Download 3 - Agilent Technologies

Abundance
6
4 5
3
12
0
7
8 1
2
3
4
5
6
7
8
Aldicarb sulfoxide
Aldicarb sulfone
Methomyl
3-hydroxycarbofuran
Aldicarb
Carbofuran
Carbaryl
Methiocarb
10 Time [min] 20
Figure 72
Carbamate analysis
and, as they shrink, analyte ions are desorbed. The ions
are transported to the mass analyzer through a series of
vacuum stages and ion-focusing elements.
Electrospray ionization can produce multiply charged ions
of macromolecular analytes such as proteins and peptides.
Because mass analyzers separate ions based on mass-tocharge ratio (m/z), lower-cost mass spectrometers with
mass ranges of several thousand m/z can be used to analyze
compounds in excess of 150,000 daltons. The primary use of
electrospray has been the analysis of compounds of higher
molecular weight. However, this technique also has been
applied successfully to small polar molecules. Fig. 72 shows
a separation of carbamate pesticides using electrospray.
HPLC inlet
Nebulizer
Skimmers
Octopole
Capillary
+
+
+
+
+
Corona
needle
Fragmentation
zone (CID)
Lenses
Quadrupole
Figure 73
APCI LC/MS interface
APCI also can be used to analyze moderate polarity
analytes. As in electrospray, APCI ionization occurs at
atmospheric pressure via a chemical ionization process
(see figure73).
103