1. Acknowledgements:
A special thanks to Dr. Michelle Ward, Dr. Rena Robinson, Christina King,
Liqing Gu, Yaphet Geadion, Lindsay Osentoski, and the company sponsors who
made this session possible.
References:
(1) Garcia-Reyes, Juan, Ayanna Jackson, Antonio Molina-Diaz, and R. Cooks. "Desorption Electrospray
Ionization Mass Spectrometry for Trace Analysis of Agrochemicals on Food." American Chemical Society 81.2
(2008): 820-29. Analytical Chemistry. ACS. Web. 27 Sept. 2015.
<http://pubs.acs.org/doi/pdf/10.1021/ac802166v>.
(2) http://webbook.nist.gov/chemistry/
(3) http://www.chm.bris.ac.uk/ms/theory/esi-ionisation.html
Background
• An ESI-MS determines the mass-to-charge ratio by pumping the
sample solution through the capillary needle which results in the
charged spray of fine droplets. The resulting gaseous ions are
analyzed by the detector.
Experimental Design
Discussion
Conclusion
• The data could have been better quantified if an
internal standard was used and the ESI-MS
was coupled with the LC-MS.
• Further studies can be completed by analyzing
different pesticides, produce, and instrument
schemes.
• Some sources of error could have resulted in
the analyte concentrations being lower than
their LOD.
Introduction
• The purpose of this experiment was to detect
trace amounts of various insecticides and
fungicides on different types of produce since
the presence of these chemicals and their
degradation products could cause potential
health hazards1.
• An Electrospray Ionization mass spectrometer
was used for the identification of the various
agrochemicals in both the standard and
produce samples.
Figure 2: Ions were produced by applying a
voltage to the sample and an aerosol was created.
Figure 1: ESI MS used direct infusion with LTQ
ion trap with Finnigan Ion Max API source.
The Thermo Finnigan LTQ MS was used with the
following parameters: ESI+ Mode, Nitrogen Gas,
Full Scan Mode, 500 Scans, 150-2000 m/z range.
15 g of
homogenized
subsample
15 mL ACN
Shake 1 min
6 g MgSO4
1.5 g NaCl
Shake 20 sec
Centrifuge
3.7K rpm for
1 min
750 mg
MgSO4
150 mg PSA
Shake 20 sec
Centrifuge
3.7K rpm for
1 min
1 g of sample
in 100% ACN
Results
Analyte
202.0
(m/z)
293.1
(m/z)
297.1
(m/z)
306.2
(m/z)
404.1
(m/z)
Kale
(ppb)
0.9507 0.3415 2.2782 0.4711 0.0000
Apple
(ppb)
0.6342 0.0000 3.6492 0.6703 11.6670
Organic
Apple
(ppb)
0.4037 0.0000 7.8169 0.0000 2.8863
Spinach
(ppb)
4.0446 0.2367 2.3677 3.5713 2.4787
Organic
Spinach
(ppb)
0.0000 0.0000 0.0000 0.0000 0.0000
Orange
(ppb)
0.6282 0.0000 0.7045 0.0000 0.9824
Orange
Peel
2.4974 0.2825 2.6197 0.0000 11.8972
LOD
(ppb)
15.0000 2.0000 4.0000 5.0000 8.0000
Figure 3: Schematic of the Linear Ion Trap
Detector that was used to analyze the ions.
Figure 4: Mass Spec of Thiabendazole Standard, 199 – 208 m/z.
Figure 4: ESI-MS Spectra for orange and orange
peel samples, 195-415 m/z.
Figure 5: Identification of Thiabendazole in
orange and orange peel samples, 201.8-202.8 m/z.