Page 403 - Tandem Techniques

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Figure 9.43
Spectrum of a Product from the Tryptic Digest of
Human Growth Hormone Obtained from a Low
Dead Volume Atmospheric Ionization Interface
Courtesy of the Perkin Elmer SCIEX Corporation
Cai and Henion [37] used a complex combination of sampling techniques to assay LSD and its analogs
in urine. First, the authors employed affinity chromatography to extract the substances of interest from
the urine. The sample was then displaced from the affinity column and collected in a trap, from which
the materials of interest were then displaced onto an LC column for separation. The column eluent was
then passed through an atmospheric pressure ionization interface to the mass spectrometer. A diagram
of their apparatus is shown in Figure 9.44.

The analytical procedure was complicated. First the immuno-affinity column (a HiPac protein G
column, 3.3 mm x 2.1 mm packed with 30 µm particles) was equilibrated with the phosphate buffered
saline (PBS). Then 30 µl of PBS-diluted antibody solution (10% antibody-90% PBS) was injected onto
the column. Then, humane urine diluted with PBS (50% urine-50 % PBS) was pumped through the
protein G column, which was immediately flushed with PBS to remove the weakly bound impurities.
During this process, the trapping column (1.5 cm long, 1 mm I.D. packed with 5 µm, C18 particles) and
the LC column (15 cm long, 0.3 mm I.D., packed with 3 µm C18 particles) were equilibrated with the
mobile phase. The PBS was then pumped through the affinity column, and the trap,