Environmental Engineering Reference
In-Depth Information
(a) GC-MS
Sample
Ion source
Oven
Mass filter
- - -
Column
+ + +
Detector
Interface
Control &
readout
GC
Gas
Vacuum system
(b) LC-MS
Sample
Interface/Ion source
Mass filter
- - -
Column
HPLC
Solvent
Detector
+ + +
Flow splitter
Control &
readout
Vacuum system
Figure 12.3
Diagram of two molecular mass spectrometers: GC-MS and LC-MS
and mass analyzers commercially available, but we will briefly introduce the most
commonly used ion sources in GC-MS and LC-MS. For mass analyzers, since
quadrupole (Section 12.1.1) is still the most widely used system in research and
commercial labs, we will no longer discuss other mass spectrometers. The readers,
however, should be aware of other mass analyzers for certain applications, such as
magnetic sector mass filter, time-of-flight (TOF) mass analyzer, and ion trap mass
analyzer. Magnetic sector systems, termed high resolution mass spectrometry, have
the major advantage of accurate molecular weight determination, but with
limitations of cost, size, and weight of permanent magnet. Time-of-flight mass
spectrometers have some general applications for volatile compounds but show
growing uses in LC/MS for large molecules such as proteins and DNA restriction
fragments. Another type of mass spectrometry that has become an extremely
powerful tool in many research labs is the tandem mass spectrometry (MS-MS), for
example, a triple quadrupole system consisting of three sets of quadrupole rods in
series. The triple quadrupole systems are the ideal research tools for determining
structures of primary molecular fragments.
Interface of GC-MS and LC-MS
Each hyphenated mass spectrometer is unique in the interface, coupling two
instruments and the method of ionization. The interface between ICP and quadruple-
based MS has been discussed. The interface between GC and MS is relatively
simple. GC equipment can be directly interfaced with rapid-scan mass spectrometers
with a proper flow adjustment. For capillary columns, the flow rate is usually small
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