Page 182 - Tandem Techniques

Page 165

Chapter 5
Gas Chromatography/Mass Spectroscopy (GC/MS) Tandem Systems

Just four years after the first disclosure of GC as an effective separation technique by James and Martin
in 1953, Holmes and Morrell [1], successfully combined the gas chromatograph with the mass
spectrometer to produce the first tandem system. The authors connected the column outlet directly to
the mass spectrometer employing a split system. The mass spectrometer was a natural choice for the
first combination instrument, as it could easily accept samples presented as a vapor in a permanent gas.
Prior to 1960, only packed GC columns were commercially available, and thus the major problem
encountered, when associating a gas chromatograph with a mass spectrometer, was the elimination of
the carrier gas. This was due to the relatively high flow rates that need to be used with packed columns
(ca 25 ml/min or more). The contemporary vacuum pumps at that time had relatively low pumping rates
(measured at atmospheric pressure), and thus only a small proportion of the eluate could be passed to
the mass spectrometer, which resulted in a significant loss of sensitivity. This problem was solved by
the use vapor concentrating devices.

Vapor Concentrators

In order to accommodate the relatively large flow rates that were used with packed GC columns, a
number of concentrating devices were