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eluent, the next coaxial tube carried the reagent, and the outside coaxial tube provided nitrogen to assist
the nebulization. The post-column addition of metallic chlorides to an eluent carrying carbohydrates
provides greater sensitivity, and assists in structural analysis. The relative abundance of protonated
carbohydrate and the metal complexes with lithium, sodium, potassium, rubidium and cesium are
different for each metal. Complexes with alkali metals significantly increase the sensitivity of the
system to the carbohydrate, and reflects the enhanced ionization in the electrospray interface by the
presence of the complexing reagents.

Figure 9.34
The Separation of Four Oligosaccharides
Using Metal Chloride Post-column Reagents
Reprinted with permission from M. Kohler and J. A. Leary,
67(19)(1995)3508, Copyright 1995 American Chemical Society.

It was shown that the lithium complex is over seventy times more abundant than the protonated species.
Although the lithium complex appears to provide the maximum sensitivity of the group examined, it
was also shown that cobalt complexes provided even greater sensitivity enhancement. Employing the
tri-axial electrospray with cobalt chloride as the complexing reagent, the chromatogram of 1 nmol of a
mixture of different carbohydrates, produced by single ion monitoring, is shown in