Page 377 - Tandem Techniques

Page 361

Figure 9.21
The Hewlett -Packard Electrospray Ionization LC/MS Interface
Courtesy of the Hewlett-Packard Company.

As already discussed, it is seen that the production of multiple charged ions, in effect, increases the
mass range of the spectrometer. As an example of the use of the ion spray LC/MS interface, the total
ion current chromatogram of a sample from the tryptic digest of lysozyme is shown in Figure 9.22. A
Vydac C-18 reversed phase column 250 mm long and 2.1 mm I.D. was used to separate the components
of the mixture, and was thermostatted at 50°C. The flow rate was 200 µl per min and the separation
was developed by gradient elution. The mobile phase composition was programmed from pure solvent
A (0.1% trifluoro-acetic acid (TFA) in water) to 60% solvent B (0.1% TFA in acetonitrile) over a
period of 60 minutes. The total column eluent was passed into the interface but, as seen from the
diagram of the interface and its mode of operation, only a portion of the solute actually enters the
interface. Furthermore, of that portion that does enter, only a fraction of it is carried into the mass
analyzer. The mass spectrometer employed was the Hewlett-Packard MS Engine Quadrupole Mass
Spectrometer. The mass spectrum of the peak eluted at 30.35 minutes is shown in Figure 9.23.