Pneumatic injectors

A pneumatically driven syringe that repeatedly injects the solution into the NMR tube and draws it back into a reservoir located in the bore of the magnet, thus efficiently mixing depleted and fresh portions of the sample between scans, was successfully used in protein work. A much more sophisticated pneumatic injector with a dead time as low as a few tens of milliseconds has been described in Ref. 79 its performance was assessed using digital video measurements, rapid-acquisition NMR measurements following a pH jump, and NMR imaging. 

The sample is introduced into the ICP as a liquid which must usually contain less than 0.1% dissolved solids to prevent salt build-up on the nickel cones (see Section 5.3). This is in contrast to ICP-AES, which can tolerate up to 1% dissolved solids. The sample is converted to an aerosol by means of a pneumatic nebulizer, and the droplets pass through a spray chamber, into the injector tube of the quartz torch and thence into the central channel of the ICP. These processes are identical with those described for ICP-AES (see Section 4.4.3), and the different types of... 

Figure 3.5—The two positions of a loop injector, a) Load sample b) Inject sample. Schematic of the model 7125 valve from Rheodyne Inc. Injection valves can be manual, pneumatic or electrical (reproduced with...

Aminoplast is pneumatically transferred from bin (1) through a feeder and an injector to bin (2) provided with a cyclone separator and an agitator. 

Two types of injectors are frequently employed. For packed column SFC, a standard six port rotary valve with an external sample loop of 1-10 pL has proven to be quite reliable. For capillary column SFC, a similar rotary valve with an internal "loop of 0.2 to 0.5 pL is typically employed. Frequently the rotor is pneumatically actuated in a very rapid fashion to allow only a small fraction of sample to be introduced ("time-split ) this is done to avoid column overload. Alternatively, the flow from the injector is split off in the same fashion as in GC. A disadvantage of the latter mode is the potential for sample discrimination. 

Experimental (simplex and window diagram). The chromatographic system consisted of a Model 501 supercritical fluid chromatograph (Lee Scientific, Salt Lake City, Utah) with the flame ionization detector (FID) set at 375°C. The instrument was controlled with a Zenith AT computer. A pneumatically driven injector with a 200 nL or a 500 nL loop was used in conjunction with a splitter. Split ratios used were between 5 1 and 50 1, depending on sample concentration and the chosen linear velocity, while the timed injection duration ranged from 50 ms to 1 s. We found that the variation of both the split ratio and injection time allowed greater control over the... 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

As a rule, the molds are filled pneumatically. This can be accomplished with a blower centered over the filling injectors. The air blown in is removed through perforated walls, or through special devices. It is also possible to suck in the material by applying a vacuum in the mold. It is practical to add to the prefoamed material the foam accumulated during cutting, as reclaim rates up to 20% are possible without quality deterioration. 

FIGURE 32.13 Microfluidic multi-injector, (a) 3D schematic representation of the device shows two small-diameter channels under the control of microfluidic valves that pneumatically eject fluid into a cell culture reservoir to form soluble molecule gradients, (b) Top view of the device in operation forming gradients of fluorescein isothiocyanate (FITC)-conjugated dextran. (c) 3D plot of the fluorescence intensity within the cell culture reservoir. (Adapted from Chung, B. G., et al., Lab Chip, 6, 6, 764, 2006. Reproduced with permission from The Royal Society of Chemistry.)... 

The flow FFF systems are characterized by the use of a second pump to drive carrier across the channel thickness this setup provides the field that induces migration of sample toward the accumulation wall. The Flow I system was operated with an Isochrom EC pump (Spectra-Physics Inc., San Jose, CA) as the channel flow pump and a pulseless syringe pump (built in-house) as the cross-flow pump. Sample was injected via a Valeo injector (Valeo Instruments co., Houston, TX) with a 20-pL loop, and the eluted sample was detected at 254 nm with a UV-visible detector (UV-106, Linear Instruments, Reno, NV). The peripheral equipment employed in How II and ni consisted of a Kontron model 410 channel flow pump, a syringe pump serving as the cross-flow pump, a Rheodyne (Cotati, CA) model 7010 pneumatic-actuated injection valve, and a model 757 Spectroflow UV-vis detector from Applied Biosystems (Ramsey, NJ) operated at 254 nm. 

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