Mixed phase port

The mixed phases leaving the impellor are further stirred in the mixing chamber and then leave it by flowing between the baffles protecting the mixed phase port. These baffles are arranged to accept liquor from the pump with the minimum of by-passing , and rotation of the pump in the opposite direction is distinctly less satisfactory. 

Mixer and settler liquor levels. A difference in total liquor level exists between mixers and settlers so that the light phase can flow over a weir from a mixer. This can be deduced simply from the hydrostatic balance about the mixed phase port A between a mixer and its own settler. 

Settler interface levels. The interface level in the end stage where the dense phase leaves the extractor is simply controlled by means of a dense phase overflow weir. This is set at a suitable height to maintain the interface below the level of the mixed phase port. 

The type of stirrer used in a simple stirred mixer-settler is relatively unimportant provided it mixes the two phases adequately. It is clearly not necessary for it to have any pumping action. Neither is it essential for any individual stirrer to be operable at any particular time, since the effect of a breakdown in a single stage is merely to lose the extraction effect of that stage. An interface will form in the faulty mixing chamber at the level of the mixed phase port and both phases will take their normal paths, except without mixing. 

Tanner, M. C. In-line Mixer-Settler having Double Mixed Phase Ports. U.K. Patent Specification 835,282 (application 1957). 

Droplet generation (Fig. 3a) was performed using a flow-focusing technique (flow rate 1 pL/h for Ports A and B and 4 pL/h for the oil phase). Ports A and B were for the delivery of the amino acid mix and nucleic acid mix, respectively. The two reagent mixtures were merged prior to droplet formation. In this case, protein synthesis only occurred in the droplets. The high-throughput emulsion was then contained in a 400 pm wide reservoir. This reservoir allowed the droplets an incubation time of approximately... 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

The bottom of the mixing zone contains stationary vanes attached to the bottom of the contactor housing. These vanes stop the rotation of the dispersion that is created in the annular gap and allows the dispersion to flow under the rotor. The opening into the rotor is located at the center of the bottom surface of the rotor. If the bottom vanes were not there, the dispersion would back up in the annular mixing zone and flow out via the lower collector ring. If this happened, a breaking dispersion would flow out the less-dense-phase exit port. 

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. 

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