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Food Control 43 (2014) 110e114

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Food Control

journal homepage: www.elsevier .com/locate/ foodcont

Short communication

The rapid selecting of precursor ions and product ions of thirty-fourkinds of pesticide for content determination by GCeEI/MS/MS

Yun-Bin Jiang a, Mei Zhong b,c, Yu-Ying Ma a,*

aChengdu University of Traditional Chinese Medicine, Chengdu 611137, Chinab Lanzhou Institute of Chemical Physics, Lanzhou 730000, ChinacUniversity of Chinese Academy of Sciences, Beijing 100049, China

a r t i c l e i n f o

Article history:Received 13 December 2013Received in revised form20 February 2014Accepted 4 March 2014Available online 14 March 2014

Keywords:GCeEI/MS/MSPesticide residuesMRMPrecursor ionsProduct ions

* Corresponding author. Tel.: þ86 13678189939.E-mail addresses: ma-yuying@126.com, cdtcmma@

http://dx.doi.org/10.1016/j.foodcont.2014.03.0040956-7135/� 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

Pesticide residues caused great threat to human body health, and all countries protected the health ofhuman body by specifying its upper limit. However, pesticide residues were generally very low, similar totrace analysis and as low as millionth or less, the content determination of pesticide residues was atroublesome problem. With the application and promotion of tandem mass spectrometry, it was able todo trace analysis. GCeEI/MS/MS was a common method for the determination of pesticide residues. Themultiple reaction monitoring (MRM) mode was the most common quantitative method used in GCeEI/MS/MS. It has the characteristics of high sensitivity, good reproducibility, high accuracy, strong anti-interference and high ion flux. Multiple-twin precursor ions, product ions and collision energy ofthirty-four pesticides were provided for MRM. It could play an important role in developing MRMmethod for the quantifying of 34 kinds of pesticide. Meanwhile, the development of MRMmethod for thequantifying of other compounds could also refer to this paper.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Gas chromatography is a common method, used to detectpesticide residues. According to the existing literature, five kinds ofdetector were commonly used for detection of pesticide residues,electron capture detector (ECD), nitrogen phosphorus detector(NPD), flame photometric detector (FPD), flame ionization detector(FID) and mass spectrometry detector (MSD).

Pesticide residues in Brassica vegetables were analyzed by GCeECD and NPD (qozowicka, Jankowska, & Kaczy�nski, 2012). Pesticideresidues among fruits and vegetables were analyzed by GCeECD(Chen et al., 2011; Crentsil, Archibold, Ellis, Beatrice, & Gladys,2012). Residues of pesticides in fruits were determined by GCeECD, NPD and MSD (Berrada et al., 2010). Organophosphoruspesticide residues in Sicilian and Apulian olive oil were analyzed byGCeFPD (Giacomo, Giuseppa, Loredana, & Marcello, 2005).Organophosphorus and pyrethroid pesticides in water weredetermined by GCeFID (Anselmo & Jailson, 2009). A method usedto determine multiclass pesticide residues was established usingGCeMS/MS and LCeMS/MS in olive and olives. Different collision

163.com (Y.-Y. Ma).

energy and capillary voltage values optimization were conductedby performing multiple injections of each analyte. Optimal transi-tions and MS conditions were used for data acquisition in MS/MS(Anagnostopoulos & Miliadis, 2013). A sensitive and selectivemethod for the determination of selected pesticides in fruit wasestablished using chromatography/mass spectrometry with nega-tive chemical ionization. The optimization of MRM conditions hastwo steps. The first step was acquisition in full scanmode in them/z50e400 range. The ions with a high m/z ratio and a high relativeabundance were selected as the precursor ions. The next step wasthe fragmentation of the selected precursor ion for each pesticideby applying different collision energies (between 5 and 40 eV) andthe subsequent selection of adequate fragment ions (BelmonteValles, Retamal, Mezcua, & Fernández-Alba, 2012).

Different detector for different pesticides had different advan-tages. ECD is the most common detector for organochlorine pesti-cide residues. NPD can only be used to monitor some specificpesticides, which include nitrogen and phosphorus. FPD is mainlyused to monitor pesticides, which contain sulfur and phosphorus.FID can be applied to almost all pesticides. Compared with ECD,NPD, FPD and FID, MSD has its unique advantages, which havehigher sensitivity, better reproducibility, higher accuracy, strongeranti-interference and higher flux. Due to the complexity of chem-ical composition of sample, general detector is difficult to eliminate

Fig. 1. The process of MRM method established by GCeEI/MS/MS.

Y.-B. Jiang et al. / Food Control 43 (2014) 110e114 111

interference and detection sensitivity is limited. In recent years, theapplication of tandemmass spectrometry has greatly improved thedetection sensitivity, and has stronger ability to eliminate inter-ference. The MRM mode is the most common method of quanti-tative analysis in tandem mass spectrometry. Furthermore, mostpresent application of GCeMS/MS ion source is electron impactionization (EI) source, whose mass spectrogram has good repro-ducibility. This paper provided relevant researchers with multiple-twin precursor ions and product ions for MRM. The process of MRMmethod established by GCeEI/MS/MS was shown in Fig. 1.

2. Experimental

2.1. Chemicals and reagents

Thirty-four reference substances (22 organochlorines and 12organophosphoruses) were purchased from Dr. EhrenstorferGmbh (Augsburg, Germany) and AccuStandard, Inc (New Haven,USA). Their detailed informations were shown in Table 1. HPLC-

Table 1The information of reference substance.

CAS no. Compound name Purity (%) or concent(mg/mL in methanol)

62-73-7 Dichlorvos 98.010265-92-6 Methamidophos 99.0%30560-19-1 Acephate 98.0118-74-1 Hexachlorobenzene 100.0%1113-02-6 Omethoate 97.0%333-41-5 Diazinon 100.0%319-84-6 a-BHC 98.0%6923-22-4 Monocrotophos 99.0%82-68-8 Pentachloronitrobenzene 99.0%58-89-9 g-BHC 98.5%319-85-7 b-BHC 97.5%60-51-5 Dimethoate 100.0%76-44-8 Heptachlor 99.5%319-86-8 d-BHC 98.4%298-00-0 Parathion-methyl 98.5%121-75-5 Malathion 99.5%309-00-2 Aldrin 98.5%56-38-2 Parathion 99.0%27304-13-8 Oxy-chordane 100 mg/mL1024-57-3 Heptachlor-endo-epoxide 100.0%28044-83-9 Heptachlor-exo-epoxide 100 mg/mL5103-71-9 Cis-chlordane 100.0%5103-74-2 Trans-chlordane 100.0%959-98-8 a-Endosulfan 96.0%72-55-9 P,P0-DDE 98.5%60-57-1 Dieldrin 98.3%950-37-8 Methidathion 99.0563-12-2 Ethion 96.5%789-02-6 O,P0-DDT 98.5%72-54-8 P,P0-DDD 99.0%72-20-8 Endrin 97.0%33213-65-9 b-Endosulfan 98.0%50-29-3 P,P0-DDT 98.5%1031-07-8 Endosulfan sulfate 100.0%

grade n-hexane was purchased from Sinopharm Chemical Re-agent Co., Ltd (Shanghai, China). High purity helium and nitrogenwere made by high purity helium generator and nitrogen gener-ator respectively.

2.2. The preparation of standard solution

The right amount of 34 kinds of pesticide were separately dis-solved in n-hexane to get about 0.1 mg/mL, regarded as stock so-lutions and stored at 2 �C. Stock solutions of 34 kinds of pesticidewere separately diluted in n-hexane to get about 0.5 mg/mL foranalysis. The diluents were filtered by a 0.22 mmmembrane (nylon-66) before analysis.

2.3. Gas chromatographic and mass spectrometric conditions

This analysis was carried out on Agilent Technologies 7890A GCsystem equipped with split/splitless mode and programmed tem-perature vaporizer inlet, and 7000B GC/MS Triple Quad equippedwith electron impact ionization (EI) (Agilent Crop., MA, USA). Theanalysis process was carried out on column 1 (J&W DB-17 ms30 m � 0.250 mm � 0.25 mm; 40 to 320/340 �C) and column 2(Agilent 1.3 m � 180 mm � 0 mm; 450 �C).

The gas chromatographic conditions were: the carrier gas washelium; the flow rates of carrier gas and backflushing were 1 mL/min and 3 mL/min respectively; the inlet temperature was set at230 �C; the mode of inlet was splitless; the injection volume was1 mL; the temperature programming was presented in Table 2; theauxiliary heaters was set at 280 �C; total time of analysis was16.75 min.

ration Identification of product Manufacturers

12530000 Dr. Ehrenstorfer Gmbh14980000 Dr. Ehrenstorfer Gmbh10010000 Dr. Ehrenstorfer Gmbh18779 Dr. Ehrenstorfer Gmbh15730000 Dr. Ehrenstorfer Gmbh22538 AccuStandard, Inc90218 Dr. Ehrenstorfer Gmbh15300000 Dr. Ehrenstorfer Gmbh16730000 Dr. Ehrenstorfer Gmbh14073000 Dr. Ehrenstorfer Gmbh14072000 Dr. Ehrenstorfer Gmbh021604MS-AC AccuStandard, Inc14090000 Dr. Ehrenstorfer Gmbh50405 Dr. Ehrenstorfer Gmbh15890000 Dr. Ehrenstorfer Gmbh14710000 Dr. Ehrenstorfer Gmbh10090000 Dr. Ehrenstorfer Gmbh15880000 Dr. Ehrenstorfer Gmbh213091057 AccuStandard, Inc071012KC AccuStandard, Inc212111006 AccuStandard, Inc21321 AccuStandard, Inc23066 AccuStandard, Inc13121000 Dr. Ehrenstorfer Gmbh00331 Dr. Ehrenstorfer Gmbh12590000 Dr. Ehrenstorfer Gmbh15020000 Dr. Ehrenstorfer Gmbh71009 Dr. Ehrenstorfer Gmbh80820 Dr. Ehrenstorfer Gmbh80718 Dr. Ehrenstorfer Gmbh13160000 Dr. Ehrenstorfer Gmbh13122000 Dr. Ehrenstorfer Gmbh71011 Dr. Ehrenstorfer Gmbh012511KS AccuStandard, Inc

Table 2The temperature programming.

Rate (�C/min) Value (�C) Hold time (min) Run time (min)

Initial 60 2 2Ramp 1 40 250 0 6.75Ramp 2 10 300 5 16.75

Y.-B. Jiang et al. / Food Control 43 (2014) 110e114112

The mass spectrometric conditions: the electron energy andtemperature of ion source was set at �70 eV and 280 �C respec-tively; the monitoring range of m/z was set according to molecularmass of each compound; the solvent delay was 3.5 min; it was theprecursor ions of each pesticide that was obtained in MS1 Scanmode; precursor ions passed MS1 in MS1 SIM (Selecting IonMonitoring, SIM) mode, then ions of different mass-to-charge ratiowere obtained in the collision cell with different collision energy,and at last the best collision energy and product ions were chosenin product ions mode; the flow rate of quench gas (helium) and

Fig. 3. Optimization of collision energy of 291.1 m/z of g-BHC:

Fig. 2. The EI scan fi

collision gas (nitrogen) were 2.25 mL/min and 1.5 mL/min sepa-rately in collision cell.

3. Results and discussion

3.1. The choice of precursor ions

Ions of each pesticide from ion sources were detected in MS1Scan mode, and ions of high abundance and mass-to-charge ratiowere chosen as the precursor ions. 219.1, 216.9, 183.0 and 181.1m/zwere chosen as the precursor ions of g-BHC (Fig. 2). The selection ofprecursor ions of other pesticides was similar to g-BHC.

3.2. Optimization of collision energy and the choice of product ions

At first, collision energy was set at 10, 20, 30 and 40 V to lookingfor preliminary appropriate collision energy, the collision energywith high abundance of product ions in product ions mode. Further,

A (10 V); B (20 V); C (30 V); D (40 V); E (50 V); F (60 V).

gure of g-BHC.

Table 3The precursor ion, product ion and collision energy of 34 kinds of pesticide.

Compound name Retentiontimes (min)

Molecularion (m/z)

Precursor ion (m/z) Product ion (m/z) Collision energy (V)

Dichlorvos 6.800 221.0 187.1; 187.1; 185.0; 185.0; 144.9; 109.0; 109.0 109.0; 93.0; 109.0; 93.0; 109.0; 79.0; 47.0 15; 10; 15; 10; 10; 5; 10Methamidophos 7.165 141.1 141.0; 141.0; 125.9; 95.0; 95.0 95.0; 80.0; 96.0; 79.0; 64.0 5; 15; 10; 10; 10Acephate 7.939 183.2 142.0; 136.0; 125.0; 125.0 96.0; 94.0; 79.0; 47.0 5; 10; 5; 15Hexachlorobenzene 8.766 284.8 285.8; 283.8; 283.8; 281.8; 281.8; 248.9; 248.9 250.9; 248.8; 213.9; 246.9; 211.9; 214.0; 179.0 15; 15; 30; 15; 30; 15; 30Omethoate 8.807 213.2 155.9; 155.9; 140.9; 126.0; 110.0; 110.0 110.0; 79.0; 111.0; 79.1; 95.0; 79.0 5; 20; 10; 5; 10; 15Diazinon 8.840 304.4 276.0; 276.0; 199.0; 199.0; 179.1; 179.1; 137.1; 137.1 179.1; 137.1; 135.0; 93.0; 164.1; 137.1; 84.0; 54.0 5; 25; 10; 15; 20; 20; 10; 20a-BHC 8.873 290.8 219.0; 219.0; 216.9; 216.9; 182.9; 182.9; 180.9; 180.9 183.0; 147.0; 181.0; 145.0; 147.0; 109.0; 145.0; 109.0 5; 15; 5; 15; 15; 30; 15; 30Monocrotophos 9.016 223.2 192.0; 192.0; 127.0; 127.0; 109.0; 97.0 127.0; 66.0; 109.0; 95.0; 79.0; 82.0 10; 20; 10; 15; 5; 10Pentachloronitrobenzene 9.107 295.4 236.9; 236.9 118.9; 142.9 25; 30g-BHC 9.257 290.8 219.1; 216.9; 183.0; 183.0; 181.1; 181.1 182.8; 181.0; 147.0; 109.0; 145.0; 109.0 5; 5; 15; 30; 15; 30b-BHC 9.369 290.8 218.9; 216.9; 183.0; 183.0; 181.0; 181.0 183.1; 181.1; 147.0; 109.0; 145.0; 109.0 5; 5; 15; 30; 15; 30Dimethoate 9.413 229.3 142.9; 142.9; 124.9; 124.9 111.0; 47.0; 79.0; 47.0 10; 25; 10; 25Heptachlor 9.603 373.3 336.6; 273.7; 273.7; 271.7; 236.9; 236.9 265.7; 238.9; 236.9; 236.9; 142.9; 118.8 15; 15; 15; 15; 25; 25d-BHC 9.749 290.8 219.0; 219.0; 217.0; 217.0; 183.1; 183.1; 181.1; 181.1 183.1; 147.0; 181.1; 145.1; 147.1; 109.0; 145.0; 109.0 5; 20; 5; 20; 15; 30; 15; 30Parathion-methyl 9.895 263.2 262.9; 262.9; 233.0; 125.0; 125.0 109.0; 79.0; 109.0; 79.0; 47.0 10; 30; 10; 5; 10Malathion 9.963 330.4 172.9; 172.9; 157.8; 157.8; 143.0; 143.0; 127.0; 127.0 117.0; 99.0; 125.0; 47.0; 111.0; 47.0; 99.0; 55.0 10; 15; 5; 25; 10; 25; 5; 5Aldrin 9.986 364.9 292.8; 264.9; 264.9; 264.9; 262.9; 262.9; 254.9 185.9; 229.9; 194.9; 192.9; 192.9; 190.9; 220.0 40; 20; 35; 35; 35; 35; 20Parathion 10.122 291.3 291.0; 291.0; 186.0; 186.0; 155.0; 155.0 109.0; 81.0; 169.0; 140.0; 125.0; 97.0 10; 25; 10; 5; 5; 15Oxy-chordane 10.413 423.8 386.7; 236.9; 236.9; 184.9; 184.9; 114.9; 114.9 262.7; 142.9; 119.0; 121.0; 85.0; 87.0; 51.1 15; 25; 25; 15; 30; 15; 25Heptachlor-endo-epoxide 10.596 389.3 354.8; 354.8; 352.9; 352.9; 263.0; 263.0; 236.9; 236.9 318.8; 264.9; 316.9; 262.9; 193.1; 191.1; 143.0; 119.0 5; 15; 5; 15; 35; 35; 25; 25Heptachlor-exo-epoxide 10.727 389.3 352.7; 352.7; 252.9; 252.9; 216.9; 216.9; 182.9; 182.9 288.7; 252.7; 217.9; 183.0: 181.9; 147.0; 154.9; 118.9 10; 20; 20; 35; 20; 35; 15; 25Cis-chlordane 10.820 409.8 375.0; 375.0; 372.8; 372.8; 271.9; 236.9; 236.9 300.9; 266.0; 300.8; 265.8; 236.9; 142.9; 118.9 10; 20; 10; 20; 15; 30; 30Trans-chlordane 10.975 409.8 374.9; 372.8; 372.8; 271.6; 236.9; 236.9 265.9; 300.7; 265.8; 236.8; 143.0; 119.0 15; 10; 15; 15; 25; 25a-Endosulfan 11.107 406.9 276.7; 262.8; 236.9; 236.9; 194.9; 194.9; 194.9 241.9; 192.9; 143.0; 119.0; 160.0; 159.0; 125.0 15; 30; 25; 30; 5; 5; 20P,P0 -DDE 11.167 318.0 317.8; 317.8; 315.8; 246.1; 176.0 248.0; 246.0; 246.0; 176.2; 150.1 15; 15; 15; 30; 25Dieldrin 11.492 380.9 345.0; 277.0; 262.9; 262.9; 237.0; 237.0 262.7; 241.0; 193.0; 191.0; 142.9; 118.9 5; 5; 35; 35; 25; 25Methidathion 11.492 302.3 145.0; 145.0; 124.9; 124.9; 93.0; 85.0 85.0; 58.0; 19.0; 47.0; 63.0; 58.0 5; 15; 5; 15; 5; 5Ethion 11.850 384.5 231.0; 231.0; 152.9; 124.9; 120.9 175.0; 129.0; 96.9; 97.0; 65.0 10; 20; 10; 10; 10O,P0-DDT 11.964 354.5 237.0; 237.0; 235.0; 235.0; 199.0; 165.0; 165.0 199.1; 165.2; 199.1; 165.2; 163.1; 139.1; 115.1 15; 20; 15; 20; 35; 30; 35P,P0-DDD 11.964 320.0 236.9; 234.9; 234.9; 199.0; 199.0; 165.1; 165.1 165.2; 199.1; 165.1; 164.1; 163.1; 139.1; 115.1 20; 15; 20; 20; 30; 35; 35Endrin 12.016 380.9 344.7; 316.7; 316.7; 262.8; 262.8; 244.8; 244.8 280.8; 280.8; 100.8; 227.9; 193.0; 210.0; 173.0 5; 5; 10; 20; 35; 10; 30b-Endosulfan 12.335 406.9 276.7; 236.8; 206.9; 194.9; 194.9 240.9; 118.8; 172.0; 158.9; 124.9 5; 30; 15; 10; 25P,P0-DDT 12.424 354.5 237.0; 235.0; 235.0; 212.0; 165.0 165.2; 199.2; 165.2; 176.1; 115.1 20; 15; 20; 30; 30Endosulfan sulfate 13.034 422.9 386.6; 386.6; 273.8; 273.8; 271.9; 271.9; 229.0 288.9; 252.9; 238.9; 236.9; 237.0; 235.0; 194.0 5; 10; 15; 15; 15; 15; 25

The precursor ion, product ion and collision energy were listed in separate columns according to the corresponding order.

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Y.-B. Jiang et al. / Food Control 43 (2014) 110e114114

more appropriate collision energy was found by reducing thechange of collision energy on the preliminary appropriate collisionenergy.182.8m/z and 5 Vwere separately chosen as the product ionand collision energy of 291.1m/z of g-BHC by changing the collisionenergy (Fig. 3). The selection of product ions and collision energy ofother pesticides was similar to g-BHC.

3.3. The precursor ions, product ions and collision energy of 34kinds of pesticide

The precursor ions, product ions and collision energy of 34 kindsof pesticide were chosen by “Sections 3.1 and 3.2”. These resultswere shown in Table 3.

3.4. How to select appropriate precursor ions and product ions inMRM mode

According toTable 3, each pesticide hadmultiple-twin precursorions andproduct ions forMRM.Different precursor ions andproductions were suitable for different sample. However, how to select thebest appropriate precursor ions and product ions to monitor? Dif-ferences in abundance of standard substance A and standard sub-stance B (A and Bwere same standard substance, Awas dissolved inn-hexane, B was dissolved in blank substrate) was the criterion forchoosing of precursor ions and product ions. The smaller the dif-ference was, the smaller the interference of the substrate was.

3.5. The selecting of quantification transition and confirmationtransition

A transition was composed of a precursor ion and a product ion.Generally, two transitions were a must to complete contentdetermination. One was used for the confirmation and the otherone was used for the quantification. The transition of high responsewas used as the quantification of compound and another was usedas the confirmation of the compound, but this was not absolute. Ifthe peak shape and resolution of the transition of high responsewas not good, the transition of low response can be used as thequantification of compound.

3.6. How does backflushing improve analysis?

Backflushing had two roles in gas chromatography. Onewas thatbackflushing can unload heavier component, the other one wasprolong the service life of chromatographic column. Moreover, theunloading of heavier component can shorten the analysis time.

3.7. The importance of chromatographic column aging

The purposes of aging were that the residual solvents in columnor volatile substances were removed and stationary liquid can bemore evenly assigned on the carrier, etc. Aging can reduce

background noise due to loss of column and improve the accuracyof quantification. Generally, aging had a few principles and theywere as follows:

1) Generally, the highest temperature of aging should be lowerthan the chromatographic column top temperature around10 �C and multistage programmed temperature was used foraging.

2) According to the percentage of stationary liquid to set upreasonable aging temperature, the lower content of stationaryliquid was, the lower aging temperature was.

3) Aging timewas related to the sensitivity and type of the detectorand the higher the sensitivity was, the longer the aging timewas.

4) Aging time also depended on the characteristics of stationaryliquid. Generally, the aging time of chromatographically purestationary liquid was less than commercial pure stationaryliquid

5) The larger the polarity of sample was, the longer the aging timewas relatively.

4. Conclusions

The multiple-twin precursor ions and product ions of 34 pesti-cides were provides. According to different samples, appropriateprecursor ions and product ions could be quickly chosen for contentdetermination in MRM mode. The method, optimization of pre-cursor ions, product ions and collision energy, provided clear andconcise thinking for researchers to develop precursor ions andproduct ions of other compounds for MRM.

References

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Anselmo, S. P., & Jailson, B. A. (2009). Development, validation and application of aSDME/GCeFID methodology for the multiresidue determination of organo-phosphate and pyrethroid pesticides in water. Talanta, 79, 1354e1359.

Belmonte Valles, N., Retamal, M., Mezcua, M., & Fernández-Alba, A. R. (2012).A sensitive and selective method for the determination of selected pesticides infruit by gas chromatography/mass spectrometry with negative chemical ioni-zation. Journal of Chromatography a, 1264, 110e116.

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qozowicka, B., Jankowska, M., & Kaczy�nski, P. (2012). Pesticide residues in Brassicavegetables and exposure assessment of consumers. Food Control, 25, 561e575.