Instant Notes: Analytical Chemistry

and is removed by pumps, while the larger sample molecules continue through

into the MS. A complete GC-MS system is shown in Figure 1(a). The interface

should be maintained at the temperature of the GC outlet, usually by enclosing

it in the GC oven.

Most types of mass spectrometer are suitable for GC-MS work, although

those with a quadrupole analyzer (Topic E14) are very often used because of

their ability to scan rapidly.

The chromatogram will be recorded by the GC detector and data system, but

can also be derived by continuously measuring the total ion current (TIC)for

the ions generated as a function of the elapsed time. This total ion current

chromatogram matches that from the GC detector, and may also detect other

solutes. By selecting a particular mass/charge (m/z) ratio, selected ion moni-

toring (SIM) may be used to detect a particular ion; for example, m/z320, 322

and 324 may be studied in analyzing mixed dioxins, since these ions are charac-

teristic of a particular tetrachlorodibenzo-p-dioxin. Detection down to 10–15g of

a solute is possible.

Applications Both qualitative and quantitative analysis can be achieved with GC-MS and it is
now used widely on complex samples of all types.

F3 – Gas chromatography-mass spectrometry 295

Carrier

gas

Sample

Gas

chromatograph

Splitter

Eluent

Optional

Chromatography

detector

VDU/computing

integrator

Interface Spectrometer

Spectra

stored on

computer

Chromatogram

generated from

spectral signals

printer

(a)

Fig. 1. (a) Schematic of a GC-MS system; (b) jet separator. Reproduced from F.W. Fifield

& D. Kealey, Principles and Practice of Analytical Chemistry, 5th edn, 2000, with permission

from Blackwell Science Ltd.

From GC To ion source

To vacuum

(b) To vacuum