Miniaturization capillary tubes

When trying to manipulate fluids on the micron scale, formidable problems have to be overcome [301], Miniature pumps, valves, switches, and new analytical tools have to be developed. To illustrate this we discuss the fundamental problem of transporting a liquid through a capillary tube. In the macroscopic world we would apply a pressure AP between the two ends. According to the law of Hagen-Poiseuille the volume of liquid V transported per time t is (assuming laminar flow)... 

Figure 8 Illustration of whole-column imaging miniaturized capillary isoelectric focusing instruments with a LED as light source. A 1.2-cm capillary is used as a separation column for focusing. The outside polyimide coating of the capillary is removed, and the inside surface of capillary is coated with non-cross-linked polyacrylamide to eliminate electroosmotic flow. The two ends of the capillary are connected with inlet and outlet capillaries (with the same i.d. and o.d. as the separation capillary) by two pieces of porous hollow fiber. Two glass tubes are used as electrolyte tanks and glued directly on the glass slide by epoxy glue. The two pieces of hollow fiber are in the electrolyte tanks. The length of the capillary between the two electrolyte tanks is about 0.9 mm.

A miniaturized luminometer consists of four micro-dispensers, four micro-cells, and a photodiode array (Fig. 1(a)). The micro-dispensers consisted of capillary tubes placed in each cell. A high photoemission collecting efficiency was about 7% because the photodiode array was closely positioned under the micro-cells. Bioluminescence from the micro-cells was simultaneously detected with the photodiode array (HAMAMATSU SI 133-01, Japan) placed on a base plate that had in-house-made amplifiers. A multifunctional DAQ (National Instruments PCI-MIO-16XE-50, TX, USA) and National Instruments Lab VIEW 6i were used for... 

Schlotterbeck G, Ross A, Hochstrasser R, Senn H, Kuhn T, Marek D, Schett O. High-resolution capillary tube NMR. A miniaturized 5 mL high-sensitivity TXI probe for mass-limited samples, off-line LC NMR, and HT NMR. Anal Chem 2002 74 4464-A471. 

CE can be operated in several modes. The approach described in the previous paragraph is referred to as capillary zone electrophoresis, or CZE. A variant called capillary gel electrophoresis uses a capillary tube filled with gel, essentially a miniaturized version of slab-gel techniques. The third variant, and the one of most forensic significance, is micellar electrokinetic chromatography (MEK or MECK). MEK is a modification designed to improve the separation of neutral spedes, which are easily separated from cations and anions, but not well separated among themselves. 

Schlotterbeck, G., Ross, A., Senn, H., Hochstrasser, R., Tschirky, H., Seydonx, R., Marek, D., Kiihn, T., Schett, O., and Warden, M. (2001) High resolution NMR in capillary tubes a new miniaturized 1mm TXI Probe, ENC, Orlando, Florida 11-16 March, Poster presentation. 

Microfabrication techniques with the features of integration, reproduction and precision are particularly suitable for the implementation of miniaturized designs and significant reduction in product costs. A miniaturized magnetic resonance probe for on-line/in-line flow studies can be microfabricated by combining an rf coil [45, 46] with microfabricated gradients [47] and electronics [48] around a small tube/capillary. 

Further miniaturization of the SPE technique permits a reduction in the amount of organic solvent used, on-line coupling to analytical instruments, fast analysis times and excellent sensitivity. Downsizing of SPE has been focused mainly on the use of libers, beads, and adsorbents as extraction phases that are reproducibly packed in tubes, capillaries, syringes, needles, and even micropipette tips. 

The nano-electrospray (nanoES) source is essentially a miniaturized version of the ES source. This technique allows very small amounts of sample to be ionized efficiently at nanoliters per minute flow rates and it involves loading sample volumes of 1-2 pi into a gold-coated capillary needle, which is introduced to the ion source. Alternatively for on-line nanoLC-MS experiments the end of the nanoLC column serves as the nanospray needle. The nanoES source disperses the liquid analyte entirely by electrostatic means [27] and does not require assistance such as solvent pumps or nebulizing gas. This improves sample desolvation and ionization and sample loading can be made to last 30 minutes or more. Also, the creation of nanodroplets means a high surface area to volume ratio allowing the efficient use of the sample without losses. Additionally, the introduction of the Z-spray ion source on some instruments has enabled an increase in sensitivity. In a Z-spray ion source, the analyte ions follow a Z-shaped trajectory between the inlet tube to the final skimmer which differs from the linear trajectory of a conventional inlet. This allows ions to be diverted from neutral molecules such as solvents and buffers, resulting in enhanced sensitivity. 

Two kinds of conductivity detector are distinguished contact detectors and contactless detectors. Both types were originally developed for isotachophoresis in 0.2-0.5-mm-inner diameter (i.d.) PTFE tubes. Contactless detectors are based on the measurement of high-frequency cell resistance and, as such, inversely proportional to the conductivity. The advantage is that electrodes do not make contact with the buffer solution and are, therefore, outside the electric field. As these types of detectors are difficult to miniaturize down to the usual 50-75-jU.m capillar inner diameter, their actual application in capillary electrophoresis (CE) is limited. 

Steel capillary with nitrogen gas flowing through the space between the two capillaries. Insertion of the miniaturized nebulizer into the end of the drift tube and its contact with the heated wall of the drift tube, the purpose of which is to preheat the nebulizer gas, allows faster system equilibration at startup and production of a more stable and homogeneous aerosol. 

Miniaturization Application of lasers as light sources resulted in a reduction in the size of refractive index detectors and made them compatible with in-line monitoring systems that are needed in capillary separation technology. The refractive index of minute amounts of solution may be determined by the measurement of the diffraction phenomenon produced in the interaction between the laser beam and a fluid-filled capillary. The laser beam passing through an off-center capillary produces a fan of scattered light in the plane perpendicular to the tube axis. The position of a single line corresponds to the refractive index of the fluid within the tube... 

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