Agriculture Reference
In-Depth Information
2.2.1.2 Applications of Fast Gas Chromatography
-
Mass Spectrometry
Applications of fast GC approaches, such as the use of a column with a small internal
diameter, the use of a column with a thin
film of stationary phase, and low-pressure
GC combined typically with fast temperature programming, were evaluated by
several authors in the analysis of food and environmental contaminants (pesticide
residues [4,9,14
flame retardants [19,20], polycyclic aromatic
hydrocarbons [21], and polychlorinated biphenyls [22] as well as naturally occurring
food compounds (
-
18], brominated
(flavor compounds [23,24] and lipids underwent a transesteri
cation
in order to obtain the fatty acid methyl esters [25]).
In general, fast GC
MS has been demonstrated to increase the speed of analysis
for GC-amenable analytes in various foods and provide more advantages over
the traditional GC
-
-
MS approach,
including high sample throughput with,
in
most cases,
<
10min instrumental analysis time per sample (see an example in
Figure 2.1).
The bene
t of fast GC was further enhanced by rapid sample preparation. In
particular, the fast and inexpensive QuEChERS (quick, easy, cheap, effective, rugged,
and safe) extraction method [26] was employed for sample preparation in pesticide
residue analysis, which reduced the total time needed for the processing of samples by
a factor of
5 and the analysis time by a factor of
6 compared with
“
conventional
”
∼
∼
sample preparation approaches [9]. For the analysis of
flavor compounds, the use of
headspace solid-phase microextraction (HS-SPME) was shown to provide appropri-
ate sample preparation and preconcentration. This solvent-free, inexpensive sampling
technique enabled isolation of a wide range of analytes present in food crops and
products by their extraction from its headspace and concentration in the
ber
coating [27].
Regarding MS detection, the use of a single quadrupole MS operated in SIM
represented a limiting factor since only two to three ions could be monitored to obtain
acceptable detectability in (ultra)trace analysis [4,14]. In the case of a triple quadru-
pole MS operated in MRM, the initial identi
cation of pesticide residues was based on
MS/MS screening that monitored a single MS/MS transition (1 precursor ion
1
product ion) of each target compound followed by the repeated analysis of potentially
positive samples again using MS/MS to monitor two to three MS/MS transitions
(1 precursor ion
®
two to three product ions) for each compound [17]. The dis-
advantages of this approach were the need to optimize MS/MS conditions, reanalyze
the positive samples, and create many time segments in the method. However, with
the development of new instruments allowing accurate acquisition with very low
dwell times (1
®
-
5 ms), even two or more MS/MS transitions for
>
150 analytes with
analysis time
10 min were possible [16].
The number of analytes was not a limiting factor in studies using a time-of-
<
ight
(TOF) analyzer (either high-speed TOFMS (HSTOFMS) or high-resolution TOFMS
(HRTOFMS)) [11,15]. While the HSTOFMS instruments employed spectral decon-
volution of the acquired GC
MS records, the use of HRTOFMS allowed the unbiased
identification and reliable quantification of pesticide residues through the application
of a narrow mass window (0.02 Da) for extracting analyte ions and the availability
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