2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
Several extraction solvents including MeCn, methanol
(MeOH) and their mixtures with water were tested to achieve
good recovery for a wide range of analyte polarities. MeOH
and its mixtures with water offered good extraction efficiency
for polar and semi-polar compounds, however high amount
of matrix was also co extracted. Only aqueous MeCn was
used, because of poor extraction of polar analytes by pure
solvent. It is a common practice in many multi-mycotoxin
methods to employ azeotropic mixture of 84 % MeCn and
16 % water. This approach was developed for easy purification
by Mycosep and subsequently solvent evaporation,
nevertheless omitting purification step enabled improvement
of extraction efficiency of polar compounds (such as DOn-
3-glucoside, acephate, propamocarb) by increasing of water
content in extraction mixture up to 25 % (v/v). At the same
time, acceptable recoveries were still obtained for relatively
non-polar analytes represented e.g. by zearalenon and pyrethroid
insecticides.
It should be noted that the addition of water prior to
extraction into low moisture samples as cereals is also recommended
by a document n° SAnCO/2007/3131. To improve
recovery of fumonisin mycotoxins and protect unstable basesensitive
pesticides against the hydrolysis, addition of 1 % of
formic acid into extract mixture was necessary.
The final extract was diluted by water to decrease content
of MeCn and consequently to reduce matrix effects.
Different ratios of MeCn and water in a vial were tested,
nevertheless the content of water higher than 50% caused
precipitation of matrix components and consequently decreasing
of recovery of non-polar analytes.
O p t i m i z a t i o n o f L C - M S - M S
As mentioned above, no purification step was employed,
so chromatographic separation plays an important role to
separate analytes and matrix to decrease matrix effects.
Although slow gradient was used, very strong signal suppression
(over 80 % lower signal of matrix matched standard as
compared to solvent standard) still occurred for some of later
eluting compounds.
Many LC-MS pesticide multi-residues method use only
ESI + ionization, because almost of analytes ionize only in
positive mode or better sensitivity/selectivity is achieved
under these conditions. Although B-trichothecenes offer better
sensitivity in a negative mode by formation adducts with
acetic or formic anion (depends on composition of mobile
phase), ionization in positive mode is also possible. The main
advantage of positive mode is a compatibility with more than
95 % pesticides and other mycotoxins (aflatoxins, fumonisins)
which do not give any ions in ESI – .
M e t h o d V a l i d a t i o n
The distribution of recoveries of all analytes in wheat is
showen in Fig. 1. The recovery and repeatability of particular
analyte was obtained from analysis of spiked wheat material
at 100 μg kg –1 . The extraction method offers a good recovery
for both, acids and bases and covered a wide range of pola-
s405
rities. The trueness of method was demonstrated by analysis
of reference materials for mycotoxins (ochratoxin A, deoxynivalenol,
nivalenol, T-2 and HT-2 toxins) and proficiency
testing materials obtained from FAPAS 0950 and EUPT-C1/
SRM2. For all reference materials and positive findings in
proficiency tests were achieved satisfactory score |z| < 2.
Fig. 1. Distribution of recoveries of all 222 pesticide residues
and mycotoxins at concentration level 100 μg kg –1 in wheat
Conclusions
The multi-toxin LC-MS-MS method for simultaneous
analysis of 200 pesticide residues and 22 mycotoxins in
cereals has been developed and fully validated. Acceptable
recoveries and repeatabilities have been achieved for most
of analytes. The trueness of generated data was also documented.
The authors are convinced that this high throughput
approach will find a wide use in many control laboratories in
close future.
This study was carried out with support from the Ministry
of Education, Youth and Sports, Czech Republic from the
project MSM 6046137305 and partly from the project NAZV
1B53043 supported by the Ministry of Agriculture, Czech
Republic.
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