Gas Chromatography - Tandem Techniques - Gas Chromatography Mass Spectroscopy (GC-MS) Systems > The Ryhage Concentrator > Page 63

Gas Chromatography Mass Spectroscopy (GC-MS) Systems

Just four years after the first disclosure of GC as an effective separation technique by James and Martin in 1953, Holmes and Morrell, 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-flow 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 of vapor concentrating devices.

 

Vapor ConcentratorsA number of concentrating devices have been developed, e.g. the jet concentrator invented by Ryhage (17), and the helium diffuser developed by Bieman (18) later known as the Bieman concentrator.

 

The Ryhage Concentrator

 

A diagram of the Ryhage concentrator is shown in figure 51. The concentrator comprised an aligned series of jets separated from each other by accurately adjusted gaps (normally two jets were used but sometimes three or more were employed).