Pumps restrictors

Vapor Pressure. The Shiley Infusaid implantable infusion pump utilizes energy stored in a two-phase fluorinated hydrocarbon fluid. The pump consists of a refillable chamber that holds the dmg and a chamber that holds the fluid. The equiUbrium vapor pressure of the fluid, a constant 60 kPa (450 mm Hg), compresses the bellows, pumping the dmg through a bacterial filter, a capillary flow restrictor, and an infusion cannula to the target body site (56,116). 

Figure 6.12 Schematic diagram of the interface used for direct SFE-CEST coupling without a sample pre-concenti ation step 1, micro-LC pump 2, heated restrictor 3, six-port valve 4, direct by-pass to the CE unit 5, three-port valve 6, CE instmment. (from ref. 58).

The instrumental requirements for supercritical fluid extraction are quite simple. A pump is essential to generate the extraction pressure in a themostated extraction vessel. The soluble sample components are then swept from the vessel through a flow restrictor into a collection device that is normally at ambient pressure. The fluid used for supercritical fluid... 

The basic SFC system comprises a mobile phase delivery system, an injector (as in HPLC), oven, restrictor, detector and a control/data system. In SFC the mobile phase is supplied to the LC pump where the pressure of the fluid is raised above the critical pressure. Pressure control is the primary variable in SFC. In SFC temperature is also important, but more as a supplementary parameter to pressure programming. Samples are introduced into the fluid stream via an LC injection valve and separated on a column placed in a GC oven thermostatted above the critical temperature of the mobile phase. A postcolumn restrictor ensures that the fluid is maintained above its critical pressure throughout the separation process. Detectors positioned either before or after the postcolumn restrictor monitor analytes eluting from the column. The key feature differentiating SFC from conventional techniques is the use of the significantly elevated pressure at the column outlet. This allows not only to use mobile phases that are either impossible or impractical under conventional LC and GC conditions but also to use more ordinary... 

In reduced-flow LC-MS systems, the solvent flow into the spectrometer is reduced to a level where the pumping system can cope. Essentially, three such systems have been developed direct-liquid-introduction (DLI), flowing FAB [531] and electrospray [532]. An alternative approach to belt transport interfacing is to deliver the column eluate directly into the MS source and use Cl techniques. Methods based on this principle are called direct-liquid-injection systems, which are comprised of capillary flow restrictors, diaphragms,... 

Using a 1000 psi flow restrictor coil (length of 0.007" i.d. tubing), again pump the water at ImL/min. After the flow has stabilized, record the high and low pressure points for a period of time (typically, 1 min). The high and low points should vary by less than a specified amount (e.g., <30 psi). 

Application of SFE necessitates a CO2 source, a pump to pressurize the fluid, an oven containing the extraction vessel, a restrictor to maintain a high pressure in the extraction line, an analyte collection vessel, and an overall system controller. CO2 is drawn from the bottom of the tank with a dip tube because the liquid is the more dense of the two phases. The substantial vapor pressure of the CO2 at ambient temperature helps to displace the liquid into the pump. CO2 remains a liquid throughout the pumping or compression zones and passes through small-diameter metal tubing as it approaches the extraction vessel. A preheating zone in front of the extraction vessel allows supercritical temperature, pressure, and density conditions to be applied immediately to the analyte matrix in the vessel. 

In SFC, the mobile phase is initially pumped as a liquid and is brought into the supercritical region by heating it above its supercritical temperature before it enters the analytical column. It passes through an injection valve where the sample is introduced into the supercritical stream and then into the analytical column. It is maintained supercritical as it passes through the column and into the detector by a pressure restrictor placed either after the detector or at the end of the column. The restrictor is a vital component it keeps the mobile phase supercritical throughout the separation and often must be heated to prevent clogging both variable- and fixed-restrictors are available. 

Figure 6.4—Schematic of a supercriticalfluid chromatograph. Carbon dioxide reaches a supercritical state between the pump and the injector. A pressure regulator (restrictor) is located after the column and either before or after the detector, depending on its type. It allows the mobile phase to be kept under supercritical conditions until its exit from the column.

Syrup is pumped from a BiB container or syrup reservoir by a pressure activated pump, through another cooling coil in the cooler and on to one of the dispense valves. When the valve is opened to dispense product, pressure in the syrup line drops and the pump is activated until the valve shuts. The ratio of syrup to carbonated water is adjusted by flow restrictors in the feed pipes to the valve. 

Supercritical fluid extraction system - Hewlett Packard Model 7680A totally automated system with unlimited-capacity reciprocating pump, specially designed extraction chamber with safety interlocks, a variable restrictor nozzle and analyte collection trap. The operation of the extractor is controlled by a personal computer which is a Microsoft Windows-based system. An animated status screen provides real-time monitoring of the extraction process. Table II gives the SFE conditions for the HP extractor. 

We have demonstrated in this paper that two and four samples can be extracted in parallel with supercritical carbon dioxide without significant impact on data quality. Modifications made to an off-line extractor involved addition of a multiport manifold for the distribution of supercritical fluid to four extraction vessels and of a 12-port, two-way switching valve that allowed collection of two fractions per sample in unattended operation. The only limitation that we have experienced with the four-vessel extraction system was in the duration of the extraction. When working with 2-mL extraction vessels and 50-/zm restrictors, and using the pressure/temperature conditions mentioned above, the 250-mL syringe pump allows us a maximum extraction time of 60 min. During this time, two 30-min fractions can be collected with the present arrangement. 

The bulk of the SFE experiments performed to date were executed with systems typically consisting of a syringe or reciprocating pump, a high-pressure containing sample vessel comprised of HPLC column hardware, and a fused silica capillary restrictor. Extraction vessel temperatures of 40-80°C were usually accomplished using a converted oven or with the use of a thermostatted tube heater (2,3). Instrument manufacturers now offer a variety of commercially available SFE systems that vary in design, operation, features, ease of operation, and limitations. 

Thimble Volumes. For these experiments the thimble volumes and the extraction times were held constant. To accomplish this, the mass flow of the system had to be varied by changing the flow rate at the pump head for each density step. Controlling the mass flow rate allowed the linear/volumetric flow to be consistent throughout the experiments. This is different from the paprika experiments in which the mass flow was held constant and the extraction times were changed, to keep thimble volumes constant for each extraction step. Flow control is one of the major advantages of variable restrictor based SFE units. 

Figure 7.2.4 Experimental set-up used for SFC-NMR experiments (a) modifier pump (b) SFC pump (c) CO2 cylinder with dip-tube (d) cryostat (e) GC oven with mixing chamber and separation column (f) injection valve (g) UV detector (h) NMR magnet (i) backpressure regulator or restrictor (j) hardware control unit...

Reactant feeds are generated by vaporizing liquid flows from HPLC pumps with manometric pulse dampeners or high-pressure syringe pumps and mixing this vapor with gas components metered through mass flow controllers. This reaction feed is then divided between the 48 channels equally by using flow restrictors such as silica capillaries or micromachined channels (Fig. 3.12). The capillaries feed into the inlet stand-offs of the reactor modules. 

Some support structures are also included for detachably retaining the various components of the system. Preferably the support structure can be of the assembly board type , which provides prearranged flow channels and connector ports. The desired components of the system can be fastened into these connectors by pins. The flow control system that makes up the ICS system can include pumps, flow channels, manifolds, flow restrictors, valves, etc. These components are equipped with the necessary fittings that allow them to be sealed with the prearranged or selectively located flow channels or connectors. The flow system can also include detachable mixing devices, e.g., static or ultrasonic, or with a chip-like design. The reaction units, whether chip-like or not, can be of thermal, electrochemical, photochemical or pressure type [84]. 

This vial could be placed in two positions by the inlet lift. In the lower position of the lift, EOF driven isocratic and gradient CEC was possible. The solvent was delivered by the pump to the vial through the inner channel and removed via the outer channel using a pressure of nitrogen (right panel of Fig. 2.11). The resistance of the outlet restrictor was low. The pressure in the vial equaled the external gas pressure and was the same in the outlet vial. In this way, no hydraulic flow was generated and bubble formation was suppressed. The column continuously accepted the delivered solvent from the vial by electroosmotic flow. In this position, the flow delivered by the external pump must be low to avoid solvent overflow in the vial. 

Huber et al. [43] used a commercial capillary electrophoresis system connected to a LC pump to achieve the gradient elution. His approach is shown in Fig. 2.14. Two LC pumps were connected to one end of a capillary restrictor through a static mixing T-piece. The other end of the restriction capillary was connected to an injection valve. This valve was connected to a poly (ether ether keton) (PEEK) cross (17.2 pL) which... 

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