High-pressure mixing system

A few years ago I would have always recommended the high-pressure mixing system, even though it was more expensive performance merited the difference in price. Today, it depends on the applications you anticipate running. If you plan on running 45-min gradients to separate 23 different components, some of them as minor amounts such as with PTH amino acids, then... 

My preference today would be for a high-pressure mixing system if I had to run very complex mixtures on a routine basis because these systems give the best reproducible gradients as a rule. As a routine research instrument or a methods development system, I would prefer a low-pressure, four-solvent dynamically mixed system using a dual-headed pump. I would use the deoxygenation apparatus (Fig. 6.4) to degas my solvents with helium and run them under a helium demand valve to conserve helium. 

Reduced dwell volume High-pressure mixing system, low-volume mixer... 

Figure 4.4. Schematic diagrams of a low-pressure mixing system (a) using a single pump and a four-port proportioning valve, and a high-pressure mixing system (b) using two separate pumps and a controller to blend solvents under high pressure.

Figure 2.6 High-pressure mixing systems use two or more independent pumps to generate the gradient. Low-pressure mixing systems use a singie pump with a proportioning vaive to controi composition. The advantages of high-...

Figures Schematic drawing of the high-pressure mixing system. (A) Inline mixer as normally used in HPLC systems. To provide the best mixing effect, the line with the buffer of higher density enters the mixer from the top while the less dense buffer is pumped in radially. (B) Inline mixer as normally used in a ProSys Workstation. Two mixers are connected together in series, separated by a seal with several bores. Both solutions are pumped radially into the first mixer and leave the system from the second (From Ref. 53.)...

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