Agriculture Reference
In-Depth Information
has to be overcome by using suitable internal standards (preferably isotope-labeled
analogs of the analyte). It should be noted that this typically applies only to the analysis of
liquid samples. Quanti
cation in solid samples is much more complicated or even
impossible due to uneven distribution of analytes and other problems related to
preparation of homogeneous standard material. Thorough validation, in-batch analysis
of quality control samples, and comparison of results with those of established methods
have to be performed to obtain reliable quantitation and demonstrate that the use of
ambient MS-based method is
fit for purpose.
A precision of 15% and linearity of 0.99 over two orders of magnitude were
reported by Garcia-Reyes et al. for DESI analysis of imazalil spiked into an orange
extract together with labeled
d
5
-imazalil (internal standard). The results were in
excellent agreement with those obtained using an LC
MS method. The authors noted
that such performance characteristics cannot be considered a standard practice in food
analysis and in most cases DESI is able to deliver only semiquantitative information
on analyte concentration level [117].
The capabilities of DART in quantitative analysis of food have been recently
demonstrated for melamine and cyanuric acid in milk powder [126], mycotox-
ins [128], some pesticides [131], and iso
-
avones (see Table 2.5) [132]. Without
exception, an internal standard had to be employed to obtain acceptable precision.
2.3.3.3 Applications of Ambient Desorption/Ionization Techniques
in High-Throughput Analysis of Food
An overview of selected applications of the above described ambient ionization
techniques in high-throughput food analysis is provided in Table 2.5.
Edison et al. described a surface swabbing technique coupled to TM-DART-
HRMS for the rapid screening of pesticide residues in fruits [138]. Rather than using a
C over 3min was used to
achieve a minimal separation of analytes based on volatility differences. Of the 132
pesticides involved in the study, 86% of target compounds could be consistently
detected at levels of 2 ng/g (per apple and orange) and 10 ng/g (per grape). The
identi
fixed ionization temperature, a gradient from 100 to 350
°
cation of analytes was performed based on accurate mass measurements
facilitated by the Orbitrap mass analyzer. The results of the procedure were found
to be comparable in terms of identi
cation of pesticides with those obtained by the
LC
MS method and greatly increased the sample throughput by reducing sample
preparation and analysis time.
ASAP-HRMS instrumentation was used in another study concerned with screen-
ing of strobilurin pesticides [94]. Direct detection of azoxystrobin in ground wheat
samples was possible by stirring the glass ASAP probe among the ground solid
sample and introducing it into the ASAP source. During analysis of blank and
contaminated wheat (
n
-
20 each) containing 0.3mg/kg of azoxystrobin, ASAP-MS
enabled detection of all positive samples at 95% con
=
dence interval.
An interesting application of noninvasive neutral desorption (ND) sampling and
EESI-MS was reported by Chen et al., who applied this technique to fruit maturity and
quality assessment [135]. The mass spectral
fingerprints obtained by EESI of bananas,
