Pesticides and Their Degradation Products Including Metabolites: Chromatography-Mass Spectrometry Methods

Renata Raina-Fulton; Nicole Dunn; Zhen Xie

doi:10.5772/68074

Abstract

This chapter reviews the selection of chromatography-mass spectrometry methods for the analysis of organophosphorus pesticides, pyrethroid insecticides, carbamates, and phenylureas. Options with different GC-MS, GC-MS/MS, and LC-MS/MS methods will be discussed for inclusion of the targeted pesticides. In addition, methods for the analysis of metabolites of these chemical classes of pesticides are investigated, including the feasibility of simultaneous analysis with parent pesticides. In some cases, a targeted approach is required for the analyses of metabolites. These methods apply to a wide variety of sample matrices including environmental (air, water, and soil), food (fruits, vegetation, or food products), and biological samples (urine and blood). The focus of the chapter is on MS detection approaches with consideration of the chromatographic separation conditions as required. A short discussion of multiresidue analysis methods and/or where feasible, other chemical classes or selected pesticides from these chemical classes can be analyzed in existing methods is included.

Keywords

gas chromatography-mass spectrometry (GC-MS)
gas chromatography-tandem mass spectrometry (GC-MS/MS)
liquid chromatography-tandem mass spectrometry (LC-MS/MS)
carbamates
organophosphorus pesticides (OPs)
phenylureas
pyrethroids
metabolites
degradation products

Author Information

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Renata Raina-Fulton*
- Department of Chemistry & Biochemistry, Trace Analysis Facility, The University of Regina, Regina, SK, Canada
Nicole Dunn
- Department of Chemistry & Biochemistry, Trace Analysis Facility, The University of Regina, Regina, SK, Canada
Zhen Xie
- Department of Chemistry & Biochemistry, Trace Analysis Facility, The University of Regina, Regina, SK, Canada

*Address all correspondence to: renata.raina@uregina.ca

1. Introduction

Organophosphorus pesticides, pyrethroids, carbamates, and phenylureas remain important chemical classes of pesticides that require chemical analysis by gas chromatography-mass spectrometry (GC-MS), gas chromatography-tandem mass spectrometry (GC-MS/MS), or liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. The most diverse range of chromatography-mass spectrometry methods is available for these chemical classes of pesticides with method selection often based upon sensitivity and selectivity needs (see Figure 1). The chapter will discuss selection of methods for chemical analysis for each of these chemical classes of pesticides along with the feasibility of separate or simultaneous analysis of metabolites and degradation products of these parent pesticides. The focus of this chapter is on the chromatography-mass spectrometry aspects of the methods. Extraction and clean-up or pre-concentration procedures for the target analytes from sample matrices will also influence the magnitude of matrix enhancement or suppression in the MS detection and column choice (or separation conditions used) to minimize the influence of matrix peaks. Further discussion on sample preparation procedures has been recently reviewed [1, 2].

Figure 1.
Options for the chromatography-mass spectrometric analysis of major chemical classes of pesticides and their metabolites or degradation products.

2. Organophosphorus pesticides and their degradation products or metabolites

Organophosphorus pesticides (OPs) include both organophosphates ((RO)₃PO) and organothio phosphates ((R₁O)₃PS, R(R₁O)₂PS, RS(R₁O)₂PS with OR₁ typically methoxy or ethoxy group) as shown in Figure 1. Common organophosphates analyzed include bromofenvinphos, chlorfenvinphos, dichlorvos, mevinphos, and tetrachlorvinphos [3–6]. The majority of OPs analyzed (see Table 1) are organothiophosphates including aliphatic organothiophosphates (chlormephos, demephion-O and S, disulfoton, ethion, ethoprofos, malathion, phorate, and sulfotep) [3–10], aliphatic amide organothiophosphates (dimethoate, o-methoate) [4, 6, 9, 10], heterocyclic organothiophosphates (coumaphos, azinphos-methyl, azinphos-ethyl, phosmet, pyrazophos, chlorpyrifos-methyl, chlorpyrifos-ethyl, diazinon, pirimiphos) [3–10], phenyl organothiophosphates (bromophos-methyl, bromophos-ethyl, carbophenothion, dichlofenthion, fenchlorphos, fenitrothion, fenthion, parathion-methyl, parathion-ethyl, prothiofos, sulprofos) [3, 5–9] and phosphonothioates (fonofos, trichloronat, cyanofenphos, leptophos, fenamiphos, and acephate) [3, 4, 6, 7].

OP	SIM m/z (quantitative, confirmation)	Ref.	SRM m/z (quantitative, confirmation)	Ref.
Acephate	136	[10]	136→42, 136→94	[3]
Aspon	211, 253	[1]	378→210, 378→115	[7]
Azinphos-methyl			160→105, 160→132	[3]
Azinphos-methyl			132→104	[6]
Azinphos-ethyl			160→105, 160→132	[3]
Azinphos-ethyl			132→04	[6]
Bromfenvinphos-methyl			295→295	[5]
Bromfenvinphos-ethyl			267→159	[5]
Bromophos-ethyl			359→303, 359→331	[3, 6]
Bromophos-ethyl			359→303	[5]
Bromophos-methyl			331→286, 331→316	[3, 6]
Bromophos-methyl			331→331	[5]
Carbofenothion	157, 342	[1]	342→157, 342→143	[7]
Chlormefos			234→121, 234→154	[3]
			243→121	[5]
			235→171, 235→199	[6]
Chlorphenvinphos			267→159, 323→267	[3]
			323→267	[5]
			267→159	[6]
Chlorpyrifos-methyl	286, 125	[1]	321→268, 321→208	[7]
	286	[10]	286→136, 286→241	[3]
	286, 288, 125	[17]	286→93	[5]
			286→208, 286→286	[6]
Chlorpyrifos-ethyl	97, 197	[1]	349→208, 349→40	[7]
	199	[10]	314→258, 314→286	[3, 6]
	97, 197	[11]	314→258	[5]
Coumaphos	362	[10]
Cyanofenphos			185→157, 157→110	[3]
Cyanofenphos			157→139, 157→110	[6]
Demeton-o	88, 60	[11]
Diazinon	137, 179	[1]	304→179, 304→137	[7]
	304	[10]	304→137, 304→179	[3]
	137, 304	[11]	304→179	[5, 6]
	287, 302, 288	[17]
Diazinon-d₁₀	314	[1]	314→185	[7]
Dichlofenthion	223, 97	[1]	314→223, 319→81	[7]
			279→222, 279→251	[3]
			279→223	[5]
			279→223, 279→251	[6]
Dichlorvos	185	[10]	185→93	[5]
Dichlorvos	185	[10]	221→141, 221→145	[6]
Dimethoate	125	[10]	230→199	[6]
	87, 125	[11]
	87, 93, 125	[17]
Disulfoton	88, 60	[11]	274→88	[5]
Dyfonate	109, 137	[1]	246→137, 246→109	[7]
Ethion	231, 97	[1]	384→231, 384→203	[7]
Ethion	231, 384	[11]	231→175, 231→203	[3]
Ethoprophos			158→97, 158→114	[3]
			158→97	[5]
			243→131, 243→173	[6]
Fenamiphos			303→154, 303→180	[3]
Fenchlorphos	125, 287	[1]	320→285, 320→204	[7]
Fenchlorphos	125, 287	[1]	285→270	[5]
Fenitrothion	277, 125	[1]	277→260, 277→109	[7]
	109, 125	[11]	260→109, 260→125	[3]
			277→260	[5]
			260→125	[6]
Fenthion	278, 125	[11]	278→125, 278→245	[3]
			278→109	[5]
			278→135	[6]
Fonophos			246→109, 246→137	[3]
Fonophos			246→137, 246→109	[6]
Leptophos	171, 377	[1]
Malathion	173, 125	[1]	173→ 99	[5]
	173, 125, 93	[17]	173→127	[6]
	93, 125	[11]
o-methoate	156	[10]
Mevinphos	192	[10]	192→127, 192→164	[3]
			192→127	[5]
			193→127	[3]
Parathion ethyl	97, 291	[1]	291→109, 291→137	[12]
	291, 109	[11]	291→91, 291→109	[8]
			291→109	[3]
			291→263, 291→143	[18]
Parathion methyl	109, 125	[11]	263→79, 263→109	[8]
			263→109	[3]
			263→136, 263→246	[18]
Phorate	121, 75	[1]	260→75, 263→231	[12]
Phorate	121, 75	[1]	231→129	[3]
Phosmet	160	[10]	160→77	[3]
Pirimiphos-ethyl			333→163, 333→168	[3]
			316→166	[5]
			318→182, 318→166, 318→246	[6]
Pirimiphos-methyl			290→125, 290→151	[3]
			290→125	[5]
			290→151	[6]
Prothiofos			309→221, 309→239	[3]
			162→63	[5]
			309→239, 309→281	[6]
Pyrazophos			265→138, 265→210	[3]
			221→93	[5]
			265→210	[6]
Quinalphos			298→156, 298→190	[3]
			146→91	[5]
			146→118	[11]
Sulfoprofos	140, 322	[1]	322→156, 322→97	[7]
Sulfoprofos	140, 322	[1]	322→156, 322→139	[3]
Sulfotep	322, 202	[1]	322→202, 322→146	[7]
	322, 97	[11]	322→146, 322→266	[3]
			322→146	[5]
Tetrachlorvinphos			329→109	[3, 5]
Tetrachlorvinphos			331→109	[6]
Tokuthion	113, 267	[1]	344→328, 344→73	[7]
Tolclophos methyl			265→220, 265→250	[3]
			265→250	[5]
			265→220, 265→215	[6]
Tributylphosphorotrithioite	169, 57	[1]	314→115, 314→113	[7]
Trichloronate	109, 297	[1]

Table 1.

Selected ion monitoring (SIM) or selected reaction monitoring (SRM) transitions for organophosphorus pesticides (OPs) by GC-EI-MS or GC-EI-MS/MS methods.

OPs are both GC-MS and LC-MS/MS amenable and the choice often depends upon instrument availability, what other pesticide chemical classes are analyzed for and whether there is a need to also analyze degradation products or metabolites of OPs [9, 12, 13]. In general, a greater diversity of OPs has been analyzed simultaneously by GC-MS or GC-MS/MS methods as compared to LC-MS/MS. For analysis of OPs by GC-MS methods, electron impact ionization (EI) remains the most widely used due to its ease of operation and ability to provide spectral library matches (see Table 1) [3–10]. Other pesticide classes that are most frequently analyzed with OPs by GC-MS include OCs, pyrethroids, and a few selected azole fungicides, strobilurin fungicides and carbamates [3, 5, 7, 9, 14].

Selection ion monitoring (SIM) with EI does not always meet sensitivity or selectivity needs or provide information on the molecular weight for some OPs due to the high amount of fragmentation in the EI source. OPs are prone to fragmentation in the EI source such that the molecular ion is often too low in abundance to monitor such that fragment ions are used for quantitation and confirmation analysis [3–7, 9, 10]. Positive or negative chemical ionization may be selected to obtain molecular weight confirmation, however, even with negative chemical ionization (NCI) significant amount of fragmentation of OPs may occur in the ion source although typically few fragment ions are observed in NCI as compared to EI [7, 10]. Electron capture in NCI can occur by dissociate electron capture and the structure of the OP may lead to more stable negatively charged fragment ions than the molecular ion. PCI is generally not selected for quantitative analysis as it does not provide significant improvements in selectivity over EI, while NCI is used for OPs, organochlorines (OCs), and pyrethroids when additional sensitivity or selectivity is required [7, 10]. OPs, organochlorines, and pyrethroids that contain halogen atoms or nitro groups often have lower detection limits with NCI than EI. For example, diazinon and malathion (see structures in Figure 2) have better sensitivity with GC-EI-MS than GC-NCI-MS, while chlorpyrifos-ethyl (chlorinated) and parathion-ethyl (contains a nitro group) have good sensitivity with GC-NCI-MS [7]. The ³⁷Cl or ⁸¹Br isotopes of the molecular ion or fragment ions can be used for confirmation analysis with GC-EI-MS such as for chlorpyrifos methyl (m/z = 288); however, as there is a high degree of fragmentation of OPs with EI, generally more than two fragment ions of higher abundance than the isotope ions can be selected for quantitation and confirmation [3, 5–7, 9, 10].

Figure 2.
Structures of common organophosphorus pesticides (OPs) from different subclasses. OP subclasses include organophosphates (tetrachlorvinphos), aliphatic organothiophosphates (malathion, phorate), heterocyclic organothiophosphates (chlorpyrifos ethyl and diazinon), phenyl organothiophosphates (bromophos), and phosphonothioates (leptophos).

Most halogenated OPs observed better sensitivity with GC-NCI-MS than GC-EI-MS or GC-EI-MS/MS [7]. To provide additional selectivity, GC-EI-MS/MS has been used; however, when the molecular ion is selected as the precursor ion for collision-induced dissociation (CID), the sensitivity is lower than when NCI in SIM mode is used [7]. If the OR₁ group is an ethoxy group, CID of the molecular ion may lead to loss of ethene (C₂H₄) from the ethoxy group and if the OP is halogenated, the loss of halogen radical (e.g., Cl radical) is also frequently observed [6]. For example, the SRM 349→286 of chlorpyrifos corresponds to CID of the molecular ion (M^+•) to form fragment ion F⁺ (Cl₂NC₄HOPS(OC₂H₅)(OH)⁺) as a result of loss of C₂H₂ from an ethoxy group and Cl radical from the aromatic R group. Phorate observes loss of ethyl from the aliphatic R group (SRM: 260→231) to form (⁺SCH₂SPS(OC₂H₅)₂) [5, 7]. As phorate has an aliphatic R group, fragmentation within the R group can result in a stable fragment ion CH₃CH₂SCH₂⁺ at m/z = 75 (SRM: 260→75). The fragment ion at m/z = 231 can undergo further fragmentation through loss of two molecules of ethene from the two ethoxy groups and neutral loss of SCH₂ to form SPS(OH)₂⁺ corresponding to ion at m/z=129 (SRM: 231→129 observed). For (RO)PS(OR₁)₂ where OR₁ is methoxy, CID of the molecular ion will either form [PS(OR₁)₂]⁺ with loss of OR radical or a thiono-thiolo rearrangement may occur such that [PO(OR₁)₂]⁺ is formed with loss of SR radical as observed for fenthion 278→125 and 278→109, respectively [3, 5]. Thiono-thiolo rearrangements have been proposed for fragmentation of diazinon in LC-MS/MS [15].

To improve the sensitivity of GC-EI-MS/MS, the precursor ion can be selected as an abundant fragment ion rather than the molecular ion (see Table 1). For bromophos-methyl (monoisotopic mass 364) and bromophos-ethyl (monoisotopic mass 392), the fragment ions at m/z = 331 and m/z = 359, respectively are selected for precursor ions (SRM 331→286 and 359→303, respectively; see Table 1) and correspond to the either the ³⁷Cl or ⁸¹Br isotope of [M-Cl]⁺[3, 6]. The R groups of OPs vary substantially and can play a significant role in the fragmentation pathway that dominates. For some OPs, the most abundant fragment ion available for CID is R+. For example, azinphos-methyl and azinphos-ethyl fragmentation at S-R bond of RS(OR₁)₂PS to produce R⁺ and ion at m/z = 160 is the dominant fragment ion formed by loss of the S(OR₁)₂PS radical in the EI ion source. Both azinphos-ethyl and azinphos-methyl monitor the SRM transitions at m/z of 160→105, and 160→132 for quantitation and confirmation analysis [3, 6]. The m/z = 160 fragment ion undergoes collision-induced dissociation through loss of N₃CH or C₂H₂ to give fragment ions at 105 and 132, respectively.

Metabolite or degradation product analysis has become of increasing importance for biological monitoring studies (urine or blood) and environmental studies (atmosphere or surface water) [8, 14, 16–21]. Organophosphorus pesticides can be grouped into organophosphates and organothiophosphates with different R-group substituents. Alkylphosphates (dimethylphosphate and diethylphosphate) and alkylthiophosphates (dimethylthiophosphate, dimethylethylthiophosphate, dimethyldithiophosphate, and dimethyldithiophosphates) are formed from metabolism of OPs. They can be analyzed by GC-MS methods following a derivatization step with N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) to form tert-butyldimethylsilyl derivatives (GC-EI-MS); 2,3,4,5,6-pentafluorobenzylbromide (PFBBr) to form pentafluorobenzylbromide derivatives (GC-NCI-MS); and 1-chloro-3-iodropane (CIP) to form chloropropyl ethers (GC-PCI-MS) (see Table 2) [3, 14, 16, 17]. There has been a gradual shift from use of MTBSTFA derivatives that are analyzed by GC-EI-MS to PFBBr-derivatives that can be analyzed by negative chemical ionization for added sensitivity and selectivity, and CIP derivatives that are analyzed with positive chemical ionization.

OP degradation product, derivatization agent	Parent	SIM m/z (quantitative, confirmation) EI	Ref	SRM m/z (quantitative, confirmation)	Ref
Diazinon oxon (oxadiazinon)	diazinon			175→112, 258→112	[7]
Dibutylphosphate, PFBBr (IS)	OP	335, 279	[12, 13, 20]	209→79^NCI	[14]
2,4-Dichlorophenol, MTBSTFA	dichlofenthion	219, 221	[8]
2,5-Dichlorophenol, MTBSTFA	p-dichlorobenzene	221, 219	[8]
Diethyldithiophosphate, PFBBr	OP	366, 185	[18]	185→111, 185→157^NCI	[14]
Diethyldithiophosphate, CIP	OP	366, 185, 157	[12, 13, 20]	263→153, 265→153^PCI	[16, 17]
Diethylphosphate, MTBSTFA	OP	211, 155	[8]	153→79, 153→125	[14]
Diethylphosphate, PFBBr	OP	258, 334	[18]	231→127, 233→127^PCI	[16, 17]
Diethylphosphate, CIP	OP	334, 278, 258	[12, 13, 20]
Diethylthiophosphate, MTBSTFA	OP	227, 199	[8]	169→95, 169→141^NCI	[14]
Diethylthiophosphate, PFBBr	OP	350, 274	[18]	247→191, 249→191^PCI	[16, 17]
Diethylthiophosphate, CIP	OP	350, 274, 169	[12, 13, 20]
Diisopropylphosphate (IS), MTBSTFA	OP	155, 239	[8]
Dimethyldithiophosphate, PFBBr	OP	338, 157	[12, 13, 20]	157→112, 157→142^NCI	[14]
Dimethyldithiophophate, CIP	OP			235→125, 235→125^PCI	[16, 17]
Dimethylphosphate, MTBSTFA	OP	183, 153	[18]	125→63, 125→79^NCI	[14]
Dimethylphosphate, PFBBr	OP	306, 110	[18]	203→127, 205→127^PCI	[16, 17]
Dimethylphosphate, CIP	OP	306, 307, 194	[12, 13, 20]
Dimethylthiophosphate, MTBSTFA	OP	199, 169	[8]	141→126, 141→96^NCI	[14]
Dimethylthiophosphate, PFBBr	OP	322, 211, 110	[12, 13, 20]	219→143, 221→143^PCI	[16, 17]
Dimethylthiophosphate, CIP	OP
Fenamiphos sulfone	fenamiphos			292→213, 320→292	[3]
Fenamiphos sulfoxide	fenamiphos			304→122, 304→196	[3]
2-Isopropyl-6-methyl-4-pyrimidinol, MTBSTFA	diazinon	209, 210	[19]
3-Methyl-4-(methylthio)phenol, MTBSTFA	fenthion	268, 196	[14]
6-Methyl-2-(1-methylethyl)4(1H)-pyrimidinone	diazinon	137, 152, 124	[19]
3-Methyl-4-nitrophenol, MTBSTFA	fenitrothion	267, 210	[8]	152→122, 152→107^NCI	[14]
3-Methyl-4-nitrophenol, PFBBr	fenitrothion
3,5,6-Trichloro-2-pyridinol, MTBSTFA	chlorpyrifos	254, 258	[8]	196→35, 198→35^NCI	[14]
3,5,6-Trichloro-2-pyridinol, PFBBr	chlorpyrifos	256, 254, 258	[21]
Paraoxon methyl	parathion methyl			230→106, 230→136	[3]
Phosmet oxon	phosmet			160→77, 160→133	[3]

Table 2.

Selected ion monitoring (SIM) or selected reaction monitoring (SRM) transitions for organophosphorus pesticides (OPs) degradation products including metabolites by GC/MS or GC/MS/MS methods.

Electron ionization unless noted.

MTBSTFA, N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide forms tert-butyldimethylsilyl derivatives; PFBBr, 2,3,4,5,6-pentafluorobenzylbromide forms pentafluorobenzylbromide derivatives; CIP, 1-chloro-3-iodropane forms chloropropyl ethers; NCI, negative chemical ionization; PCI, positive chemical ionization.

The analysis of OPs by LC-ESI⁺-MS/MS has grown [11, 22–39]. OPs that are amenable to electrospray ionization often have lower detection limits than with GC-MS methods particularly for those OPs most widely studied, including azinphos-methyl, chlorpyrifos, diazinon, and malathion [7, 8, 11]. Since electrospray ionization is a much softer ionization process than EI, the protonated molecular ion can be selected as the precursor ion for LC-ESI⁺-MS/MS and generally two fragments of significant abundance are observed such that two SRM transitions are available for quantitative and confirmation analysis (see Table 3). Organochlorines have poor sensitivity with LC-ESI⁺-MS/MS such that GC-MS methods are selected over LC-ESI⁺-MS/MS if organochlorines (OCs) are targeted along with OPs in a multiclass method (see Figure 1). However, LC-ESI⁺-MS/MS is also more amenable to a wider range of other pesticides included in multiclass methods, including azole fungicides, carbamates, phenylureas, and strobilurin fungicides (see Figure 1). Either chemical class-specific or multiclass separations can be achieved on reversed-phase stationary phases including C8, C12, C18, C6phenyl. OPs, OPoxons, OPsulfoxides, and OPsulfones observed better sensitivity with methanol rather than acetonitrile as the organic modifier in the mobile phase. Generally, ammonium acetate or ammonium formate is selected as an additive and pending the target list of OPs and their degradation products, 0.1% formic acid may also be added to the mobile phase to improve sensitivity. Only a few OP sulfones, sulfoxides, and oxons have been analyzed by GC-EI-MS/MS methods (Table 2) often due to the poor sensitivity, poor peak shapes, or poor chromatographic separation of these analytes due to their more polar nature such that LC-ESI⁺-MS/MS are preferred (see Table 4) [4, 6, 11, 19, 22–41].

OP	Organic modifier, additives in MP; column	SRM (quantitative, confirmation)	Ref
Acephate	MeOH, 10mM CH₃COONH₄; XTerra MS C18	182	[25]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	184→113, 184→95	[35]
	ACN, 0.1% HCOOH; C18	184→143	[4]
Azamethiphos	MeOH, 5 mM HCOONH₄; XDB-C18	325→183, 325→139	[23]
Azinphos-ethyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	346→160, 346→132	[11]
Azinphos-methyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	318→160, 318→132	[11]
	ACN, 0.1% HCOOH; C18	318→125, 318→132	[28]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	318→160, 318→132	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	318→132, 318→160	[37]
Chlorpyrifos-ethyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	352→97, 352→125	[11]
	MeOH, 5 mM HCOONH₄; XDB-C18	352→200, 352→97	[23]
	ACN, 0.1% HCOOH; C18	352→97, 352→200	[28]
	ACN, 20 mM CH₃COOH (pH 6.45-7.45); mixed mode RP/WAX	352→200, 352→115	[24]
	ACN, 0.025% HCOOH; Zorbax Extended C8	352→200	[29]
	ACN, 0.1% HCOOH; C18	350→198, 350→125, 352→200, 352→125	[30]
	ACN, 0.025% HCOOH; XDB-C8	352→200	[32]
	MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	350→198, 352→200	[33]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	350→198, 350→97	[35]
	MeOH, 20 mM CH₃COONH₄; C18	350→198, 350→294	[36]
	MeOH, 5 mM HCOONH₄; ODS-4	350→198, 350→97	[37]
	MeOH, 2 mM CH₃COONH₄; C18	350→198, 352→200	[38]
	ACN, 20 mM CH₃COONH₄, RP18	350→125, 352→198	[39]
	ACN, 0.1% HCOOH; C18	352→198	[4]
Chlorpyrifos-methyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	322→125, 324→125	[4]
	MeOH, 5 mM HCOONH4; XDB-C18	322→125, 322→290	[26]
	MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	322→125, 324→125	[36]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	322→125, 322→290	[38]
	MeOH, 5 mM HCOONH₄; ODS-4	322→125, 322→290	[40]
	ACN, 0.1% HCOOH; C18	322→290	[4]
Coumaphos	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	363→227, 363→307	[6]
	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	363→303, 363→289	[6]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	363→227, 363→307	[35]
Cyanophos	MeOH, 10mM CH₃COONH₄; XTerra MS C18	228	[25]
Demeton-S-methyl	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	231→89, 231→61	[6]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	231→89, 231→61	[35]
Diazinon	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	305→169, 305→153	[11]
	MeOH, 5 mM HCOONH₄; XDB-C18	305→169, 305→153	[23]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	305→169, 305→97	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	305→169, 305→153	[37]
	MeOH, 2 mM CH₃COONH₄; C18	305→169, 305→153	[38]
	ACN, 20 mM CH₃COONH₄, RP18	305→169, 305→153	[39]
	ACN, 0.1% HCOOH; C18	322→290	[4]
	ACN, 0.1% HCOOH; XDB-C18	305.103, 277.077, 249.047, 169.077, 153.102^*	[22]
	MeOH, 0.1 % HCOOH; X-Terra C18	305.1089→169.0799, 305.1089→153.1028*	[27]
Diazinon-d10 (IS)	MeOH, 0.1% HCOOH and 2 Mm CH₃COONH₄; C₆phenyl	315→170, 315→154	[11]
Dichlorvos	MeOH, 5 mM HCOONH4; XDB-C18	221→109, 221→127	[23]
	MeOH, 5 mM HCOONH₄; ODS-4	221→109, 221→127	[37]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	221→127, 221→109	[35]
	ACN, 0.1% HCOOH; C18	221→127	[4]
Dichlorvinphos	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	238→112, 238→193	[6]
Dicrotophos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	238→112, 238→127	[35]
Dimethoate	MeOH, 0.1% HCOOH and 2 Mm CH₃COONH₄; C₆phenyl	230→199, 230→125	[11]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	230→199, 230→125	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	230→199, 230→125	[37]
	MeOH, 2 mM CH₃COONH₄; C18	230→125, 230→143	[38]
	ACN, 0.1% HCOOH; C18	221→127	[4]
Disulfoton	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	275→89, 275→61	[35]
Ethion	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	385→199, 385→171	[35]
Ethoprofos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	243→131, 243→97	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	243→97, 243→131	[37]
Fenamiphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	304→217, 304→202	[35]
Fenchlorphos	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	321→125, 321→109	[11]
Fenitrothion	MeOH, 10mM CH₃COONH₄; XTerra MS C18	262	[25]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	278→125, 278→109	[35]
Fensulfothion	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	309→281, 309→157	[6]
Fenthion	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	279→169, 279→247	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	279→169, 279→247	[37]
	MeOH, 2 mM CH₃COONH₄; C18	279→169, 279→105	[38]
Malathion	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	331→127, 331→285	[11]
	MeOH, 10mM CH₃COONH₄; XTerra MS C18	315	[25]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	331→127, 331→99	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	331→127, 331→99	[37]
	ACN, 20 mM CH₃COONH₄, RP18	331→127, 331→285	[39]
Mevinphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	225→127, 225→193	[35]
Methamidophos	MeOH, 5 mM HCOONH4; XDB-C18	142→94, 142→125	[23]
Monocrotophos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	224→127, 224→98	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	331→127, 331→99	[37]
Naled	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	398→127, 398→109	[35]
Parathion-ethyl	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	292→236, 292→97	[35]
Parathion-methyl	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	264→125, 264→232	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	264→125, 264→109	[37]
Phorate	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	261→75, 261→47	[11]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	261→75, 261→171	[35]
Phosmet	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	318→160, 318→133	[35]
Pirimiphos methyl	MeOH, 5 mM HCOONH4; XDB-C18	306→164, 306→108	[23]
	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	306→164, 306→108	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	306→164, 306→108	[37]
Prothiophos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	345→241,345→133	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	345→241,345→133	[37]
Pyrazophos	MeOH, 5 mM HCOONH₄; ODS-4	374→222, 374→194	[37]
Quinalphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	299→163, 299→147	[35]
Tebufos	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	289→103, 289→57	[6]*
		289→57, 289→103	[35]
Temephos	ACN, CH₃COONH₄; C18	484, 523	[26]
Tetrachlorvinphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	367→127, 367→241	[35]
Triazophos	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	314→162, 314→119	[6]
		314→162, 314→119	[35]
Trichlorfon	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	274→109, 274→221	[35]
	MeOH, 5 mM HCOONH₄; ODS-4	257→109, 257→221	[37]

Table 3.

Selected ion monitoring (SIM) or selected reaction monitoring (SRM) transitions for organophosphorus pesticides (OPs) products by LC-ESI⁺-MS/MS methods.

^*

LC-ESI⁺-QTOF-MS.

An additional reason why LC-ESI⁺-MS/MS is chosen over GC-MS methods for OPs is the ability to analyze OPs and OP sulfones, sulfoxides, and oxons simultaneously with often comparable sensitivities to their parent OPs [6, 11, 26, 28, 29, 32, 35]. Molecular weight confirmation is available as the protonated molecular ion is high in abundance and generally selected for the precursor ion for LC-MS/MS (Table 3). Similar to the OPs, mobile phase containing methanol (and gradient elution) is often preferred for optimal sensitivity of OP degradation products. However, when OPs (or their degradation products) are included in multiclass methods, acetonitrile may be selected due to the sensitivity needs of other target chemical classes of pesticides and to reduce run times. Other degradation products including hydroxyl degrades of OPs and IMP can also be analyzed in positive ion mode by LC-ESI⁺(or APCI⁺)-MS/MS or LC-QTOF [11, 22, 27, 33, 40, 42].

Alkylphosphates and alkylthiophosphates can also be analyzed by LC-MS/MS but to achieve the required sensitivity LC-ESI^--MS/MS is selected such that they are typically analyzed in a separate method from OPs (see Table 4) [11, 24, 27, 31, 33, 34, 39]. To provide the best sensitivity, acetonitrile rather than methanol is selected as the organic modifier in the mobile phase with either acetic or formic acid as a mobile phase additive. Chlorpyrifos degradation product 3,5,6-trichloro-2-pyridinol has been widely studied and can be included in LC-ESI⁺-MS/MS methods with approximately a 50 times higher detection limit than OPoxons [11]. LC-ESI^--MS/MS has also been widely used, however, collision-induced dissociation only produces the Cl^- fragment ion such that it is more common to monitor the ³⁵Cl and ³⁷Cl isotopes peaks of the deprotonated molecular ion at 196→196 or 198→198 if included in SRM methods when concentrations are lower [23, 29, 30, 32, 40, 41].

OP	Parent	Organic modifier, additives; column	SRM (quantitative, confirmation)	Ref
Azinphos methyl oxon	Azinphos methyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	302→160, 302→132	[11]
		ACN, 0.1% HCOOH; C18	302→132, 302→245	[28]
Chlorpyrifos-methyl oxon	Chlorpyrifos-methyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	308→109, 306→109	[11]
Chlorpyrifos-ethyl oxon	Chlorpyrifos-ethyl	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	336→280, 336→200	[11]
		ACN, 0.1% HCOOH; C18	336→280, 336→308	[28]
		ACN, 0.025% HCOOH; Zorbax Extended C8	336→280	[29]
		ACN, 0.025% HCOOH; XDB-C8	336→280	[32]
Coumaphos oxon	coumaphos	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	347→291, 347→211	[11]
Demeton-S-methyl sulfone	Demeton-S-methyl	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	263→169, 263→121	[6]
		MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	263→169, 263→108	[35]
Dibutylphosphate (IS)		ACN, 20 mM CH₃COOH (pH 6.45-7.45); mixed mode RP/WAX	209→79, 209→153^ESI-	[24]
Diethyl phosphate	OP	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	155→99, 155→127	[11]
		ACN, 20 mM CH₃COOH (pH 6.45-7.45); mixed mode RP/WAX	153→79, 153→125^ESI-	[24]
		ACN, 0.1% HCOOH; MAXRP, RP12	153→125, 153→79^ESI-	[31]
		ACN, 1 mM tetrabutylammonium acetate; C18	153→79, 153→125, 153→63^ESI-	[34]
		MeOH, 0.1% HCOOH; X-Terra C18	153.0317→125.0004, 153.0317→78.9585^ESI-*	[27]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	153→79, 153→125^ESI-	[33]
Diethyldithiophosphate	OP	ACN, 1 mM tetrabutylammonium acetate; C18	185→111^ESI-	[31]
		ACN, 20 mM CH₃COONH₄, RP18	155→127, 155→99	[39]
Diethylthiophosphate	OP	ACN, 20 mM CH₃COOH (pH 6.45-7.45); RP/WAX	169→95, 169→141^ESI-	[24]
		ACN, 1 mM tetrabutylammonium acetate; C18	169→97, 169→141^ESI-	[31]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	169→95, 169→141^ESI-	[33]
		ACN, 0.1% HCOOH; MAXRP, C-12	169→95, 169→141, 169→63^ESI-	[34]
		MeOH, 0.1% HCOOH; X-Terra C18	169.0977→140.9775, 169.0977→94.9357^ESI-*	[27]
		ACN, 20 mM CH₃COONH₄, RP18	171→143, 171→115	[39]
Dimethylphosphate	OP	ACN, 1 mM tetrabutylammonium acetate; C18	125→63, 125→79^ESI-	[31]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	125→79, 125→63^ESI-	[33]
		ACN, 20 mM CH₃COONH₄, RP18	127→109, 129→95	[39]
Dimethylthiophoshate	OP	ACN, 1 mM tetrabutylammonium acetate; C18	141→126, 141→95^ESI-	[31]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	141→79, 141→63, 141→95^ESI-	[33]
		ACN, 20 mM CH₃COONH₄, RP18	143→125, 143→111	[39]
dimethyldithiophosphate	OP	ACN, 20 mM CH₃COONH₄, RP18	157→142, 157→112	[39]
Diazinon-oxon	diazinon	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	289→153, 289→93	[11]
		MeOH, 0.1% HCOOH; X-Terra C18	289.1317→153.1028, 289.1317→261.1004*	[27]
Disulfoton sulfone	disulfoton	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	307→97, 307→153	[6]
		MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	307→153, 307→171	[35]
Disulfoton sulfoxide	disulfoton	MeOH, 0.1% HCOOH; Acquity UPLC™BEH C18	291→185, 291→97	[6]
		MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	291→213, 291→185	[35]
Fenamiphos sulfone	fenamiphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	336→266, 336→308	[35]
Fenamiphos sulfoxide	fenamiphos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	320→171, 320→251	[35]
Fenchlorphos oxon	fenchlorphos	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	307→109, 305→109	[11]
Fenthion sulfone	fenthion	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	311→125, 311→279	[35]
Fenthion sulfoxide	fenthion	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	295→280, 295→127	[35]
5-hydroxydiazinon	diazinon	MeOH, 0.1% HCOOH; X-Terra C18	321.1038→293.0725, 321.1038→185.0749*	[27]
			319.0882→291.0568, 319.0882→229.0412^ESI-*
7(1-hydroxy isopropyl diazinon	diazinon	MeOH, 0.1% HCOOH; X-Terra C18	321.1038→303.0932, 321.1038→275.0619*	[27]
4(1-hydroxyisopropyl diazoxon	diazinon	MeOH, 0.1% HCOOH; X-Terra C18	305.1266→287.1161, 305.1266→277.0953*	[27]
2-(1-hydroxy-1-methylethyl)-6-methyl-4(1H)-pyrimidinone	diazinon	MeOH, 0.1% HCOOH; Zorbax SB-CN	169→84	[19]
2-isopropyl-6-methyl-4-pyrimidinol	diazinon	ACN, 0.1% HCOOH; XDB-C18	153.1022, 84.0444, 70.0651*	[22]
		MeOH, 0.1% HCOOH; X-Terra C18	153.1028→137.0715, 153.1028→84.0575, 151.0872→135.0558, 151.0872→123.0558^ESI-	[27]
isomalathion	malathion	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	331→99, 331→127	[11]
2-isopropyl-6-methyl-4-pyrimidinol (IMP)	diazinon	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	153→84, 153→70	[11]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	153→84, 153→70	[33]
		MeOH, 1% CH₃COOH; C18	153→84, 153→70	[40]
		ACN, 0.1% HCOOH; XDB-C18	153.1022, 84.0444, 70.0651*	[22]
Malathion monocarboxylic acid	malathion	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	303→127, 303→99	[11]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	301→142, 301→157	[33]
			301→126, 301→141
Malathion dicarboxylic acid	malathion	MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	273→141, 273→157	[33]
Malathion-oxon	malathion	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	315→127, 315→99	[11]
o-methoate	dimethoate	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	214→183, 214→125	[11]
		MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	214→125, 214→109	[35]
		MeOH, 5 mM HCOONH₄; ODS-4	214→125, 214→183	[37]
			214→183	[4]
6-methyl-2-(1-methylethyl)4(1H)-pyrimidinone	diazinon	MeOH, 0.1% HCOOH; Zorbax SB-CN	153→84	[19]
3-methyl4-nitrophenol	fenitrothion	MeOH, 10mM CH₃COONH₄; XTerra MS C18	152	[25]
Parathion methyl oxon	Parathion methyl	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	248→202, 248→109	[35]
Phorate oxon	phorate	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	245→75, 245→47	[11]
Phorate sulfone	phorate	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	293→171, 293→97	[35]
Phorate sulfoxide	phorate	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	277→199, 277→143	[35]
3,5,6-trichloro-2-pyridinol	chlorpyrifos	MeOH, 0.1% HCOOH and 2 mM CH₃COONH₄; C₆phenyl	198→107, 198→134	[11]
		ACN, 0.1% CH₃COOH; XDB-C18	198→198, 196→196^ESI-	[23]
		ACN, 20 mM CH3COOH (pH 6.45-7.45); RP/WAX	196→35, 198→35^ESI-	[24]
		ACN, 0.025% HCOOH; Zorbax Extended C8	198^ESI-	[29]
		ACN, 0.1% HCOOH; C18	196→196, 198→198, 200→200^ESI-	[30]
		ACN, 0.025% HCOOH; XDB-C8	198→198	[32]
		MeOH, 0.1% CH₃COOH; XSELECT™ CSH™C18	198→37, 198→35, 196→35 ^ESI-	[33]
		ACN, 0.1% HCOOH; MAXRP, RP12	196→35, 198→37, 198→35, ^ESI-	[34]
		MeOH, 1% CH₃COOH; C18	196→196, 198→198^ESI-	[40]
		MeOH, 1% CH₃COOH; PhenylC6	196→196, 198→198^ESI-	[41]
Temephos oxon	temephos	ACN, CH₃COONH₄; C18	468	[26]
Temephos sulfoxide	temephos	ACN, CH₃COONH₄; C18	482, 483, 500, 523	[26]
Terbufos sulfone	terbufos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	321→115, 321→171	[35]
Terbufos sulfoxide	terbufos	MeOH, 5 mM CH₃COONH₄; MAX RP, C-12	305→131, 305→159	[35]

Table 4.

Selected ion monitoring (SIM) or selected reaction monitoring (SRM) transitions for organophosphorus pesticides (OPs) metabolites or degradation products by LC-ESI⁺-MS/MS methods.

3. Carbamates and phenylureas

LC-ESI⁺-MS/MS can be used for the simultaneous analysis of carbamates (general structure R₁OCONR₂R₃), phenylureas, and selected degradation products (see Table 5 for target list). Few carbamates are still analyzed directly by GC-EI-MS or GC-EI-MS/MS in multiclass methods (primarily carbaryl, carbofuran, carbosulfan, EPTC, isoprocarb, pirimicarb) [3, 9, 42, 43]. To improve sensitivity and extend the range of carbamates amenable to GC-EI-MS methods derivatized prior to analysis with 9-xanthydol, trimethylphenylammonium hydroxide and trimethylsulfonium hydroxide or sodium hydride has been used [43–45]. Metabolites of carbofuran and carbaryl have been analyzed after derivatization using trifluoroacetic acid with trimethylamine to produce volatile derivatives that can be analyzed by GC-EI-MS [46]. Photodegradation products (phenols and para-hydroxybenzamides) of carbamates were analyzed directly by GC-EI-MS/MS method [47].

Table 5.

Carbamates, selected degradation products, and phenylureas.

LC-ESI⁺-MS/MS is more frequently chosen than GC-MS methods for the analysis of carbamates and phenylureas in chemical class-specific or multiclass methods [39, 48–58]. OPs, carbamates, and phenylureas have a wide range of polarities so they can elute over similar time periods when typical reversed-phase stationary phases are used; however, in general, phenylureas elute later than carbamates and within the time range for OPs and pyrethroid insecticides.

For LC-ESI⁺-MS/MS the precursor ion is generally selected as the protonated molecular ion [M+H]⁺ (see Table 6). Both methanol and acetonitrile have been used as the organic modifier in the mobile phase for the separation of carbamates and when both chemical classes are analyzed together; however, acetonitrile provides the best overall sensitivity. Sodium adducts of carbamates can also be observed with ESI⁺ and have been attributed to impurities in methanolic mobile phases or sodium from metal tubing [51]. Both 0.1% formic acid and 5 mM ammonium acetate should be added to the mobile phase to improve sensitivity and to provide for ammonium adduct [M+NH₄]⁺ formation for aldicarb, methiocarb sulfone, and oxamyl (see Table 6) [51, 53]. Ammonium acetate can also improve the peak shapes observed in the separation. Aldicarb sulfone and methiocarb sulfone observed both the protonated molecular ion and ammonium adduct under these conditions [53]. The addition of ammonium acetate to the mobile phase also minimizes sodium adduct formation which was observed in this work and others for aldicarb, aldicarb sulfone, aldicarb sulfoxide, 3-hydroxycarbofuran, siduron, and diuron [51]. The common, group-specific fragmentation pathway for N-methylcarbamates is the neutral loss of methyl isocyanate (CH₃-N=C=O), while for phenylureas, loss of the substituted aniline ring is common. For methomyl-oxime only one significant fragment ion was formed. The RSD of the ratio of areas SRM1/SRM2 was less than 20% for the majority of the compounds (see Table 6) and method detection limits are generally 1–5 μg/L. Methomyl-oxime and methiocarb sulfone are not as sensitive as other carbamates, with detection limits of 10 μg/L for the quantitative SRM transition. Siduron has two isomers which are partially resolved on the Fusion-RP column. Other carbamates and phenylureas that have been analyzed by LC-ESI⁺-MS/MS include bendiocarb (224→167, 224→109 or 224→81 and 202→145), ethiofencarb (226→164, 253→126), ethiofencarb sulfone (258→107, 258→201), fenobucarb (208→152, 404→372), isoprocarb (194→137, 222→165), propoxur (210→110, 210→168), and other phenylureas include chlorotoluron (213→168, 213→140), desmethylisoproturon (193→151, 193→94), diflubenzuron (311→158, 311→141), isoproturon (207→165, 207→72), forchlorfenuron (248→129, 248→155), lufenuron (512→158, 512→141), metobromuron (259→148, 259→170), pencyuron (329→125, 329→218), teflubenzuron (381→158, 381→141), and triflumuron (359→156, 359→139) [6, 39, 49, 50, 53, 56].

Atmospheric pressure chemical ionization in positive and negative modes (APCI⁺ or APCI^-) can give similar range of sensitivity and structural information as ESI⁺ and can provide added selectivity for the LC-MS/MS analysis of carbamates [51]. Sodium adducts of the molecular ion do not form with APCI⁺ and sensitivity is better in positive ion mode than in negative ion mode, partially due to greater fragmentation with to [M-CONHCH₃]⁻ in the APCI⁻ ion source [52, 59]. LC-APCI⁺-MS has also been found to be more sensitive for some phenylureas [60].

Compound (molecular weight)	Transitions	Cone voltage (V)	Collision energy (eV)	Ratio SRM1/SRM2 areas ± RSD	Retention time (min)
Aldicarb (190.27)	208→89	10	15	2.66 ± 12.5%	12.46
Aldicarb (190.27)	208→116	10	15	2.66 ± 12.5%	12.46
Aldicarb sulfone (222.26)	223→76	15	10	2.83 ± 35.9%	4.60
Aldicarb sulfone (222.26)	240→86	15	20	2.83 ± 35.9%	4.60
Aldicarb sulfoxide (206.26)	207→89	15	15	1.13 ± 17.7%	3.29
Aldicarb sulfoxide (206.26)	207→132	10	5	1.13 ± 17.7%	3.29
Aminocarb (208.26)	209→152	20	15	1.39 ± 4.72%	2.85
Aminocarb (208.26)	209→137	20	20	1.39 ± 4.72%	2.85
Carbaryl (201.22)	202→145	22	10	3.32 ± 14.2%	16.35
Carbaryl (201.22)	202→127	20	25	3.32 ± 14.2%	16.35
Carbofuran (221.25)	222→123	20	20	2.73 ± 34.5%	15.27
Carbofuran (221.25)	222→165	20	20	2.73 ± 34.5%	15.27
Carboxin (235.31)	236→143	25	15	3.08 ± 11.3%	16.35
Carboxin (235.31)	236→86	20	25	3.08 ± 11.3%	16.35
EPTC (189.32)	190→128	20	10	1.70 ± 20.5%	19.99
EPTC (189.32)	190→86	20	10	1.70 ± 20.5%	19.99
3-Hydroxycarbofuran (237.25)	238→163	20	10	3.03 ± 10.6%	8.92
3-Hydroxycarbofuran (237.25)	238→220	20	10	3.03 ± 10.6%	8.92
Methiocarb (225.31)	226→121	15	20	1.40 ± 11.4%	18.31
Methiocarb (225.31)	226→169	15	10	1.40 ± 11.4%	18.31
Methiocarb sulfone (257.31)	275→122	15	20	1.01 ± 2.10%	12.61
Methiocarb sulfone (257.31)	258→122	25	15	1.01 ± 2.10%	12.61
Methiocarb sulfoxide (241.31)	242→122	20	25	1.24 ± 9.46%	9.35
Methiocarb sulfoxide (241.31)	242→170	20	25	1.24 ± 9.46%	9.35
Methomyl (162.21)	163→88	10	10	1.63 ± 4.24%	5.48
Methomyl (162.21)	163→106	10	10	1.63 ± 4.24%	5.48
Methomyl-oxime (105.16)	106→58	15	10	1.00 ± 7.02%	3.23
Methomyl-oxime (105.16)	106→106	20	0.010	1.00 ± 7.02%	3.23
Oxamyl (219.36)	237→72	20	10	2.45 ± 35.9%	4.66
Oxamyl (219.36)	237→90	20	10	2.45 ± 35.9%	4.66
Oxamyl-oxime (162.21)	163→72	15	10	7.03 ± 27.7%	2.68
Oxamyl-oxime (162.21)	163→90	15	20	7.03 ± 27.7%	2.68
Pirimicarb (238.29)	239→72	25	20	2.51 ± 7.80%	8.35
Pirimicarb (238.29)	239→182	30	15	2.51 ± 7.80%	8.35
Propamocarb HCl (224.73)	189→102	30	10	7.49 ± 21.4%	2.90
Propamocarb HCl (224.73)	189→74	35	15	7.49 ± 21.4%	2.90
Thiodicarb (354.47)	355→163	15	10	2.06 ± 29.5%	15.63
Thiodicarb (354.47)	355→108	15	15	2.06 ± 29.5%	15.63
Diuron (233.10)	233→72	25	15	1.98 ± 23.1%	16.83
Diuron (233.10)	235→72	25	15	1.98 ± 23.1%	16.83
Linuron (249.09)	251→162	15	20	2.20 ± 30.5%	18.68
Linuron (249.09)	251→184	20	15	2.20 ± 30.5%	18.68
Neburon (275.18)	276→88	30	15	4.86 ± 15.0%	20.27
Neburon (275.18)	276→114	35	15	4.86 ± 15.0%	20.27
Siduron (232.32)	233→94	30	20	1.12 ± 6.70%	18.22
Siduron (232.32)	233→137	30	17	1.12 ± 6.70%	18.22
EPTC-d₁₄ (203.4)	204→50	20	20	N/A	19.99
Diuron-d₆ (239.13)	239→52	20	20	N/A	16.83

Table 6.

Selected reaction monitoring transitions, cone voltage, collision energy, and retention times for the selected carbamates, their degradation products, phenylureas.

Quantitative transitions, where applicable, are shown in bold.

LC-ESI⁺-MS/MS conditions: Synergi™ Fusion-RP, 60 mm × 2.0 mm i.d., 2.5 μm column; mobile phase of water/acetonitrile with 5 mM ammonium acetate and 0.1% formic acid in aqueous and 0.1% formic acid in organic modifier at a flow rate of 0.15 mL/min with organic modifier starting at 25% v/v and undergoing a gradient to 35% v/v over 4 min, followed by a series of gradient steps as follows: to 80% v/v from 4 to 14.5 min, held for 8 min, to 100% v/v from 22.5 to 23.5 min, and held for 25 min with column temperature at 22°C.

Some of the main degradation products analyzed by LC-ESI⁺-MS/MS are shown in Table 6 and include carbamate sulfone or sulfoxides and hydroxyl derivative. Metabolites of carbofuran and carbosulfan have also been analyzed using LC-turboIonSpray-MS/MS, LC-APCI⁺-MS and LC-QqTOF-MS/MS [61–66]. Other degradation products identified include 3-ketocarbofuran, 3-hydroxy-7-phenolcarbofuran, 3-keto-7-phenolcarbofuran, 7-phenolcarbofuran, and dibutyl amine.

LC-APCI ⁺-MS and LC-atmospheric pressure photoionization (APPI⁺)-MS have also been used to analyze these metabolites as well as sulfoxides and sulfones of carbamates with the protonated molecular ion, ammonium adduct, and [M+H-CH₃NCO]⁺ observed in the ion source [67–69].

4. Pyrethroid insecticides and their metabolites

Figure 3 shows the structures of the pyrethroid insecticides. They have been routinely analyzed with GC-EI/MS, GC-EI-MS/MS, or GC-NCI-MS methods (see Table 7) [3, 5, 6, 9, 10, 14, 42, 70–81]. For the diverse range of pyrethroids these methods are preferred over LC-MS/MS methods. Pyrethroid insecticides are also often analyzed simultaneously with OCs and OPs (either EI or NCI) and generally elute latter in the separation than OCs and OPs. Detection limits with GC-EI-MS for pyrethroids are often more than sufficient for routine analysis in the μg/L range [10].

Analyte	SIM or SRM (m/z)	Ref
Pyrethroid insecticides
Allethrin C₁₉H₂₆O₃	123, 136, 202	[70]
	167, 68^{NCI, CH4}	This work
Bifenthrin C₂₂H₂₂ClF₃O₂	181, 165	[5, 6]
	181, 105	[9]
	181→ 115, 181→165	[3]
	181, 165, 166	[79, 10]
	181→166, 181→165	[76]
	205, 241^{NCI, CH4}	[77], this work
	386, 387, 388^{NCI, CH4}	[10]
Cyfluthrin (4 peaks) C₂₂H₁₈Cl₂FNO₃	163, 226	[70]
	163, 127	[5]
	206, 150	[6]
	163→127, 226→206	[3]
	207, 209^{NCI, CH4 or NH3}	This work
λ-Cyhalothrin C₂₃H₁₉ClF₃NO₃	209, 181	[70]
	181, 127	[5]
	181, 152	[6]
	205→121, 241→205	[76]
	197→141, 197→161	[14]
	181→127, 197→161	[3]
	181→152, 197→141, 197→161	[80]
	205, 241^{NCI, NH3 or CH4}	[77], this work
Cypermethrin (4 peaks) C₂₂H₁₉Cl₂NO₃	163, 181	[70]
	181, 163, 209	[79]
	181, 127	[5]
	163, 127	[6]
	91, 163, 181	[42]
	163, 165, 181	[10]
	207, 171^{NCI, NH3}	[77]
	207, 209^{NCI, CH4}	This work
	207, 209, 171	[10]
	207→35, 209→35	[14]
	163→127, 181→127	[3]
	163→127, 165→127, 165→129	[80]
Deltamethrin (2 peaks)	253, 255	[70]
C₂₂H₁₉Br₂NO₃	253, 172	[14]
	93, 181, 253	[42]
	253, 172+174	[6]
	181, 253, 163, 165	[81]
	181, 253, 251	[10]
	172→93, 253→93	[3]
	253→172, 253→174	[80]
	79, 137^{NCI, NH3}	[77]
	79,81^{NCI, CH4}	This work
	297, 299, 79^{NCI, CH4}	[10]
Esfenvalerate (2 peaks) C₂₅H₂₂ClNO₃	419, 167, 181	[70]
	211, 167^NCI	[77]
	211, 213^NCI	This work
	225→119, 225→147	[3]
Fenpropathrin C₂₂H₂₃NO₃	181, 265	[70]
	141^NCI	[77], this work
Fenvalerate (2 peaks) C₂₂H₂₂ClNO₃	167, 125	[5]
	109, 127, 244	[42]
	211, 167^NCI	[77]
	211→167, 213→169	[14]
	225→119, 225→147	[3]
	167→125, 125→89, 125→99	[80]
τ-fluvalinate C₂₆H₂₂ClF₃N₂O₃	250, 55	[5]
	250, 206, 252	[79]
	250, 200+214	[6]
	294, 258^NCI	[77]
	294, 296^NCI	This work
	250→55, 250→200	[3]
Flucythrinate (2 peaks) C₂₆H₂₃F₂NO₄	199, 157	[5]
Imiprothrin	123, 318, 151	[70]
Cis/trans-permethrin (2 peaks) C₂₁H₂₀Cl₂O₃	183, 165	[6, 70, 78]
	183, 163	[5, 9]
	207, 171^NCI	[77]
	207, 209^NCI	This work
	207→35, 209→35	[14]
	163→127, 183→128	[3]
	163→127, 165→127	[80]
	165→129
Phenothrin C₂₃H₂₆O₃	183, 163	[70]
	331, 167^NCI	[77]
Prallethrin C₁₉H₂₄O₃	123, 300	[70]
	167, 132, 168	This work
Resmethrin (two peak) C₂₂H₂₆O₃	171, 123, 338	[70]
	337, 167^NCI	[77]
Tefluthrin C₁₇H₁₄ClF₇O₂	205, 241^NCI	This work
Tetramethrin (two peak) C₁₉H₂₅NO₄	164, 123	[70]
	164, 107	[5]
	349, 167^NCI	[77]
Tralomethrin C₂₂H₁₉Br₄NO₃	181, 253, 163, 165	[81]
	79, 137^NCI	[77]
Transfluthrin C₁₅H₁₂C_l2F₄O₂	163→121, 163→117	[3]
Metabolites (derivatization reagent)
CA (diazomethane)	182, 167, 123	[70]
CA (PFBBr)	295→79, 297→79	[14]
DBCA(diazomethane)	231, 233	[70]
DBCA (PFBBr)	312, 253, 231	[71]
DBCA (PFBBr)	295→79, 297→79	[14]
DBCA (MTBSTA)	355, 353, 357, 172	[73, 75]
DBCA (HFIP)	369	[74]
DCCA (diazomethane)	187, 189, 163	[70]
DCCA (PFBBr)	222, 187, 163	[71]
DCCA (PFBBr)	207→35, 209→35	[14]
DCCA (MTBSTA)	265, 267	[72, 75]
DCCA (MTBSTA)	265, 267, 128, 307	[73]
DCCA (HFIP)	323	[74]
3PBA (diazomethane)	197, 228	[70]
3PBA (PFBBr)	228, 197	[71]
3PBA (MTBSTFA)	271, 227, 197	[73, 75]
3PBA (HFIP)	364	[74]
4F3PBA (diazomethane)	246, 215	[70]
4F3PBA (PFBBr)	246, 215	[71]
4F3BA (MTBSTFA)	289, 245, 214	[73, 75]
FBAc(TMSI-TMCS)	251, 252	[72]
MCA(TMSI-TMCS)	211, 212	[72]
CH₃FBAc(TMSI-TMCS)	265, 266	[72]
FB-Al (TMSI-TMCS)	237, 238	[72]
CH3-FB-Al (TMSI-TMCS)	251, 252	[72]
CH₃OCH₂-FB-Al	281, 282	[72]
HOCH₂-FB-Al	339, 340	[72]

Table 7.

GC-MS or GC-MS/MS methods for pyrethroids and metabolites.

Electron ionization unless noted. Pentafluorobenzyl bromide, PFBBr; tert-butyldimethylsilyl derivatives of MTBSTFA; 1,1,1,3,3,3-hexafluoroisopropanol (HFIP); and N-trimethlsilylimidazole (TMSI)-trimethylchlorosilane (TMCS) for alcoholic metabolites.

Figure 3:
Structures of pyrethroid insecticides.

Negative chemical ionization can provide higher MS selectivity for halogenated pyrethroids compared to GC-EI-MS [7, 10]. Some studies have shown that ammonia, rather than methane, as the reagent gas yields lower detection limits for pyrethroids analyzed by GC-NCI-MS [74], however, methane is still preferred for analysis of OCs and OPs [7, 10]. Pyrethroids also easily fragment in the EI source such that the molecular ion has low abundance and fragment ions are selected for quantitation and confirmation as shown in Table 7. For GC-EI-MS/MS the precursor ion is selected as a fragment ion in order to obtain sufficient sensitivity and used over GC-EI-MS when added selectivity is required for more difficult sample matrices.

Metabolites of pyrethroids include the following: 3-(2,2-dimethylvinyl)-2,2-dimethylcyclopropane-1-carboxylic acid, CA (metabolite of allethrin, imiprothrin, phenothrin, prallethrin, resmethrin, and tetramethrin); 4-fluoro-3-phenoxybenzoic acid, 4-fluoro-3-phenoxybenzoic acid, 4FPBA (metabolite of cyfluthrin), cis- and trans-2,2-dichlorvinyl-2,2-dimethylcyclopropane-1-carboxylic acid, DCCA (metabolite of cyfluthrin, cypermethrin, and permethrin); and 3-phenoxybenzoic acid, 3-PBA (metabolite of cyhalothrin, cypermethrin, deltamethrin, esfenvalerate, fenpropathrin, phenothrin, and permethrin), cis-2,2-dibromovinyl-2,2-dimethyl-2,2-dimethylcyclopropane-1-carboxylic acid, DBCA (metabolite of deltamethrin). Additionally, both carboxylic acid and alcoholic derivatives can form fluoro-containing pyrethroids including the following: 2,3,5,6-tetrafluorobenzyl alcohol (FB-Al) and 2,3,5,6-tetraflurobenzoic acid (FB-Ac) (metabolites of transfluthrin); 2,3,5,6-tetrafluorobenzoic acid (CH₃-FB-Ac) and 4-methyl-2,3,5,6-tetrafluorobenzyl alcohol (CH₃-FB-Al) (metabolites of profluthrin); 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl alcohol (CH₃OCH₂-FB-Al) (metabolite of metofluthrin); and 4-hydroxymethyl-2,3,5,6-tetrafluorobenzyl alcohol (HOCH₂-FB-Al) (metabolite of metofluthrin and profluthrin) [72]. Most studies include cis/trans-DCCA, DBCA, 4F3PBA, and 3PBA in their analysis of metabolites of pyrethroids (see Table 7). Analysis of metabolites by GC-EI-MS requires derivatization of the metabolites prior to analysis with pentafluorobenzyl bromide (PFBBr), tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTMSTFA). or 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and N-trimethlsilylimidazole (TMSI)-trimethylchlorosilane (TMCS) for alcoholic metabolites [14, 70–75]. GC-EI-MS/MS has not been widely used for analysis of the metabolites. Derivatization extends the range of metabolites that are amenable to GC-EI-MS above those commonly analyzed by LC-MS/MS. Some metabolites of pyrethroids including DBCA, DCCA, 4FPBA, and 3PBA can be analyzed by LC-ESI^--MS/MS (see Table 8) [33, 41, 82–84]. Pyrethroids that ionize in an electrospray ion source are more sensitive in positive ion mode with the ammonium adduct formed such that ammonium acetate at ~5 mM should be added to the mobile phase. For those pyrethroids that are more sensitive with LC-ESI^--MS/MS (cyfluthrin and cyhalothrin), the deprotonated molecular ion forms in the ion source. The metabolites form the deprotonated molecular ion in the ESI ion source. In general, only a few pyrethroids have been included in LC-ESI⁺-MS/MS multiclass methods.

Analyte (monoisotopic mass)	SIM or SRM (m/z)	Reference
Pyrethroids
Bifenthrin (422.1)	440→182	[82]
Cyfluthrin (433.1)	451→191, 451→434	[39]
	435→191, 435→127	[84]
	432→405	[82]
Cyhalothrin (449.1)	448.2→402.8^ESI-	[82]
Cypermethrin (415.1)	433→191, 433→416	[35, 39, 84]
	433→191	[82]
Deltamethrin (502.0)	523→506, 523→281	[39]
	506→281, 506→253	[84]
	521→279	[82]
Permethrin (390.1)	408→355, 408→183	[84]
	408→183	[82]
Esfenvalerate (419)	437→167	[82]
Metabolites
DBCA	343→81, 297→81^ESI-	[83]
	295→79^ESI-	[82]
	299→299	[84]
DCCA	207→207, 209→209^ESI-	[41, 84]
	207→207, 207→35^ESI-	[39]
	207→35, 209→35, 209→37^ESI-	[33]
	209→37, 207→35^ESI-	[83]
	207→35^ESI-	[82]
4-FPBA	231→93, 231→65^ESI-	[83]
	231→93^ESI-	[82]
3-PBA	213→93, 213→169^ESI-	[33, 41]
	213→93, 213→65^ESI-	[83]
	213→93^ESI-	[82]

Table 8.

Pyrethroid insecticides and their metabolites by LC-MS/MS. Electrospray ionization in positive ion mode unless noted.

5. Other considerations

Generally, there is a larger diversity of azole fungicides and strobilurin fungicides that can be analyzed with LC-ESI⁺-MS/MS methods as compared to those amenable to GC-MS methods [76, 79, 80, 85, 86]. For pesticides that are halogenated, GC-NCI-MS should be considered as an option to improve the sensitivity or selectivity of the analysis. Dissociative electron capture is often observed in negative chemical ionization for OPs, OCs, pyrethroids, azole fungicides, and strobilurin fungicides. GC-EI-MS/MS methods may also provide added selectivity; however, as many pesticides from these chemical classes fragment easily in an EI ion source, the precursor ion may need to be selected as a fragment ion which is capable of undergoing further collision-induced dissociation to achieve the required sensitivity. OP metabolites (OP oxons, sulfones, sulfoxides, and selected others) can be analyzed by LC-ESI⁺-MS/MS, while alkylphosphates or alkylthiophosphates should be analyzed by LC-ESI ^--MS/MS or following derivatization by GC-MS. Pyrethroid metabolites are still commonly analyzed following derivatization with GC-EI-MS methods with a small selection of common pyrethroid metabolites also frequently analyzed by LC-MS/MS.

6. Conclusions

A larger number of OPs including organophosphates and organothiophosphates have been analyzed by GC-MS or GC-MS/MS methods as compared to LC-ESI⁺-MS/MS. GC-EI-MS or GC-EI-MS/MS is most commonly selected for analysis of OPs, and GC-EI-MS provides excellent confirmation of identity of the OP through spectral library matches. When added selectivity is required, such as when matrix remains after sample clean-up, analysis of OPs by GC-NCI-MS or GC-EI-MS/MS should be selected. GC-NCI-MS analysis of halogenated (or nitro substituted) OPs generally provides better sensitivity than GC-EI-MS/MS, particularly when the precursor ion selected for CID is the molecular ion. Although NCI is a softer ionization process than EI, fragment ions are still often observed as a result of dissociative electron capture. Sensitivity of GC-EI-MS/MS can be improved by selection of an abundant fragment ion for the precursor ion rather than the molecular ion which may be too low in abundance. The number of applications using LC-ESI⁺-MS/MS for the analysis of OPs has increased in the past ten years and for those OPs that can be ionized efficiently by ESI, the sensitivity may be better than with GC-MS methods (particularly for OPs that elute later in the GC separations). Another advantage of LC-ESI⁺-MS/MS is that it is feasible to analyze OP degradation products (OP oxons, OP sulfones, or OP sulfoxides) simultaneously with parent OPs. Derivatization of alkylphosphates and alkylthiophosphates metabolites of OPs is required to achieve the desired sensitivity when analyzed by GC-MS or GC-MS/MS methods. Alkylphosphate metabolites can also be analyzed by LC-ESI^--MS/MS.

Pyrethroids can be analyzed simultaneously with OCs and OPs using GC-EI-MS or GC-EI-MS/MS. A number of pyrethroids are halogenated and consequently they can be analyzed by GC-NCI-MS for added selectivity and sensitivity. Metabolites of pyrethroids are derivatized prior to the analysis by GC-EI-MS or GC-EI-MS/MS and this approach remains the method of choice for their analysis. Analysis of pyrethroids by LC-MS/MS is more limited; however, metabolites of pyrethroids can be analyzed using LC-ESI^--MS/MS.

Carbamates and phenylureas are commonly analyzed by LC-ESI⁺-MS/MS. Selected carbamates can be analyzed by GC-MS methods, but a derivatization step is required prior to analysis. The main degradation products of carbamates including carbamate sulfone or sulfoxides can be analyzed by LC-ESI⁺-MS/MS simultaneously with carbamates and phenylureas. APCI and APPI in positive ion mode have also been used to ionize metabolites of carbamates to achieve better sensitivity than ESI. APCI⁺ is also not prone to sodium adduct formation. Mobile phase additives used for the LC-ESI⁺-MS/MS separation of both OPs, carbamates and phenylureas include 0.1% formic acid and 5 mM ammonium acetate. Better sensitivity for OPs is obtained when methanol is used as the organic modifier for gradient elution, while acetonitrile is more commonly used for the separation of carbamates to obtain optimal sensitivity. Carbamates are prone to adduct formation (reduce sensitivity) in mobile phases containing methanol, and ammonium formate or ammonium acetate is generally used to reduce sodium adduct formation. Other pesticides that can be analyzed by LC-ESI⁺-MS/MS include azole fungicides, neonicotinoid insecticides, and strobilurin fungicides. Pending the target list of pesticides, it is feasible to obtain simultaneous analysis of all these chemical classes; however, if optimal sensitivity is required then class-specific methods will achieve better results.

Acknowledgments

This work was financially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada and additional instrument support from Canadian Foundation for Innovation.

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27. Ibanez, M.; Sancho, J.V.; Pozo, O.J.; Hernandez, F. (2006). Anal. Bioanal. Chem., 384, 448–457.
28. Armstrong, J.L.; Dills, R.L.; Yu, H.; Yost, M.G.; Fenske, R.A. (2014). J. Environ. Sci. Health, Part B, 49, 102–108.
29. Williamson, L.N.; Bartlett, M.G.; Terry, A.V. (2007). J. Liquid Chromatogr. Related Technol., 30, 273–285.
30. Sancho, J.V.; Pozo, O.J.; Hernandez, F. (2000). Rapid Commun. Mass Spectrom., 14, 1485–1490.
31. Hernandez, F.; Sancho, J.V.; Pozo, O.J. (2002). Rapid Commun. Mass Spectrom., 16, 1766–1773.
32. Williamson, L.N.; Terry, A.v.; Bartlett, M.G. (2006). Rapid Commun. Mass Spectrom., 20, 2689–2695.
33. Rousis, N.I.; Zuccato, E.; Castiglioni, S. (2016). Sci. Total Environ., 571, 1349–1357.
34. Bicker, W.; Lammerhofer, M.; Genser, D.; Kiss, H.; Lindner, W. (2005). Toxicol. Lett., 159, 235–251.
35. Chung, S.W.C.; Chan, B.T.P. (2010). J. Chromatogr. A, 1217, 4815–4824.
36. Liao, H.; Hsieh, C.; Chiang, S.; Lin, M.; Chen, P.; Wu, K. (2011). J. Chromatogr. A, 879, 1961–1966.
37. Golger, O.; Kabak, B. (2015). Food Chem., 176, 319–332.
38. Salm, P.; Taylor, P.J.; Roberts, D.; de Silva, J. (2009). J. Chromatogr. B, 877, 568–574.
39. Berton, T.; Mayhoub, F.; Chardon, K.; Duca, R.; Lestremau, F.; Bach, V.; Tack, K. (2014). Environ. Res., 132, 311–320.
40. Davis, M.D.; Wade, E.L.; Restrpo, P.R.; Roman-ESteva, W.; Bravo, R.; Kuklenyik, P.; Calafat, A.M. (2013). J. Chromatogr. B, 929, 18–26.
41. Radford, S.A.; Panuwet, P.; Hunter, R.E.; Barr, D.B.; Ryan, P.B. (2016). J. Agric. Food Chem., 64, 4633–4638.
42. Chowdhury, M.A.Z.; Fakhruddin, A.N.M.; Islam, N.; Moniruzzaman, M.; Gan, S.H.; Alam, K. (2013). Food Control, 34, 457–465.
43. Chen, H.; Chen, R.; Li, S. (2010). J. Chromatogr. A, 1217, 1244–1248.
44. Yang, E.; Shin, H. (2013). J. Chromatogr. A, 1305, 328–332.
45. Zhang, J.; Lee, H.K. (2006). J. Chromatogr. A, 1117, 31–37.
46. Crespo-Corral, E.; Santo-Delgado, M.J.; Polo-diez, L.M.; Sanz-Perucha, J. (2006). J. Chromatogr. A, 1132, 241–247.
47. Petropoulou, S.E.; Gikas, E.; Tsarbopoulos, A.; Siskos, P.A. (2006). J. Chromatogr. A, 1108, 99–110.
48. Climent, M.J.; Miranda, M.A. (1996). J. Chromatogr. A, 738, 225–231.
49. Choi, S.; Kim, S.; Shin, J.Y.; Kim, M.; Kim, J. (2015). Food Chem., 173, 1236–1242.
50. Nogueira, J.M.F.; Sandra, T.; Sandra, P. (2003). J. Chromatogr. A, 996, 133–140.
51. Pirard, C.; Widart, J.; Nguyen, B.K.; Deleuze, C.; Heudt, L.; Haubruge, E.; De Pauw, E.; Focant, J.-F. (2007). J. Chromatogr. A, 1152, 116–123.
52. Lee, S.J.; Park, S.; Choi, J.Y.; Shim, J.; Shin, E.; Choi, J.; Kim. S.T.; Abd El-Aty, A.M.; Jin, J.S.; Bae, D.W.; Shin, S.C. (2009). Biomed. Chromatogr., 23, 719–731.
53. Wang, J.; Cheung, W.; Grant, D. (2005). J. Agric. Food Chem., 53, 528–537.
54. Liu, M.; Hashi, Y.; Song, Y.; Lin, J. (2005). J. Chromatogr. A, 1097, 183–187.
55. Aguilera-Luiz, M.M.; Plaza-Bolanos, P.; Romero-Gonzalez, R.; Martinez Vidal, J.L.; Garrido Frenich, A. (2011). Anal. Bioanal. Chem., 399, 2863–2875.
56. Moreno-Gonalez, D.; Huertas-Perez, J.F.; Garcia-Campana, A.M.; Bosque-Sendra, J.M.; Gamiz-Gracia, L. (2013). J. Chromatogr. A, 1315, 1–7.
57. Zainudin, B.H.; Salleh, S.; Mohamed, R.; Yap, K.C.; Muhamad, H. (2015), Food Chem., 172, 585–595.
58. Shi, Z.; Hu, J.; Li, Q.; Zhang, S.; Liang, Y.; Zhang, H. (2014). J. Chromatgr. A, 1355, 219–227.
59. Fernandez, M.; Pico, Y.; Manes, J. (2000). J. Chromatogr. A, 871, 43–56.
60. Thurman, E.M.; Ferrer, I.; Barcelo, D. (2001). Anal. Chem., 73, 5441–5449.
61. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico, Y. (2007). Anal. Chem., 79, 1492–1501.
62. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico, Y. (2006). Anal. Chim. Acta, 571, 1–11.
63. Totti, S.; Fernandez, M.; Ghini, S.; Pico, Y.; Fini, F.; Manes, J.; Girotti, S. (2006). Talanta, 69, 724–729.
64. Abass, K.; Reponen, P.; Mattila, S.; Rautio, A.; Pelkonen, O. (2014). Toxicol. Lett., 224, 290–299.
65. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico Y. (2006). Rapid Commun. Mass Spectrom., 20, 2151–2164.
66. Detomaso, A.; Mascolo, G.; Lopez, A. (2005). Rapid Commun. Mass Spectrom., 19, 2193–2202.
67. Takino, M.; Yamaguchi, K.; Nakahara, T. (2004). J. Agric. Food Chem., 52, 727–735.
68. Nunes, G.S.; Alonso, R.M.; Ribeiro, M.L.; Barcelo, D. (2000). J. Chromatogr. A, 888, 113–120.
69. Soler, C.; Manes, J.; Pico, Y. (2006). J. Chromatogr. A, 1109, 228–241.
70. Starr, J.; Graham, S.; Stout, D.; Andrews, K.; Nishioka, M. (2008). Environ. Res., 108, 271–279.
71. Angerer, J.; Ritter, A. (1997). J. Chromatogr. B, 695, 217–226.
72. Yoshida, T. (2013). J. Chromatogr. B, 913, 77–83.
73. Schettgen, T.; Koch, H.M.; Drexler, H.; Angerer, J. (2002). J. Chromatogr. B, 778, 121–130.
74. Weilgomas, B.; Nahorski, W.; Czarnowski, W. (2013). Intern. J. Hyg. Environ. Health, 216, 295–300.
75. Wei, B.; Mohan, K.R.; Weisel, C.P. (2012). Intern. J. Hyg. Environ. Health, 215, 465–473.
76. Schummer, C.; Salquebre, G.; Briand, O.; Millet, M.; Appenzeller, B.M.R. (2012). Toxicol. Lett., 210, 203–210.
77. Feo, M.L.; Elijarrat, E.; Barcelo, D. (2010). J. Chromatogr. A, 1217, 2248–2253.
78. Pinheiro, A.S.; Rocha, G.O.; Andrade, J.B. (2011). Microchem. J., 99, 303–308.
79. Tankiewicz, M.; Morrison, C.; Biziuk, M. (2013). Talanta, 107, 1–10.
80. Salquebre, G.; Schummer, C.; Millet, M.; Briand, O.; Appenzeller, B.M.R. (2012). Anal. Chim. Acta, 710, 65–74.
81. Valverde, A.; Aguilera, A.; Rodriguez, M.; Boulaid, M. (2001). J. Chromatog. A, 943, 101–111.
82. Li, W.; Morgan, M.K.; Graham, S.E.; Starr, J.M. (2016). Talanta, 151, 42–50.
83. Le Grand, R.; Dulaurent, S.; J.M. Gaulier, J.M.; Saint-Marcoux, F.; Moesch, C.; Lachatre, G. (2012). Toxicol. Lett., 210, 248–253.
84. Meyer-Monath, M.; Chatellier, C.; Cabooter, D.; Rouget, F.; Morel, I.; Lestremau, F. (2015). Toxicol. Lett., 138, 231–239.
85. Raina, R.; Smith, E. (2012). J. AOAC Int., 95, 1350–1356.
86. Raina-Fulton, R. (2015). J. Agric. Food Chem., 63, 5152–5162.

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[26] 26. Lacorte, S.; Ehresmann, N.; Barcelo, D. (1996). Environ. Sci. Technol., 30, 917–923.

[27] 27. Ibanez, M.; Sancho, J.V.; Pozo, O.J.; Hernandez, F. (2006). Anal. Bioanal. Chem., 384, 448–457.

[28] 28. Armstrong, J.L.; Dills, R.L.; Yu, H.; Yost, M.G.; Fenske, R.A. (2014). J. Environ. Sci. Health, Part B, 49, 102–108.

[29] 29. Williamson, L.N.; Bartlett, M.G.; Terry, A.V. (2007). J. Liquid Chromatogr. Related Technol., 30, 273–285.

[30] 30. Sancho, J.V.; Pozo, O.J.; Hernandez, F. (2000). Rapid Commun. Mass Spectrom., 14, 1485–1490.

[31] 31. Hernandez, F.; Sancho, J.V.; Pozo, O.J. (2002). Rapid Commun. Mass Spectrom., 16, 1766–1773.

[32] 32. Williamson, L.N.; Terry, A.v.; Bartlett, M.G. (2006). Rapid Commun. Mass Spectrom., 20, 2689–2695.

[33] 33. Rousis, N.I.; Zuccato, E.; Castiglioni, S. (2016). Sci. Total Environ., 571, 1349–1357.

[34] 34. Bicker, W.; Lammerhofer, M.; Genser, D.; Kiss, H.; Lindner, W. (2005). Toxicol. Lett., 159, 235–251.

[35] 35. Chung, S.W.C.; Chan, B.T.P. (2010). J. Chromatogr. A, 1217, 4815–4824.

[36] 36. Liao, H.; Hsieh, C.; Chiang, S.; Lin, M.; Chen, P.; Wu, K. (2011). J. Chromatogr. A, 879, 1961–1966.

[37] 37. Golger, O.; Kabak, B. (2015). Food Chem., 176, 319–332.

[38] 38. Salm, P.; Taylor, P.J.; Roberts, D.; de Silva, J. (2009). J. Chromatogr. B, 877, 568–574.

[39] 39. Berton, T.; Mayhoub, F.; Chardon, K.; Duca, R.; Lestremau, F.; Bach, V.; Tack, K. (2014). Environ. Res., 132, 311–320.

[40] 40. Davis, M.D.; Wade, E.L.; Restrpo, P.R.; Roman-ESteva, W.; Bravo, R.; Kuklenyik, P.; Calafat, A.M. (2013). J. Chromatogr. B, 929, 18–26.

[41] 41. Radford, S.A.; Panuwet, P.; Hunter, R.E.; Barr, D.B.; Ryan, P.B. (2016). J. Agric. Food Chem., 64, 4633–4638.

[42] 42. Chowdhury, M.A.Z.; Fakhruddin, A.N.M.; Islam, N.; Moniruzzaman, M.; Gan, S.H.; Alam, K. (2013). Food Control, 34, 457–465.

[43] 43. Chen, H.; Chen, R.; Li, S. (2010). J. Chromatogr. A, 1217, 1244–1248.

[44] 44. Yang, E.; Shin, H. (2013). J. Chromatogr. A, 1305, 328–332.

[45] 45. Zhang, J.; Lee, H.K. (2006). J. Chromatogr. A, 1117, 31–37.

[46] 46. Crespo-Corral, E.; Santo-Delgado, M.J.; Polo-diez, L.M.; Sanz-Perucha, J. (2006). J. Chromatogr. A, 1132, 241–247.

[47] 47. Petropoulou, S.E.; Gikas, E.; Tsarbopoulos, A.; Siskos, P.A. (2006). J. Chromatogr. A, 1108, 99–110.

[48] 48. Climent, M.J.; Miranda, M.A. (1996). J. Chromatogr. A, 738, 225–231.

[49] 49. Choi, S.; Kim, S.; Shin, J.Y.; Kim, M.; Kim, J. (2015). Food Chem., 173, 1236–1242.

[50] 50. Nogueira, J.M.F.; Sandra, T.; Sandra, P. (2003). J. Chromatogr. A, 996, 133–140.

[51] 51. Pirard, C.; Widart, J.; Nguyen, B.K.; Deleuze, C.; Heudt, L.; Haubruge, E.; De Pauw, E.; Focant, J.-F. (2007). J. Chromatogr. A, 1152, 116–123.

[52] 52. Lee, S.J.; Park, S.; Choi, J.Y.; Shim, J.; Shin, E.; Choi, J.; Kim. S.T.; Abd El-Aty, A.M.; Jin, J.S.; Bae, D.W.; Shin, S.C. (2009). Biomed. Chromatogr., 23, 719–731.

[53] 53. Wang, J.; Cheung, W.; Grant, D. (2005). J. Agric. Food Chem., 53, 528–537.

[54] 54. Liu, M.; Hashi, Y.; Song, Y.; Lin, J. (2005). J. Chromatogr. A, 1097, 183–187.

[55] 55. Aguilera-Luiz, M.M.; Plaza-Bolanos, P.; Romero-Gonzalez, R.; Martinez Vidal, J.L.; Garrido Frenich, A. (2011). Anal. Bioanal. Chem., 399, 2863–2875.

[56] 56. Moreno-Gonalez, D.; Huertas-Perez, J.F.; Garcia-Campana, A.M.; Bosque-Sendra, J.M.; Gamiz-Gracia, L. (2013). J. Chromatogr. A, 1315, 1–7.

[57] 57. Zainudin, B.H.; Salleh, S.; Mohamed, R.; Yap, K.C.; Muhamad, H. (2015), Food Chem., 172, 585–595.

[58] 58. Shi, Z.; Hu, J.; Li, Q.; Zhang, S.; Liang, Y.; Zhang, H. (2014). J. Chromatgr. A, 1355, 219–227.

[59] 59. Fernandez, M.; Pico, Y.; Manes, J. (2000). J. Chromatogr. A, 871, 43–56.

[60] 60. Thurman, E.M.; Ferrer, I.; Barcelo, D. (2001). Anal. Chem., 73, 5441–5449.

[61] 61. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico, Y. (2007). Anal. Chem., 79, 1492–1501.

[62] 62. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico, Y. (2006). Anal. Chim. Acta, 571, 1–11.

[63] 63. Totti, S.; Fernandez, M.; Ghini, S.; Pico, Y.; Fini, F.; Manes, J.; Girotti, S. (2006). Talanta, 69, 724–729.

[64] 64. Abass, K.; Reponen, P.; Mattila, S.; Rautio, A.; Pelkonen, O. (2014). Toxicol. Lett., 224, 290–299.

[65] 65. Soler, C.; Hamilton, B.; Furey, A.; James, K.J.; Manes, J.; Pico Y. (2006). Rapid Commun. Mass Spectrom., 20, 2151–2164.

[66] 66. Detomaso, A.; Mascolo, G.; Lopez, A. (2005). Rapid Commun. Mass Spectrom., 19, 2193–2202.

[67] 67. Takino, M.; Yamaguchi, K.; Nakahara, T. (2004). J. Agric. Food Chem., 52, 727–735.

[68] 68. Nunes, G.S.; Alonso, R.M.; Ribeiro, M.L.; Barcelo, D. (2000). J. Chromatogr. A, 888, 113–120.

[69] 69. Soler, C.; Manes, J.; Pico, Y. (2006). J. Chromatogr. A, 1109, 228–241.

[70] 70. Starr, J.; Graham, S.; Stout, D.; Andrews, K.; Nishioka, M. (2008). Environ. Res., 108, 271–279.

[71] 71. Angerer, J.; Ritter, A. (1997). J. Chromatogr. B, 695, 217–226.

[72] 72. Yoshida, T. (2013). J. Chromatogr. B, 913, 77–83.

[73] 73. Schettgen, T.; Koch, H.M.; Drexler, H.; Angerer, J. (2002). J. Chromatogr. B, 778, 121–130.

[74] 74. Weilgomas, B.; Nahorski, W.; Czarnowski, W. (2013). Intern. J. Hyg. Environ. Health, 216, 295–300.

[75] 75. Wei, B.; Mohan, K.R.; Weisel, C.P. (2012). Intern. J. Hyg. Environ. Health, 215, 465–473.

[76] 76. Schummer, C.; Salquebre, G.; Briand, O.; Millet, M.; Appenzeller, B.M.R. (2012). Toxicol. Lett., 210, 203–210.

[77] 77. Feo, M.L.; Elijarrat, E.; Barcelo, D. (2010). J. Chromatogr. A, 1217, 2248–2253.

[78] 78. Pinheiro, A.S.; Rocha, G.O.; Andrade, J.B. (2011). Microchem. J., 99, 303–308.

[79] 79. Tankiewicz, M.; Morrison, C.; Biziuk, M. (2013). Talanta, 107, 1–10.

[80] 80. Salquebre, G.; Schummer, C.; Millet, M.; Briand, O.; Appenzeller, B.M.R. (2012). Anal. Chim. Acta, 710, 65–74.

[81] 81. Valverde, A.; Aguilera, A.; Rodriguez, M.; Boulaid, M. (2001). J. Chromatog. A, 943, 101–111.

[82] 82. Li, W.; Morgan, M.K.; Graham, S.E.; Starr, J.M. (2016). Talanta, 151, 42–50.

[83] 83. Le Grand, R.; Dulaurent, S.; J.M. Gaulier, J.M.; Saint-Marcoux, F.; Moesch, C.; Lachatre, G. (2012). Toxicol. Lett., 210, 248–253.

[84] 84. Meyer-Monath, M.; Chatellier, C.; Cabooter, D.; Rouget, F.; Morel, I.; Lestremau, F. (2015). Toxicol. Lett., 138, 231–239.

[85] 85. Raina, R.; Smith, E. (2012). J. AOAC Int., 95, 1350–1356.

[86] 86. Raina-Fulton, R. (2015). J. Agric. Food Chem., 63, 5152–5162.