Page 517 - Tandem Techniques

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(pore diameter 5 µm) by sintering. The tubes were then slurry packed with 1.5 µm particles of reversed
phase, and the column terminated with another silica gel frit. The supplementary pressure, applied by
the pump to the column during operation, was about 2250 psi.

Figure 13.14
Selected Ion (m/z, 714,7129) Chromatogram of a Peptide Separation
Reprinted with permission from K. Schmeer, B. Behhnke
and E. Bayer, Anal. Chem., 67(20)(1995)3656,
Copyright 1995 American Chemical Society

To avoid bubble formation from resistive heating, the concentration of TFA in the mobile phase was
kept to 0.07 ml/I, and the mobile phase consisted of a mixture of 40% acetonitrile and 60% TFA
solution in water. The applied potential gradient, used to produce electro-osmotic flow, was the
difference between the overall potential 25 kV and that of the electrospray potential 4.8 kV, which was
equivalent to about 20 kV. The accompanying electro-osmotic current was 0.8 µA. The concentration
of the solutes in the sample placed on the column was about 20 µg/ml. The high selectivity and
separating power of the technique is demonstrated by the separation of the enkephalin methyl ester and
the enkephalin amide shown in Figure 13.14. It must pointed out, however, that the selectivity of the
separation was enhanced by the inevitable accompanying