Injection valves

Injectors introduce the sample into the mobile phase under high pressure. There are several approaches to injection in HPLC, such as syringe injection via septum, a combination of a septum and syringe or a valve injection. Valve injection is the method of preference in up-to-date HPLC instrumentation. 

Mixer 89 [M 89] Cantilever-valve Injection Micro Mixer... 

Figure 1.189 Schematic exploded views of the cantilever-valve injection mixer [33] (by courtesy of Kluwer Academic Publishers).

Mixer type Cantilever-valve injection mixer Distance fin-to-fin (underneath the cantilever), fin width 70 pm, 5 pm... 

Multi-port Valves, Injection Valves and Sensors... 

Poly (3-hexylthiophene) [103] Pulse valve injection of macromolecules in solution. Another way of depositing molecules onto the surface that cannot be evaporated. 

Figure 11 Experimental setup for analysis of substance P metabolism and its metabolic fragments. Substance P was infused into the rat striatum through a microdialysis probe at 0.3 (JlL/min, and the probe was used both to deliver and collect metabolic products. The microdialysate was sampled into a 10-port valve, injected into a fused-silica Cl8 column, and washed with 2% methanol—0.25% acetic acid. The peptides were eluted from the column with 50% methanol—acetic acid at 0.82 J,L/min directly into the microelectrospray source on the mass spectrometer by switching the valve back.

It consists of a ceramic cubic body, in which a cylindrical cavity is drilled. A channel is drilled perpendicular to the axis of the cavity and hosts two rods (electrodes) of the material to be vaporized, facing each other and separated by a gap of about 1 mm. A solenoid pulsed valve injects helium at the pressure of 20 bar through an insulating ceramic nozzle on the back of the cavity. The gap between the electrodes is off-axis, in such a way that the gas flushes on the cathode surface. A removable nozzle with cylindrical shape closes the front of the source. 

Valve, injection, 4-way, 0.20 and 0.50 mL injection loop 1 Valve, back pressure, Upchurch 1 Valve, back pressure, relief 1 Valve, flow switching... 

C range, at atmospheric pressure, and at N2/hydrocarbon ratio of 0.48. The products of the reaction were analyzed on line with a Varian-3400 gas cromatograh equipped with a FID detector, cryogenic oven, and automatic gas sampling valve injection, with a capillary column (DB-5, 50 m). 

Valves Injection molding, transfer molding, thermoforming PTFE, PVDF, PFA, ETFE, ECTFE... 

More advanced designs of the on-line preconcentration technique use sophisticated ion-exchange materials [576, 683, 684, 1217], time-based injection rather than valve injection [576, 712, 1228], and, most importantly, a countercurrent operation of the microcolumn [684, 712], an operation mode that prevents any matrix material from entering the flowthrough detector even during the preconcentration period. Thus, in Fig. 

Valve injection. Valve injection of the sample is now the preferred and accepted technique. Sample application is rapid, the solvent flow from the pump does not have to be stopped and these systems are easy to use, readily adapted for automated injection and can operate at pressures up to 6000psi (41.4MPa) with reproducibility >0.2%. Six-port valves are commonly used, either fitted with an internal or an external sample loop and are an integral component of an HPLC system. 

So far, two principles of sampling have been applied in high-performance LC (HPLC) syringe and valve injection. Both types, conmercially available or custom-made, are discussed in detail below. 

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