Page 316 - Tandem Techniques

Page 300

Figure 8.7
Detail of Stage and Concentric Flow Nebulizer
The total system is contained in an evacuated aluminum enclosure, which is fitted with windows to
observe the nebulization process. The enclosure is evacuated by means of a standard vacuum system,
fitted with a solvent trap to remove solvent vapor. The concentric flow nebulizer projects through the
upper plate and electrical connections are made through the plate to the nebulizer heater. The heater
consists of a few turns of chromel wire. Helium is fed into the column eluent, exterior to the deposition
chamber, and the total nebulizer assembly is shown in the upper part of Figure 8.8. Helium was chosen
as the nebulizing gas, as opposed to nitrogen, as helium has the higher thermal conductivity, and allows
greater heat transfer to the mobile phase. The average spot diameter of the solutes deposited on the disk
was reported as about 100 µm. The transport disk is shown in the lower half of Figure 8.8. The position
of the rotatable stage is adjusted by means of a micrometer screw, mounted beneath the stage, and
external to the vacuum chamber. The stage consists of a metal