Agriculture Reference
In-Depth Information
which highly complex samples such as foods are to be analyzed. The aim of the
following section is to address the key factors affecting the performance of ambient
MS-based methods employing DESI and DART techniques. In addition to optimiza-
tion of parameters directly related to ambient ionization, requirements on mass
spectrometric detection and sample preparation for both qualitative and quantitative
high-throughput analyses are brie
y discussed.
DESI Source Parameters
As mentioned above, a remarkably high number of
parameters affect the performance of DESI-based analytical work
ow. These param-
eters can be classi
ed as follows [97]:
Geometric parameters (incident angle
α
, collection angle
β
,
tip-to-surface
distance
d
1
, and MS inlet-to-surface distance
d
2
).
Spray parameters (spray capillary voltage, nebulizer gas pressure, and solvent
ow rate).
Chemical parameters (composition of sprayed solvent).
Surface parameters (potential, composition, and temperature).
practices and settings, which represent a good
start for DESI optimization in particular applications, are already available in the
literature. Some of these useful settings are provided in Table 2.4.
The geometric setup in DESI signi
Fortunately, some
“
gold standard
”
cantly affects the sensitivity of measurements.
The
α
and
d
1
parameters directly affect the ionization process and their optimal values
Table 2.4. The Overview of Typical Parameter Settings
in DESI and DART Experiments [91,95-97,115]
Parameter
Setting range
DESI
Incident angle (
α
)
30-70
°
Collection angle (
β
)
5-30
°
Tip-to-surface distance (
d
1
)
1-10mm
MS inlet-to-surface distance (
d
2
)
1-5mm
2-6kV
a
Spray capillary voltage
Nebulizer gas pressure
8-12 bar
Solvent flow rate
2-5
μ
l/min
DART
Ion source exit-to-MS inlet distance
5-25mm
Ionization gas temperature
150-450
°
C
Ionization gas
ow
0.5-3.5 l/min
Discharge needle voltage
1-5kV
150-350 V
a
Perforated electrode voltage
150 V
a
Grid electrode voltage
50
-
a
Voltages represent either positive or negative potentials, depending
on the ionization mode used.
