Pesticide analysis by pulsed flow modulation GCxGC-MS with Cold EI—an alternative to GC-MS-MS
We explored the use of pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GCxGC) mass spectrometry with supersonic molecular beams (SMB) (also named Cold electron ionization (EI)) for achieving universal pesticide analysis in agricultural products. The use of GCxGC serves as an alternative to MS-MS in the needed reduction of matrix interference while enabling full-scan MS operation for universal pesticide analysis with reduced number of false negatives. Matrix interference is further reduced with Cold EI in view of the enhancement of the molecular ions. Pulsed flow modulation is a simple GCxGC modulator that does not consume cryogenic gases while providing tuneable second GCxGC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. PFM-GCxGC-MS with Cold EI combines improved separation of GCxGC with Cold EI benefits of tailing-free ultra-fast ion source response time and enhanced molecular ions for the provision of increased sample identification information and reduced matrix interference. Consequently, PFM GCxGC-MS with Cold EI also improved NIST library identification probabilities of the spiked pesticides. PFM GCxGC is further characterized by largely increased second column sample and matrix capacity that as a result performs much better than thermal modulation GCxGC-MS with standard EI in the suppression of matrix interference. In a comparison with standard GC-MS, we measured with PFM GCxGC-MS with Cold EI an average total ion count matrix interference reduction factor of 32 for 12 pesticides in two matrices of baby leaves mixture and lettuce. In addition, Cold EI further increases the range of pesticides amenable for GC-MS analysis and its response is relatively uniform hence with it the need for pesticides specific calibration is reduced.
KeywordsPulsed flow modulation GCxGC GCxGC-MS Supersonic molecular beams Cold EI Pesticide analysis
This research was supported by the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities (grant No 356/15). This research was also supported by the Ministry of Science and Technology, Israel, and by the Pazi grant number 266/15 of the Israel Atomic Energy Commission.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
- 1.Turner JA. Pesticides manual. 17th edition. British Crop Protection Council; 2015.Google Scholar
- 2.Pesticide Manual Online. 2017. http://www.bcpc.org/product/bcpc-online-pesticide-manual-latest-version. Accessed 20 Mar 2017.
- 5.Ochiai N, Ieda T, Sasamoto K, Takazawa Y, Hashimoto S, Fushimi A, et al. Stir bar sorptive extraction and comprehensive two-dimensional gas chromatography coupled to high-resolution time-of-flight mass spectrometry for ultra-trace analysis of organochlorine pesticides in river water. J Chromatogr A. 2011;1218:6851–60.CrossRefGoogle Scholar
- 8.Hoh E, Lehotay SJ, Pangallo KC, Mastovska K, Ngo HL, Reddy CM, et al. Simultaneous quantitation of multiple classes of organohalogen compounds in fish oils with direct sample introduction comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry. J Agric Food Chem. 2009;57:2653–60.CrossRefGoogle Scholar
- 9.Hoh E, Lehotay SJ, Mastovska K, Ngo HL, Vetter W, Pangallo KC. Capabilities of direct sample introduction-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry to analyze organic Chemicals of Interest in fish oils. Environ Sci Technol. 2009;43:3240–7.CrossRefGoogle Scholar
- 10.Hoh E, Dodder NG, Lehotay SJ, Pangallo KC, Reddy CM, Maruya KA. Nontargeted comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry method and software for inventorying persistent and bioaccumulative contaminants in marine environments. Environ Sci Technol. 2012;46:8001–8.CrossRefGoogle Scholar
- 11.Fernandes VC, Lehotay SJ, Geis-Asteggiante L, Kwon H, Mol HGJ, van der Kamp H, et al. Analysis of pesticide residues in strawberries and soils by GC-MS/MS, LC-MS/MS and two dimensional GC-time-of-flight MS comparing organic and integrated pest management farming. Food Addit Contam Part A. 2014;31:262–70.CrossRefGoogle Scholar
- 14.Amirav A. Pulsed flow modulation gas chromatography mass spectrometry with supersonic molecular beams method and apparatus. Israel Patent application number 176724 (2006), USA Patent 7518103 submitted in 2007 issued 2009.Google Scholar
- 15.Keshet U, Fialkov AB, Alon T, Amirav A. A New pulsed flow modulation GC×GC–MS with Cold EI system and its application for jet fuel analysis. Chromatographia. 2016;79:741–54.Google Scholar
- 18.Phillips JB, Xu J. Comprehensive Multi-dimensional gas chromatography. J Chromatogr A. 1995;703:327–34.Google Scholar
- 21.Mondello L. Comprehensive chromatography in combination with mass spectrometry. Wiley; 2011.Google Scholar
- 22.Dutch mini-Luke extraction method “Analytical Methods for Pesticide Residues in Foodstuffs”, 6th edition. The Hague: Inspectorate for Health Protection, Ministry of Health, Welfare and Sports; 1996.Google Scholar
- 25.Alon T, Amirav A. How enhanced molecular ions in Cold EI improve compound identification by the NIST library. Rapid Commun Mass Spectrom. 2015;29:2287–92.Google Scholar