Chemistry Reference
In-Depth Information
Solvent 1A
Optional Solvent-
Select Valve
Solvent 1B
Pump 1
Outlet
Mixer
Pump 2
Solvent 2A
Optional Solvent-
Select Valve
Solvent 2B
(a)
Solvent A
Solvent B
Pump
Head
Outlet
Solvent C
Solvent D
µ-processor
(b)
FIgure 3.1
Diagram illustrating (a) high-pressure and (b) low-pressure mixing system
architecture. The high-pressure system uses two separate pumps and a controller; the low-
pressure system uses a single pump and a multiport proportioning valve.
for method and column screening approaches), and the mobile phases are often
more robust and accurate than premixed mobile phases when methods are in rou-
tine use. Figure 3.2 illustrates this capability. Figure 3.2c shows three overlaid chro-
matographic results from one system, three different chemists, on three different
days, using premixed solvents. The chemist-to-chemist reproducibility is seen to be
quite variable. In Figure 3.2b, every tenth injection of 100 runs from an experiment
using premixed solvents are overlaid. Figure 3.2b illustrates that even on a single
system, with a single chemist, premixing solvents can affect repeatability over time.
Variability in this instance most likely arises from selective evaporative loss of the
organic solvent, as later runs have longer retention times. Finally, in Figure 3.2a,
overlaid results are presented for every tenth injection of 100 runs using auto blend
or dial-a-mix; that is, using the system to make the mobile phase. As illustrated, the
