Page 184 - Tandem Techniques

Page 167

device was produced commercially and used extensively for packed columns with GC/MS tandem
systems, until they was eventually replaced by the open tubular column. Even today, the Ryhage
concentrator is often still often used in GC/MS systems when packed columns are employed.

The Bieman Concentrator

The Bieman concentrator was developed at about the same time as the Ryhage concentrator and, due to
its simplicity, was equally popular for use in GC/MS systems. A diagram of the Bieman concentrator is
shown in Figure 5.2 and, as seen, functions on quite a different principle. The concentrator consists of a
heated glass jacket surrounding a sintered glass tube. The eluent from the chromatograph passes directly
through the sintered glass tube and the helium diffuses radially through the porous walls and is
continuously pumped away. The helium stream enriched with solute vapor passes on to the mass
spectrometer.

Figure 5.2
The Bieman Concentrator

Solute concentration and sample recovery is similar to the Ryhage device but the apparatus, though a
little more bulky, is somewhat easier to operate. An alternative system was also devised, based on the
same principle, that employed a length of porous polytetrafluorethylene (PTFE) tube as the
concentrator, as opposed to a sintered glass tube; in other aspects the PTFE device functioned in the
same manner.

The development of the open tubular columns eliminated much of the need for concentrating devices,
as the mass spectrometer pumping system could easily dispense with the usual carrier gas flows that are
employed with