]. Jinno has reviewed the interfacing of micro-LC with ICP [128]. 

Histograms for a solution of Cy5-dCTP flowing through a microcapillary are shown in Fig. 5.126. The integration time per step of the sequence was 0.5 ms. The total number of steps was 204,800, resulting in a total acquisition time of 102.4 seconds. 

Narang U., Gauger P. R., Ligler F. S., A displacement flow immunosensor for explosive detection using microcapillaries, A a/. Chem., 69, 2779-2785, 1997. 

Yen, B.K.H., N.E. Stott, K.F. Jensen, and M.G Bawendi, A continuous-flow microcapillary reactor for the preparation of a size series of CdSe nanocrystals. Advanced Materials, 2003,15 1858-1862. 

Bianchi, F., Wagner, F., Hoffmann, P., and Girault, H. H., Electroosmotic flow in composite microchannels and implications in microcapillary electrophoresis systems. Anal. Chem., 73, 829, 2001. 

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