Low-pressure mixing

The present system incorporates electronically activated valves to feed the solvents at a programmed composition into a single pump (Fig. 3.3a). This is accomplished using a low pressure mixing chamber located before the pump. 

Similarly, as the high-velocity steam enters the mixing chamber shown in Fig. 16.1, it produces an extremely low pressure. The gas flows from the jet suction nozzle and into the low-pressure mixing chamber. It is not correct to say that the gas is entrained by the steam. The gas just flows into the mixing chamber, because there is a very low pressure in the mixing chamber. 

The Type II system comes in two flavors. They vary by the type of gradient pumping system they contain low-pressure mixing or high-pressure mixing. The rest of the system is the same injector, variable detector, and computer-based data acquisition and control. Autosamplers would allow 24-hr operation, but most university research laboratories find graduate students to be less expensive. 

Purge pump A with water and pump B with methanol. Dial-a-mix 20% B and equilibrate the column at 1.5mL/min (six column volumes or a stable baseline at 254 nm, about 10 min). (Lab note If the gradient system is a low-pressure mixing system, solvents must be degassed by purging or running under helium.)... 

High Pressure Figure 3.12 Low-pressure mixing system. 

Figure 4.2. Examples of modular and integrated HPLC systems. Modular systems (a) Agilent 1100 Series, (b) Jasco low-pressure mixing system. Integrated systems (c) Waters Alliance, (d) Shimadzu 2010.

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