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212 Multidimensional Chromatography

spectrometric detection was designed by Jorgenson and co-workers in 1997. In the
coupling of the CZE capillary to the MS detector, a new microelectrospray needle
was developed. Figure 9.12 shows a diagram of the silica sheath electrospray needle
specially designed for this instrument. This needle produced high ionization effi-
ciency, low flow rates, and a sheath flow that enabled the CZE to operate near opti-
mal conditions. A transverse flow gating interface was again used to couple the
reverse phase HPLC column to the CZE column. The result of this separation system
was the combination of the resolving power of reverse phase HPLC and CZE, with
mass spectrometric detection, all within 15 min (28).

9.14 THE FUTURE OF MULTIDIMENSIONAL
ELECTROKINETIC SEPARATIONS

Electrodriven separation techniques are destined to be included in many future mul-
tidimensional systems, as CE is increasingly accepted in the analytical laboratory.
The combination of LC and CE should become easier as vendors work towards pro-
viding enhanced microscale pumps, injectors, and detectors (18). Detection is often
a problem in capillary techniques due to the short path length that is inherent in the
capillary. The work by Jorgenson’s group mainly involved fluorescence detection to
overcome this limit in the sensitivity of detection, although UV–VIS would be less
restrictive in the types of analytes detected. Increasingly sensitive detectors of many
types will make the use of all kinds of capillary electrophoretic techniques more
popular.
Data analysis is one aspect of multidimensional analyses that must be optimized
in the future. The analysis of chromatographic data beyond one dimension is still
exceedingly problematic, especially in the analyses of highly complex mixtures.
Better software may need to be developed in order to analyze two- and three-dimen-
sional peaks due to their complexity. Three-dimensional data is only useful today in
terms of fingerprinting and often that even requires extensive data analysis. A great
deal of research must still be carried out to make the interpretation and quantification
of multidimensional data easier.

Figure 9.12 Schematic diagram of the silica sheath electrospray needle used to interface
capillary zone electrophoresis with a mass spectrometer.