
Introducing the MSQ
The Source–An Introduction to API Techniques ________________________________________________
Table 1-2. Comparison of ESI and APCI
LC/MS technique
Electrospray (ESI)
Atmospheric Pressure Chemical
Ionization (APCI)
Compound polarity
Polar
Polar, some non-polar
Examples
Drugs, proteins, biopolymers,
oligonucleotides, steroids, and
pesticides
Pesticides, azo dyes, drugs,
metabolites, agrochemicals, and
steroids
Sensitivity
fg to pg (compound-dependent)
fg to pg (compound-dependent)
Type of spectra
[M+H]
+
for +ve ion mode, [M-H]
-
for
-ve ion mode, fragmentation via
source voltage
[M+H]
+
for +ve ion mode, [M-H]
-
for
-ve ion mode, fragmentation via
source voltage
Flow rates
2.0 µL/min to 2.0 mL/min
0.2 to 2.0 mL/min
LC columns
Capillary to 4.6-mm ID columns
2.1- to 4.6-mm ID columns
Mobile phases
H
2
O, CH
3
CN, CH
3
OH are most
frequently used.
H
2
O, CH
3
CN, CH
3
OH are most
frequently used. Non-polar
solvents can be used.
Typical mass range
<100,000
<1000
1-22
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