Accurate Mass Fragment Library for Rapid Analysis of Pesticides on Produce Using Ambient Pressure Desorption Ionization with High-Resolution Mass Spectrometry

Abstract

U.S. food imports have been increasing steadily for decades, intensifying the need for a rapid and sensitive screening technique. A method has been developed that uses foam disks to sample the surface of incoming produce. This work provides complimentary information to the extensive amount of published pesticide fragmentation data collected using LCMS systems (Sack et al. Journal of Agricultural and Food Chemistry, 59, 6383-6411, 2011; Mol et al. Analytical and Bioanalytical Chemistry, 403, 2891-2908, 2012). The disks are directly analyzed using transmission-mode direct analysis in real time (DART) ambient pressure desorption ionization coupled to a high resolution accurate mass-mass spectrometer (HRAM-MS). In order to provide more certainty in the identification of the pesticides detected, a library of accurate mass fragments and isotopes of the protonated parent molecular ion (the [M+H]⁺) has been developed. The HRAM-MS is equipped with a quadrupole mass filter, providing the capability of "data-dependent" fragmentation, as opposed to "all -ion" fragmentation (where all of the ions enter a collision chamber and are fragmented at once). A temperature gradient for the DART helium stream and multiple collision energies were employed to detect and fragment 164 pesticides of varying chemical classes, sizes, and polarities. The accurate mass information of precursor ([M+H]⁺ ion) and fragment ions is essential in correctly identifying chemical contaminants on the surface of imported produce. Additionally, the inclusion of isotopes of the [M+H]⁺ in the database adds another metric to the confirmation process. The fragmentation data were collected using a Q-Exactive mass spectrometer and were added to a database used to process data collected with an Exactive mass spectrometer, an instrument that is more readily available for this screening application. The commodities investigated range from smooth-skinned produce such as apples to rougher surfaces like broccoli. The minimal sample preparation and absence of chromatography has shortened the analysis time to about 15 min per sample, and the simplicity and robustness of the technique make it ideal for rapid screening.

Applications of direct analysis in real time mass spectrometry in food analysis: A review

“…The applications of DART‐MS to fruits and vegetables have been broadly demonstrated. For instance, the rapid screening of pesticides on the surfaces of multiple fruits and vegetables (e.g., apples, grapes, oranges, peaches, kiwis, tomatoes, cherry tomatoes, and pears) by DART‐Orbitrap‐MS was reported, presenting very sensitive detection at the level of 2–10 ng/g on sample surfaces 19,25–29 . In these studies, the pesticides of interest at the levels of 10 and 100 times below the United States Environmental Protection Agency tolerances were detected with 3 ppm mass accuracy using the swabbing approach.…”

Applications of DART‐MS for food quality and safety assurance in food supply chain

“…Additionally, DART desorption temperatures less than 250°C were needed to avoid ionization induced by the polyester swab itself, and the utilization of temperature gradient of DART gas could attribute to the varying thermal desorption profiles of the analytes of interest. The incorporation of isotopes of the [M+H] + in the database could enhance the identification capability of pesticides (Edison, Lin, & Parrales, ; Edison et al, ; Crawford & Musselman, 2012; Kern, Lin, & Fricke, ).…”

“…Temperature gradient and ramping of DART gas temperature can be used for the optimization of source conditions. A temperature gradient can facilitate separation of the pesticides through varying thermal desorption profiles of the compounds of interest (Kern, Lin, & Fricke, 2014). Using temperature ramp technique, compounds having the same nominal mass can be thermally separated (Nilles, Connell, & Durst, 2010).…”

“…Multiple sample holders are positioned in-line between the DART source exit and the mass spectrometer inlet, and passed though by the helium gas stream in perpendicular direction to the axis. Fabrics, swabs/ disks, and filter paper have been successfully employed for certain applications, including antimalarial insecticide on mosquito netting (P erez et al, 2010) and fragrant galaxolide on fabric (Haefliger & Jeckelmann, 2007), multiple pesticide residues on fruit and vegetable surfaces by swabs/disks (Edison, Lin, & Parrales, 2011;Crawford & Musselman, 2012;Kern, Lin, & Fricke, 2014), and strobilurin fungicides in wheat by filter paper (Schurek et al, 2008). The auxiliary devices of TM or tweezers can hold the swabs/disks and fabrics for introducing analytes into MS inlet.…”

Quantitative profiling of perfluoroalkyl substances by ultrahigh-performance liquid chromatography and hybrid quadrupole time-of-flight mass spectrometry

“…The problem of target screening is that a number of related compounds remain undetected in the sample just because they were not selected a priori as the analyte [24]. The ability to obtain mass spectra with a very high degree of mass accuracy at sufficient mass resolutions and high sensitivity opens the possibility for combining both non-target and target quantification [26][27][28].…”