LAA-A-LM-E89 Liquid Chromatography Mass Spectrometry LCMS C8 Highly Polar Pesticide Multi-Residue Analysis in Food Safety by LC-MS/MS David R. Baker, Eric Capodanno, Mikaël Levi Shimadzu Corporation, UK; Phytocontrol, France; Shimadzu France, France Abstract The analysis of highly polar pesticides by a single LC-MS/MS method is extremely challenging as a consequence of diverse separation and detection behaviour. Conventional approaches in highly polar pesticide analysis often use single residue methods or small group specific methods which are time consuming and limit throughput. In this study, the panel of target analytes selected for analysis included a series of compounds that are typically addressed by multiple methods and workflows; glufosinate, glyphosate, ethephon, fosethyl aluminium, maleic hydrazide, perchlorate, ETU, PTU, nicotine, amitrole, chlormequat, daminozide, diquat, kasugamycine, mepiquat, paraquat and trimesium. To accelerate turnaround times and increase sample sizes for more complete testing programs two LC-MS/MS methods were developed for the measurement of a range of highly polar pesticides in their underivitised state using the LCMS-8 triple quadrupole mass spectrometer. All target compounds were quantified at. mg/kg which is below the European Union maximum residue limit for all studied compounds delivering a measurable impact on sample cycle time and productivity. Keywords: Highly polar pesticides, LCMS-8, food safety, glyphosate, diquat, paraquat, perchlorate Introduction The use of pesticides in the environment is constantly under review and in recent years regulatory bodies have adopted a hazards-based approach to pesticide regulation leading to an increased use of highly polar pesticides which present lower persistence and toxicity. Enforcing pesticide limits within regulatory limits defined as the maximum residue levels (MRL s; the maximum concentration of pesticide residues permitted in food and feed) requires methods that provide results quickly and accurately for a broad spectrum of chemical structures in a diverse range of food samples. Pesticide residue monitoring laboratories utilise multi-residue LC-MS/MS methods for the quantification of an ever increasing list of target pesticides. However, the measurement of highly polar pesticides by a single LC-MS/MS method is extremely challenging as a consequence of diverse separation and detection behaviour. For this reason, single residue methods or small group specific methods are often utilised to analyse these compounds, in some cases including the use of pre- or postcolumn derivatisation. Therefore, there is a clear need to reduce the number of separation methods applied to the analysis of highly polar pesticides to help accelerate sample throughput, reduce the cost platform, simplify analytical workflows and enhance data quality for regulatory reporting limits. Glyphosate Perchlorate Trimesium Diqaut Kasugamycine H C P H Cl H H Chlormeqaut CH + CH CH C H - Cl H C Paraquat CH S + CH - Cl + + CH Cl - + + ETU H H S H H H C H H H H H H H Glufosinate Mepiquat Maleic hydrazide icotine Amitrole H C P H H H + H C CH H H H C H H H C PTU H S H Fosethyl aluminium CH HP Al + - Figure. Target analyte structures
C8 The highly polar pesticides targeted in this study included glufosinate, glyphosate, ethephon, fosethyl aluminium, maleic hydrazide, perchlorate, ETU, PTU, nicotine, amitrole, chlormequat, daminozide, diquat, kasugamycine, mepiquat, paraquat and trimesium. Structures for these compounds are displayed in Figure. All of the compounds included in this study were polar, characterised with LogKow <. The most polar compounds being the cationic quaternary ammonium herbicides diquat (LogKow -.6) and paraquat (LogKow -.). Several of the compounds also have a low molecular mass, for example trimesium (77 g/mol), amitrole (8 g/mol) and ETU ( g/mol). The analysis of highly polar pesticides is extensively reported in literature but the methods have been limited to a small number of specific target compounds and not to a group with such a diverse chemical space. For example, a common approach for the analysis of one of the world s biggest selling herbicides glyphosate is typically achieved by FMC derivatization. This derivatization step is specific for glyphosate, glufosinate and AMPA residues in water and food samples but it is relatively complex, limits throughput and repeatability and reproducibility can suffer due to the derivatisation step. The aim of this study was to develop a fast, sensitive and simple methodology for a range of challenging highly polar pesticides that require single-residue methods, by as few multiresidue LC-MS/MS runs as possible and without the need for derivatisation. Several different analytical columns and mobile phases were evaluated in this study, in addition to assessing the MS/MS parameters. Isotopically labelled standards were used to compensate for matrix effects. Initial data was collected in food matrix using a triple quadrupole mass spectrometer in MRM mode. Experimental Individual reference standards for each compound were provided by Phytocontrol in methanol at a concentration of ng/µl. Mobile phase solvents and additives were all LC MS quality and purchased from Sigma Aldrich. Apple extracts were provided by Phytocontrol and extracted according to the EURL- SRM QuPPe methodology. Briefly, apple samples ( g) were prepared by chopping up the sample, freezing, homogenizing with dry ice, adding % formic acid in methanol solution ( ml) and centrifuging ( RPM). Linearity was evaluated by spiking sample extracts at the following levels:.,.,.,.,. and. mg/kg. Deuterated internal standards were used for calibration. All calibration points were analysed in duplicate. Plastic vials were used for analysis to prevent interaction of certain pesticides (e.g. paraquat, diquat and glyphosate) with glass surfaces. SRM transitions and analyte specific MS parameters (Q prebias (V), Q pre-bias (V) and collision energy) were optimised automatically using the SRM optimisation feature available in LabSolutions software. SRM transitions are listed in Table and Table. Preliminary investigations involved the testing of several different analytical columns: SIELC bselisc R ( x.mm, µm); Hypercarb PGC ( x.mm, µm); SeQuant ZiC-HILIC ( x.mm,.µm), SeQuant ZIC-cHILIC ( x.mm,.µm), Scherzo SM-C8 ( x, µm), Scherzo SW-C8 ( x, µm), Fortis Phenyl ( x.mm, µm), Luna Phenyl- Hexyl ( x.mm, µm), and Restek IBD ( x.mm, µm). These columns were tested with several different mobile phase additives including acetic acid, formic acid, ammonium formate, ammonium acetate and ammonium hydroxide (depending on appropriate conditions for each column and the progression of results). Reversed phase, HILIC, and mixed mode chromatography were tested depending on the column suitability for each mode. The final LCMS/MS method conditions are listed in Table. Liquid chromatography UHPLC Analytical column Mobile phase Gradient Column temp. Injection volume Flow rate Mass spectrometry LC/MS/MS Ionisation mode Polarity switching time Pause time Dwell times Interface temperature Heating block Desolvation line Gas Table. LC/MS/MS parameters for Method and Method Method exera UHPLC system ZIC-HILIC ( x.mm,.µm) A = Water mm ammonium formate and.% formic acid B = Acetonitrile Time (mins) %B Time (mins) %B 97.8 68 9 7. 68 97 8 6 Stop o C o C 6µL (µl acetonitrile co-injected) µl.ml/min LCMS-8 Heated electrospray ms ms -ms o C C o C Method exera UHPLC system A = Water % acetic acid B = Methanol % acetic acid. Stop.mL/min Heating gas L/min; drying gas L/min; ebulising gas L/min Hypercarb PGC (mm x.mm, µm)
C8 Compound Ret. time (min) Table. Method MS acquisition parameters, retention time and internal standard Polarity SRM transitions Q (V) CE Q (V) ISTD MS Res. MS Res. Amitrole. Positive 8 > - - - Paraquat d8 Unit Unit 8 > 7 - - - Unit Unit 8 > 8 - - - Unit Unit Chlormequat. Positive > 8-8 -7 - Chlormequat d Unit Unit > 9-8 - - Unit Unit > 6-8 - - Unit Unit Daminozide. Positive 6 > -6 - - Chlormequat d Unit Unit 6 > -6 - -6 Unit Unit 6 > -6 - -6 Unit Unit Diquat. Positive 8 > 7 - - -7 Paraquat d8 Unit Unit 8 > 78 - -9 - Unit Unit 8 > - - - Unit Unit Kasugamycine 7.8 Positive 8 > -8 - -8 Chlormequat d Unit Unit 8 > -8 - - Unit Unit Mepiquat. Positive > 98 - -9 - Mepiquat d Unit Unit > 8 - -6 - Unit Unit > - - - Unit Unit Paraquat 9. Positive 86 > 7 - - - Paraquat d8 Unit Unit 86 > 77 - - -7 Unit Unit 86 > 69 - - -9 Unit Unit Trimesium. Positive 77 > 6 - - - Paraquat d8 Unit Unit 77 > 7 - -7-7 Unit Unit 77 > - - -6 Unit Unit Chlormequat d. Positive 6 > 8 - -9 - Unit Unit Mepiquat d. Positive 7 > - -9-8 Unit Unit Paraquat d8 9. Positive 9 > 78 - - - Unit Unit Compound Table. Method MS acquisition parameters, retention time and internal standard Ret. time (min) Polarity SRM transitions Q (V) CE Q (V) ISTD MS Res. MS Res. Glyphosate.7 Positive 7 > 88-7 -9-8 Glyphosate C Unit Unit 7 > -7-6 -7 Unit Unit 7 > 6-7 -6 - Unit Unit Gluphosinate.9 Positive 8 > 6 - - -6 Maleic hydrazide d Unit Unit 8 > 6 - - - Unit Unit 8 > 9 - -9 - Unit Unit ETU. Positive > -9-8 - ETU d Unit Unit > 6-9 -8 - Unit Unit > 86-9 - -8 Unit Unit Fosethyl 9.9 egative 9 > 8 9 Fosethyl d Unit Unit 9 > 6 Unit Unit 9 > 79 8 Unit Unit Maleic hydrazide.7 Positive > - -7-6 Maleic hydrazide d Unit Unit > 67 - -9-7 Unit Unit > 8 - -7-7 Unit Unit icotine. Positive 6 > -6 - - icotine d Unit Unit 6 > 7-6 - - Unit Unit 6 > -6-7 - Unit Unit Perchlorate. egative 99 > 8 6 Perchlorate 8 Unit Unit 99 > 67 7 Unit Unit > 8 6 Unit Unit PTU. Positive 7 > 8 - -6-9 ETU d Unit Unit 7 > 6 - -9 - Unit Unit 7 > 7 - - -6 Unit Unit ETU d. Positive 7 > 8-8 -9-6 Unit Unit Fosethyl d 9.6 egative > 8 Unit Unit Maleic hydrazide d.6 Positive > - - -7 Unit Unit Glyphosate C.6 Positive 7 > 9 - -8-9 Unit Unit icotine d.7 Positive 66 > - - - Unit Unit Perchlorate 8. egative 7 > 89 7 Unit Unit
(x,,) C8 Results and Discussion Following evaluation of several different analytical columns, mobile phases and mass spectrometer settings, two methods were developed for a range of highly polar pesticides that typically require single residue methods to analyse. A ZIC-HILIC column, a zwitterionic stationary phase covalently attached to porous silica, was used in method to analyse the following; amitrole, chlormequat, daminozide, diquat, kasugamycine, mepiquat, paraquat and trimesium. While a Hypercarb PGC (porous graphitic carbon), which behaves as a strongly retentive alkyl-bonded silica gel, was used in method to analyse the following; glufosinate, glyphosate, ethephon, fosethyl aluminium, maleic hydrazide, perchlorate, ETU, PTU, and nicotine. Three MRM transitions were acquired for each analyte, with exception of two transitions for kasugamycine. Linearity was evaluated for all compounds in the range. mg/kg. mg/kg ( ppb) in apple matrix. The concentration of each calibration level is listed in the experimental section. All seven target compounds achieved excellent correlation coefficients greater than R >.997, using internal standards for quantitation, linear fit and /C weighting. Calibration curves for several compounds are displayed in Figure (using LC method ) and Figure (using LC method ). The linearity results for all target compounds is listed in Table..7 LC Method Chlormequat Paraquat. Diquat Mepiquat.. Amitrole Trimesium.7 Kasugamycine......... 6. 7. 8. 9. min Figure. Target analytes at.mg/kg in apple matrix using a ZIC-HILIC based separation (LC Method ) 6 Mepiquat y =.7x +.66 R² =.9999 Fit; linear, weighting /C, zero not forced 9 8 7 Diquat y =.79x +.899 R² =.9986 Fit; linear, weighting /C, zero not forced 6 Trimesium y =.7x -.978 R² =.998 Fit; linear, weighting /C, zero not forced Paraquat y =.69x -.6 R² =.9996 Fit; linear, weighting /C, zero not forced Figure. Calibration curves for paraquat, mepiquat, trimesium and diquat using a ZIC-HILIC based separation (LC Method )
(x,) C8 Figure displays a chromatogram of each compound at. mg/kg using a ZIC-HILIC based separation (LC method ) and Figure display a chromatogram using a Hypercarb PGC based separation (LC method ). All target analytes were identified at. mg/kg. This concentration is below the European Union (EU) maximum residue limit (MRL) for all of the target analytes in this study. For example, the EU MRL for the following compounds in the majority of commodities is; glyphosate. mg/kg, glufosinate. mg/kg, chlormequat. mg/kg, paraquat., mepiquat. mg/kg, daminozide. mg/kg and ethephon. mg/kg. Consequently, the sensitivity achieved in these methods is far below what is required and therefore dilution of sample extracts is possible in order to reduce matrix effects.. LC Method Maleic hydrazide PTU Perchlorate ETU Glyphosate.. Glufosinate Fosethyl icotine.... 7.... 7.. min Figure. Target analytes at.mg/kg in apple matrix using a Hypercarb PGC based separation (LC Method ). Glyphosate y =.9x +.68 R² =.998 Fit; linear, weighting /C, zero not forced Glufosinate y =.778x +.77 R² =.999 Fit; linear, weighting /C, zero not forced Maleic hydrazide y =.699x +.98 R² =.998 Fit; linear, weighting /C, zero not forced 6 Fosethyl y =.6968x +.886 R² =.997 Fit; linear, weighting /C, zero not forced Figure. Calibration curves for glyphosate, gluphosinate, maleic hydrazide and fosethyl using Hypercarb PGC based separation (LC Method )
C8 Conclusion Two LC-MS/MS methods were developed for the measurement of a range of highly polar pesticides in their underivitised state using the LCMS-8 triple quadrupole mass spectrometer. The developed multi-residue methods offer significant time savings in comparison to single residue methods typically used for analyse of these analytes. All compounds were quantified in the range.. mg/kg with correlation coefficients greater than.997. The excellent sensitivity achieved, which is most cases is far below the EU MRL, offers the opportunity to dilute sample extracts prior to LC-MS/MS injection in order to reduce matrix effects. References. Reference Laboratory for pesticides requiring Single Residue Methods (EURL-SRM). Quick Method for the Analysis of Residues of numerous Highly Polar Pesticides in Foods of Plant rigin involving Simultaneous Extraction with Methanol and LC- MS/MS Determination (QuPPe-Method).. Version 7. Commission Regulation (EC).. o 96/ of the European Parliament and of the Council, maximum residue levels of pesticides in or on food and feed of plant and animal origin. fficial Journal of the European Union, L 7: -6. http://ec.europa.eu/sanco_pesticides/public/index.cfm?event=h omepage&language=e Table. Target analytes linearity results using LC method and LC method Compound R Fit type Weight Method Diquat.9986 Linear /C Method Chlormequat.9988 Linear /C Method Amitrole.998 Quadratic /C Method Kasugamycine.999 Linear /C Method Daminozide.999 Quadratic /C Method Mepiquat.999 Linear /C Method Paraquat.999 Linear /C Method Trimesium.998 Linear /C Method ETU.9998 Linear /C Method Fosethyl.997 Linear /C Method Gluphosinate.999 Linear /C Method Glyphosate.998 Linear /C Method Maleic hydrazide.998 Linear /C Method icotine.998 Linear /C Method Perchlorate.9998 Linear /C Method PTU.999 Linear /C Method First Edition: July, Shimadzu Corporation www.shimadzu.com/an/ Shimadzu Corporation,