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(c)
(b)
(a)
FIgure 3.2
Comparison of premixing mobile phase solvents to auto blend. Figure 1c:
three overlaid chromatographic results from one system, three different chemists, on three
different days, using premixed solvents. In Figure 1b, every tenth injection of 100 runs from
an experiment using premixed solvents are overlaid. In Figure 1a, overlaid results are pre-
sented for every tenth injection of 100 runs using auto blend, or dial-a-mix; that is, using
the system to make the mobile phase. (Reprinted from HPLC method development for phar-
maceuticals, Volume 8 of
Separation Science and Technology
, S. Ahuja, Editor, Chapter 6,
Contemporary liquid chromatographic systems for method development, p. 148, 2007.)
system is far more accurate in preparing the mobile phases than either a single or
multiple analysts premixing the mobile phase. Using auto blend, different organic
solvent proportions, buffer strength, and pH can be generated using the solvent man-
ager to proportionally mix the appropriate stock solutions to obtain the final mobile
phase conditions. Auto blending of this type can be used to the analyst's advantage
during method development.
The automated blending of solvents might at first seem a trivial matter. However,
automated method development systems depend on precise and reproducible blend-
ing in scouting experiments designed to study the effects of different mobile phase
conditions on selectivity. In the strictest sense, gradient chromatography is essen-
tially auto blending, albeit over time. The kinds of results obtained in Figure 3.2c
