Agriculture Reference
In-Depth Information
Figure 2.15.
The impact of dispersive SPE cleanup employing PSA and MgSO
4
on deoxynivalenol
(DON) (
m
/
z
331.0943
±
4 ppm) signal intensity in wheat extract (spike 500
μ
g/kg). Given sorbent
amounts were used for 4ml of acetonitrile extract containing equivalent 800mg of matrix; solvent
standard concentration was 100 ng/ml Ref. [128], Figure 2, p. 1956. Reproduced with permission of
Elsevier Science Ltd.
separation, the impact of matrix effects in ambient MS is typically more severe. The
need for characterizing and preferably minimizing matrix effects is of high concern in
qualitative and quantitative food analyses of analytes occurring at low concentration
levels. In such applications, the use of some sample preparation steps that enable
discrimination of at least some sample matrix is practically unavoidable. Because
these procedures represent a bottleneck of the whole analytical work
ow, rapid and
simple protocols are typically followed [95,96]. The effect of matrix on signal
intensity was reported in studies concerned with both DART and DESI; in the latter
case, mainly for some pharmaceuticals, Kauppila et al. documented severe signal
suppression of dobutamine. Even if a diluted urine solution was analyzed, no signal of
the target analyte could be detected. Apparently, DESI ionization was obstructed by
the urine matrix [130]. To overcome signal suppression of pesticides in DESI-based
direct surface analysis of fruits, a sample surface extraction with acetonitrile and
analysis of dried extract were performed. The signal intensity was approximately half
of that observed in pure solvent [129]. Another strategy employing a modi
ed
QuEChERS procedure was used in the analysis of mycotoxins in cereals [128]. The
amount of sorbent (primary secondary amine, PSA and magnesium sulfate, MgSO
4
)
used in the dispersive SPE step of the crude acetonitrile extract was optimized for the
most effective cleanup (see Figure 2.15). A signal increase of 12
-
39% was achieved
for target analytes (100% intensity in pure solvent).
Quantification
DESI and DART are currently perceived mainly as qualitative tools.
However, several studies have documented that they can also be applied to semi-
quantitative or even quantitative analysis [95,96]. In quantitative applications, relatively
high signal
fluctuation in repeated analyses (as high as 50%), as well as matrix effects,
