Identification of imidacloprid metabolites in onion (Allium cepa L.) using high-resolution mass spectrometry and accurate mass tools.
BACKGROUND
Imidacloprid is a potent and widely used insecticide on vegetable crops, such as onion (Allium cepa L.). Because of possible toxicity to beneficial insects, imidacloprid and several metabolites have raised safety concerns for pollenating insects, such as honey bees. Thus, imidacloprid metabolites continue to be an important subject for new methods that better understand its dissipation and fate in plants, such as onions.


METHODS
One month after a single addition of imidacloprid to soil containing onion plants, imidacloprid and its metabolites were extracted from pulverized onion with a methanol/water-buffer mixture and analyzed by liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/QTOF-MS) using a labeled imidacloprid internal standard and tandem mass spectrometric (MS/MS) analysis.


RESULTS
Accurate mass tools were developed and applied to detect seven new metabolites of imidacloprid with the goal to better understand its fate in onion. The accurate mass tools include: database searching, diagnostic ions, chlorine mass filters, Mass Profiler software, and manual use of metabolic analogy. The new metabolites discovered included an amine reduction product (m/z 226.0854), and its methylated analogue (m/z 240.1010), and five other metabolites, all of unknown toxicity to insects.


CONCLUSIONS
The accurate mass tools were combined with LC/QTOF-MS and were able to detect both known and new metabolites of imidacloprid using fragmentation studies of both parent and labeled standards. New metabolites and their structures were inferred from these MS/MS studies with accurate mass, which makes it possible to better understand imidacloprid metabolism in onion as well as new metabolite targets for toxicity studies.
Department of Environmental Engineering, Center for Environmental Mass Spectrometry, University of Colorado, Boulder, CO 80309, USA. mthurman@ono.com
E Michael
EM
Thurman
Imma
I
Ferrer
Paul
P
Zavitsanos
Jerry A
JA
Zweigenbaum
D007093:Imidazoles / Q000737:chemistry* / Q000378:metabolism*; D007306:Insecticides / Q000737:chemistry* / Q000378:metabolism*; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D015394:Molecular Structure; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000737:chemistry* / Q000378:metabolism*; D019697:Onions / Q000737:chemistry* / Q000378:metabolism
D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; C082359:imidacloprid