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Multidimensional Electrodriven Separations 205

Figure 9.6 Surfer-generated chromatoeletropherogram of fluorescamine-labeled tryptic
digest of ovalbumin. Reprinted from Analytical Chemistry, 62, M. M. Bushey and J. W.
Jorgenson, ‘Automated instrumentation for comprehensive two-dimensional high-perfor-
mance liquid chromatography/capillary zone electrophoresis, pp 978–984, copyright 1990,
with permission from the American Chemical Society.

An example of the results obtained in the form of a “chromatoelectropherogram”
can be seen in Figure 9.6. The contour type data display showed the three variables
that were studied, namely chromatographic elution time, electrophoretic migration
time, and relative absorbance intensity. Peptides were cleanly resolved by using this
two-dimensional method. Neither method alone could have separated the analytes
under the same conditions. The most notable feature of this early system was that
(presumably) all of the sample components from the first dimension were analyzed
by the second dimension, which made this a truly comprehensive multidimensional
technique.
In 1993, Jorgenson’s group improved upon their earlier reverse phase
HPLC–CZE system. Instead of the six-port valve, they used an eight-port electri-
cally actuated valve that utilized two 10- L loops. While the effluent from the HPLC
column filled one loop, the contents of the other loop were injected onto the CZE
capillary. The entire effluent from the HPLC column was collected and sampled by
CZE, making this too a comprehensive technique, this time with enhanced resolving
power. Having the two-loop valve made it possible to overlap the CZE runs. The
total CZE run time was 15 s, with peaks occurring between 7.5 and 14.8 s. In order to
save separation space, an injection was made into the CZE capillary every 7.5s,