The Analysis of Organophosphate Pesticides by LC/MS Application LC-MS Authors Paul Zavitsanos Agilent Technologies, Inc. 2850 Centerville Road Wilmington, DE 19808-1610 USA Paul Yang MOE Ontario Canada Lorna Grey MOE Ontario Canada Abstract Organophosphate pesticides were readily analyzed using liquid chromatography-mass spectrometry with electrospray ion source. Sensitivity and selectivity were significantly better than using a diode-array UV detector. Overview Liquid chromatography-mass spectrometry (LC-MS) is rapidly becoming a routine technique for efficient trace analysis of polar pesticides in various types of samples. In comparison to existing methodologies, such as gas chromatography-mass spectrometry (GC-MS) and ultraviolet (UV) detection, LC-MS considerably simplifies cleanup procedures, reducing both time of analysis and method development time. 1 LC-MS with an electrospray ion (ESI) source avoids the thermal degradation of labile pesticides encountered with GC and eliminates the need for preliminary derivatization to increase compound volatility. Additionally, LC-MS provides unequivocal identification of each pesticide, even if the pesticide was not completely resolved from neighboring eluants. Traditional UV detection cannot provide the required specificity because many of the pesticides within the same class exhibit similar UV spectra. Sample case A mixture of organophosphate pesticides and an internal standard were analyzed using an Agilent 1100 LC/MS with an ESI source (Table 1). Table 1. Mixture of Organophosphate Pesticides Elution Concentration order Compound µg/ml 1 Mevinphos isomer 1 225 0.2 2 Dimethoate 230 0.5 3 Mevinphos isomer 2 225 0.5 4 Dichlorvos 221 0.5 5 Azinphos methyl 318 0.05 6 Parathion methyl 264 0.2 7 Malathion 331 0.5 8 Diazinon 305 0.2 9 Triphenyl orthophosphate* 327 1.0 10 Parathion ethyl 292 0.1 11 Phorate 261 0.1 12 Reldan 322 0.5 13 Ronnel 321 0.1 14 Terbuphos 289 0.2 15 Dursban 350 0.1 16 Ethion 385 0.2 17 Temephos 467 0.1 * Internal standard
Method summary Column 2.1 mm id 5 cm long, filled with 3.5 µm particles, C18 chemistry 20 mm ammonium acetate vs. acetonitrile mobile phase gradient 5 % to 95 % acetonitrile in 4 minutes Hold 2 minutes Splitless 400 µl/min flow 3 µl injection volume Scan data 120 to 600 SIM data as per Table 1. 95 msec dwell/ion in two groups Results Simultaneous UV (220 nm) and MS detector outputs are compared in Figure 1. The MS plot is a composite of all the individual extracted ion chromatograms. Each was obtained at the value given in Table 1, and are separated and stacked in Figure 2 for easy comparison. 5 0-5 -10-15 -20-25 0 2 4 6 8 10 12 14 Normalized UV Plot min. 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0 2 4 6 8 10 12 14 min. MS selected ion mode (SIM), overlayed and normalized Figure 1. Comparison of UV and MS chromatograms. 2
1 2 3 4 5 6 7 8 12 11 10 9 17 467 16 385 15 350 14 289 13 321 322 261 292 327 305 331 264 348 221 230 225 2 4 6 8 10 Minutes Figure 2. Stacked normalized extracted ion chromatograms for compounds 1 through 17. Figures 3 through 6 show the resulting normalized mass ion spectra for each compound included in Table 1. 3
Mevinphos isomer 1 193.0 226.0 283.0 225.0 Dimethoate 232.0 230.0 Mevinphos isomer 2 192.9 225.0 [M+NH4] + 242.9 242.1 Dichlorvos 224.8 239.9 [M+NH4] + 220.9 222.9 237.9 100 150 200 250 300 Figure 3. Stacked normalized ion mass spectra for compounds 1 through 4. 4
Azinphos methyl Malathion 285.0 332.0 331.0 348.1 Diazinon 306.1 305.1 118.9 133.1 150.0 160.0 235.4 260.9 317.9 291.5 290.4 318.8 340.1 132.0 Parathion methyl 265.1 291.4 Background 263.9 290.1 100 150 200 250 300 Figure 4. Stacked normalized ion mass spectra for compounds 5 through 8. 5
Triphenyl orthophosphate 292.1 328.0 327.0 Parathion ethyl 235.1 261.0 293.0 304.9 Phorate 263.0 Reldan 324.9 325.8 321.9 323.9 100 150 200 250 300 Figure 5. Stacked normalized ion mass spectra for compounds 9 through 12. 6
Ronnel 101.9 253.3 244.8 324.0 322.9 324.9 339.1 320.8 Terbuphos 98.0 186.9 198.9 234.9 291.0 289.0 232.9 100 150 200 250 300 Dursban 351.9 Ethion Temephos 386.9 467.0 [M+NH4] + 485.0 484.0 353.9 350.9 325 350 375 400 425 450 475 Figure 6. Stacked normalized ion mass spectra for compounds 13 through 17. 7
Conclusions www.agilent.com When determining organophosphate pesticides using LC-MS with an ESI source: All the tested organophosphate pesticides ionized well and gave definite ions Sensitivity and selectivity are significantly better than using diode-array UV detector Overall chromatography and analysis is simple and straightforward Positive identification and quantification are performed using integrated software For more information, contact your local Agilent sales representative, or visit www.agilent.com. Reference 1. Elbert Hogendoorn and Peit van Zoonen, Journal of Chromatography A, 892 (2000) 435-453. Agilent shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. Information, descriptions, and specifications in this publication are subject to change without notice. Copyright 2001 Agilent Technologies, Inc. Printed in the USA September 13, 2001 5988-3774EN