Agriculture Reference
In-Depth Information
separation of multiple analytes requires the proper selection of both chromatographic
columns and composition of mobile phases and a careful optimization of chromato-
graphic parameters such as temperature, mobile-phase gradient, pH, and composition
of buffers. In practice, chromatographic columns using RP-C
18
stationary phases are
almost universally applied. The most comprehensive multitarget LC
MS method
dealing with the analysis of 320 toxic and potentially toxic mycotoxins was developed
and published by Abia et al. [51]. This methodology amends methods published
previously by Sulyok et al. [48,54]. For the chromatographic separations used
here [51,53], an HPLC system employing an RP-C
18
column was used. For
suf
-
ciently sensitive analyses for all compounds, two separate chromatographic
runs had to be performed in positive (ESI(
)) electrospray
modes using a triple quadrupole linear ion trap (QLIT) MS instrument. The time
needed for LC
+
)) and negative (ESI(
MS analysis of all 320 analytes was 41min per sample. A similar
strategy was also employed in a study by Lacina et al. [24], who analyzed 38
mycotoxins together with 288 pesticides. This analysis was also subdivided into two
consecutive runs with run times of 15.5 min each. In a study by Mol et al. [29], two
20min UHPLC
-
MS/MS methods were applied for the determination of mycotoxins
and natural toxins (
n
-
86) in both
positive and negative ionization modes. Herrmann et al. [52] performed simultaneous
analysis of 36 mycotoxins together with some drugs, pesticides, and other chemical
contaminants, representing in total 127 target analytes. This analysis was again
subdivided into two separate runs. Each was accomplished within 22min and
resulted in a total analysis time of 44 min per sample. Two separate runs in ESI
(
=
36), pesticides (
n
=
136), and veterinary drugs (
n
=
) modes are commonly applied in multitarget analyses where triple
quadrupole (QqQ) or QLIT are used as mass analyzers. This is necessary because of
the high number of simultaneously eluted analytes that differ in terms of their optimal
ionization modes. Because the polarity switching is not rapid enough to enable
simultaneous acquisition in both ionization modes when employing common LR-MS
instruments, the only viable solution to achieve acceptable LODs is to separate the
analytes into positive and negative ionization mode runs. For example, a
+
) and ESI(
atoxins
(ionizing in ESI(
)), which represent highly
important regulated toxins, cannot be easily separated with C
18
columns and therefore
typically overlap or coelute.
The LC parameters of the above LC
+
)) and trichothecenes (ionizing in ESI(
-
MS methods were more or less similar. The
dimensions of
the most
frequently employed UHPLC columns were 100 or
150
×
2.1 mm with 1.7 or 1.8
μ
m particle sizes [24,29,53] or 150
×
4.6 mm with
5
m particle sizes for HPLC analysis [48,51]. In one case, a shorter column
(50
μ
×
2.1mm, with 1.8
μ
m particle sizes) was applied in UPLC
-
MS/MS analysis [52].
The column temperatures ranged from 25 to 55
°
C. The majority of methods
employed acidi
ed ammonium formate (1
-
5 mM) and acidi
ed methanol in ESI
(
) ionization mode for the mobile phase, while aqueous ammonium acetate (5 mM)
and methanol were used in ESI(
) mode.
Multianalyte methods developed speci
+
cally for the determination of mycotoxins
usually have quite similar parameters, as described in the above applications. These
were recently summarized in a review by Hajslova et al. [55]. The state-of-the-art
