Page 402 - Tandem Techniques

Page 386

A recent modification of the atmospheric pressure ionization technique, involving a special low dead
volume interface for use with microboe columns The packed microbore columns, (170 µm, 320 µm,
and 500 µm I.D., with lengths ranging from 5 to 15 cm) were used in conjunction with a low-volume,
wall-coated capillary column as an interface. The total ion current chromatogram of a tryptic digest
sample, comprising 1 picomole of human growth hormone, is shown in Figure 9.42. The column was
packed with an octadecyl bonded phase, having a mean pore size of 300 A, and a particle diameter of 7
µm. A gradient was employed which extended from 20% solvent (A), (0.1% TFA in water) to 80%
solvent (B) (75% 0.1% TFA in water and 25% acetonitrile) over a period of about 1 hour. Flow rates of
about 80 to 100 µl per minute were used, with about 3 µl passing to the capillary column and entering
the interface.

Figure 9.42
Total Ion Current Chromatogram of a Tryptic
Digest Sample of Human Growth Hormone
Courtesy of the Perkin Elmer SCIEX Corporation

It is seen that an excellent separation is obtained and apparently little resolution is lost in the capillary
interface. The mass spectrum of the peak marked T2 in the chromatogram is shown in Figure 9.43. It is
clear that good quality spectra can be obtained up to ion masses of at least 900. Such a combination of
techniques can be invaluable for the structure elucidation of compounds generated in biochemical
research.