Micro-valves

More than 100 micro structured devices are listed on the homepage of the pChemTec consortium [24]. The devices cover physical applications such as flow distribution, mixing, heat transfer, phase transfer, emulsification and suspension, as well as chemical applications such as chemical and biochemical processing. Some separation units such as membrane separation and capillary electrophoresis are also offered. Control devices such as valves, micro pumps for product analysis and mass flow controllers supplement the catalog. 

Jannasch, H.W., Mcgill, P.R., Zdeblick, M., Erickson, J., Integrated micro-analyzers with frozen plug valves. Micro Total Analysis Systems, Proceedings 5th p7AS Symposium, Monterey, CA, Oct. 21-25, 2001, 529-530. 

The regulation of the gaseous atmosphere is ensured by several valves (micro leaks). Two of them are linked to the gaseous circuit, and allow us to independently inject two gases in the reactor. 

Carlen ET, Mastrangelo CH (2000) Paraffin actuated surface micromachined valves, micro electro mechanical systems, 2000, MEMS 2000. In The thirteenth annual international conference, Miyazaki, Japan, pp 381-385... 

Lab-on-valve micro-machined device, placed atop a multi-position valve, containing mesofluidic channels where solutions or suspensions are handled by means of a syringe pump. 

O-. . "-. . Transitional Flow / Micro Gyroscope — Accelerometer Micro Valves Micro Nozzles 0 Flow Sensors... 

In this section, the basic building blocks of xTAS are considered to be available or at least, the fabrication of these blocks is considered to be feasible. With basic building blocks, subsystems of liTAS are meant that are capable of performing a well-defined function, like inlet, selection valve, micro-pump, injector, mixing chamber, reaction chamber, outlet, etc. It will be shown that with the availability of these subsystems, the performance of the coulometric sensor-actuator device can be essentially improved. 

Iridium Oxide. Iridium dioxide [12030 9-8] coatings, typically used in combination with valve metal oxides, are quite similar in stmcture to those of mthenium dioxide coatings. X-ray diffraction shows the mtile crystal stmcture of the iridium dioxide scanning electron micrographs show the micro-cracked surface typical of these thermally prepared oxide coatings. 

Figure 6.10 Schematic diagram of a typical interface used for on-line SFE-CEST coupling (from ref. 57) 1, micro-LC pump 2, heated resti ictor 3, six-poit valve 4, sample concentrator 5, three-port valve 6, CE instmment.

Different approaches utilizing multidimensional EC or SEC systems have been reported for the analysis of middle distillates in diesel fuel. A method, based on the EC separation of paraffins and naphthenes by means of a micro-particulate, organic gel column has been described (23, 24). The complete system contained up to four different EC columns, a number of column-switching valves and a dielectric constant detector. However, the EC column for the separation of paraffins and naphthenes, which is an essential part of the system, is no longer commercially available. 

Multidimensional LC has also been used to determine ursodeoxycholic acid and its conjugates in serum (14). These compounds are used in the treatment of cholesterol gallstones, hepatitis and bilary cirrhosis. These authors employed a traditional (10 X 4 mm) pre-column and a micro-bore (35 X 2 mm) analytical column that were interfaced by using a six-port switching valve. 

The whole set-up for partial oxidation comprises a micro mixer for safe handling of explosive mixtures downstream (flame-arrestor effect), a micro heat exchanger for pre-heating reactant gases, the pressure vessel with the monolith reactor, a double-pipe heat exchanger for product gas cooling and a pneumatic pressure control valve to allow operation at elevated pressure [3]. 

Figure4.62 Experimental set-up for liquid/liquid experiments (a) reservoir for the substrate in n-heptane (b) water reservoir (c, d) high-pressure liquid pumps (e) HPLC injection valve with sample loop for catalyst injection (f) micro mixer ...

A stream of ethylene is fed into the reactor by use of quaternary LC pumps and subsequently dissolved in a 1.90 ml h toluene stream [1]. Ethylene is handled at 60 °C, well above the critical temperature. Catalyst additions are fed via HPLC-type sample injection valves. Various combinations of precatalysts and activators were sampled and loaded by an autoinjector. Catalyst solutions typically were diluted 20-fold within the micro reactor. 

Figure 5.28 Schematic of the experimental set-up. Water/ethylene glycol/SDS reservoir (a) high-pressure liquid pumps (b) catalyst/ substrate HPLC injection valve with 200 pi sample loop (c) hydrogen supply, equipped with mass flow controller (d) micro mixer (e) heating jacket (f) tubular glass or quartz reactor (g) back-pressure regulator (h) [64],...

FIGURE 16.5 Schematic of instrumental setup for 2D micro-RPLC-CZE. A split injection/ flow system is used to deliver a nanoliter per second flow rate to the micro-RP-HPLC column from the gradient LC pump. The HPLC microcolumn has 50 pm i.d. and 76 cm length, and the electrophoresis capillary has 17 pm i.d., L — 25 cm, and/= 15 cm. The valve is air-actuated and controls the flow of flush buffer (reprinted with permission from Analytical Chemistry). 

After the activation period, the reactor temperature was decreased to 453 K, synthesis gas (H2 CO = 2 1) was introduced to the reactor, and the pressure was increased to 2.03 MPa (20.7 atm). The reactor temperature was increased to 493 K at a rate of 1 K/min, and the space velocity was maintained at 5 SL/h/gcat. The reaction products were continuously removed from the vapor space of the reactor and passed through two traps, a warm trap maintained at 373 K and a cold trap held at 273 K. The uncondensed vapor stream was reduced to atmospheric pressure through a letdown valve. The gas flow was measured using a wet test meter and analyzed by an online GC. The accumulated reactor liquid products were removed every 24 h by passing through a 2 pm sintered metal filter located below the liquid level in the CSTR. The conversions of CO and H2 were obtained by gas chromatography (GC) analysis (micro-GC equipped with thermal conductivity detectors) of the reactor exit gas mixture. The reaction products were collected in three traps maintained at different temperatures a hot trap (200°C), a warm trap (100°C), and a cold trap (0°C). The products were separated into different fractions (rewax, wax, oil, and aqueous) for quantification. However, the oil and wax fractions were mixed prior to GC analysis. 

D-machining techniques of semiconductor materials are amongst the core processes leading to the miniaturized structures (sensors, actuators (e.g. valves, relays, etc.) and passive components (e.g. micro channels)). 

The concept of an integrated micro-fluidic-based system has now been developed (Zhang et al. 2006), with an example shown in Fig. 7. This particular system is based on conventional chromatographic instrumentation and employs a multi-valving system, located between two syringe pumps, shown in the foreground, to enable the introduction of multiple reagents from an auto-sampler to be loaded onto the micro-reactor. Because of the low diffussional distances obtained in this sys-... 

In general, the apparatus for titrimetric analysis is simple in construction and operation. A typical analysis procedure would involve measurement of the amount of sample either by mass or volume, and then addition of the titrant from a burette or micro-syringe. Apart from visual indication, the course of a titration may be followed by electrochemical or photometric means in neither is the equipment required complex. A simple valve voltmeter or conductivity bridge will suffice on the one hand, and a simple spectrophotometer or filter photometer with minor modifications on the other. Varying degrees of automation may be incorporated. 

The maximum injection volume depends on the volume of the sample loop in the injection valve. The reproducibility of manual injection depends on the skill of the operator. The use of a small sample loop and an overflow injection of the sample solution so that the loop is fully flushed with sample are basic requirements for quantitative analysis. The highest injection reproducibility can be obtained by an auto-injector with a fixed sample loop. The smallest reasonable injection volume is 1 (A. A nl-scale injection valve can be constructed however, the memory effect at the surface of contact parts affects quantitative analysis compared with the use of a /d-scale injection valve. For a semi-micro system, a low hold-up volume injection valve is desired. The minimum injection volume is 80 nl. For a preparative-scale injection, the sample loop can be easily replaced with a larger-volume loop, such as a 200 jA, instead of the standard 20 /A loop. 

The separation of a mixture of aromatic compounds (benzene, naphthalene, anthracene, chrysenes, and benz(a)pyrene) at 31 bar is shown in Figure 3. This chromatogram was obtained with a Perkin Elmer Model 250 ultraviolet detector with the high-pressure cell placed after the cooling heat exchanger and before the flow control valve. A similar chromatogram is obtained with an Isco Model UAA with a 10 mm micro cell placed after the flow control valve. 

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