Determination of pesticides in soil samples by supercritical fluid chromatography-atmospheric pressure chemical ionisation mass spectrometric detection

This paper presents an analytical technique for the determination of pesticides in soil by packed-column supercritical fluid chromatography interfaced with atmospheric pressure chemical ionisation mass spectrometry (pSFC-APCI-MS). The technique provides a versatile method for the detection and quantification of pesticides belonging to three different commonly used classes, triazines (ametryne, atrazine), carbamates (carbofuran) and sulfonylureas (chlorsulfuron, metsulfuron methyl and benzsulfuron methyl). The APCI mass spectra for all the pesticides studied consisted of protonated molecule ions as the most abundant ion at low cone voltages, except for metsulfuron methyl and benzsulfuron methyl, which gave a fragment ion as the most abundant ion with the protonated molecule ion at low intensity. Increasing the cone voltage provided informative fragmentation patterns for all species. The technique shows good linearity over the concentration range of 0.1-50 micrograms ml-1, with r2 values as follows: atrazine 0.997, ametryne 0.995, carbofuran 0.999, benzsulfuron methyl 0.999, chlorsulfuron 0.995 and metsulfuron methyl 0.997. The detection limits in the selected ion mode were atrazine 201, ametryne 144 and carbofuran 385 pg, which were calculated by using the standard solution, and benzsulfuron methyl 2.045, chlorsulfuron 1.435 and metsulfuron methyl 2.414 ng, which were determined by using spiked soil samples. The pSFC-MS system was shown to have a high degree of reproducibility. The technique was then applied to the determination of the above pesticides in soil samples. The results obtained show that there is no matrix effect from the soil and that the detection limits for all pesticides in soil were similar to those found for the standard solutions.     

Thermal desorption counter‐flow introduction atmospheric pressure chemical ionization for direct mass spectrometry of ecstasy tablets

A novel approach to the analysis of ecstasy tablets by direct mass spectrometry coupled with thermal desorption (TD) and counter‐flow introduction atmospheric pressure chemical ionization (CFI‐APCI) is described. Analytes were thermally desorbed with a metal block heater and introduced to a CFI‐APCI source with ambient air by a diaphragm pump. Water in the air was sufficient to act as the reactive reagent responsible for the generation of ions in the positive corona discharge. TD‐CFI‐APCI required neither a nebulizing gas nor solvent flow and the accompanying laborious optimizations. Ions generated were sent in the direction opposite to the air flow by an electric field and introduced into an ion trap mass spectrometer. The major ions corresponding to the protonated molecules ([M + H]⁺) were observed with several fragment ions in full scan mass spectrometry (MS) mode. Collision‐induced dissociation of protonated molecules gave characteristic product‐ion mass spectra and provided identification of the analytes within 5 s. The method required neither sample pretreatment nor a chromatographic separation step. The effectiveness of the combination of TD and CFI‐APCI was demonstrated by application to the direct mass spectrometric analysis of ecstasy tablets and legal pharmaceutical products. Copyright © 2009 John Wiley & Sons, Ltd.     

Dual parallel electrospray ionization and atmospheric pressure chemical ionization mass spectrometry (MS), MS/MS and MS/MS/MS for the analysis of triacylglycerols and triacylglycerol oxidation products

Two mass spectrometers, in parallel, were employed simultaneously for analysis of triacylglycerols in canola oil, for analysis of triolein oxidation products, and for analysis of triacylglycerol positional isomers separated using reversed-phase high-performance liquid chromatography. A triple quadrupole mass spectrometer was interfaced via an atmospheric pressure chemical ionization (APCI) interface to two reversed-phase liquid chromatographic columns in series. An ion trap mass spectrometer was coupled to the same two columns using an electrospray ionization (ESI) interface, with ammonium formate added as electrolyte. Electrospray ionization mass spectrometry (ESI-MS) under these conditions produced abundant ammonium adduct ions from triacylglycerols, which were then fragmented to produce MS/MS spectra and then fragmented further to produce MS/MS/MS spectra. ESI-MS/MS of the ammoniated adduct ions gave product ion mass spectra which were similar to mass spectra obtained by APCI-MS. ESI-MS/MS produced diacylglycerol fragment ions, and additional fragmentation (MS/MS/MS) produced [RCO](+) (acylium) ions, [RCOO+58](+) ions, and other related ions which allowed assignment of individual acyl chain identities. APCI-MS of triacylglycerol oxidation products produced spectra like those reported previously using APCI-MS. APCI-MS/MS produced ions related to individual fatty acid chains. ESI-MS of triacylglycerol oxidation products produced abundant ammonium adduct ions, even for those molecules which previously produced little or no intact molecular ions under APCI-MS conditions. Fragmentation (MS/MS) of the [M+NH(4)](+) ions produced results similar to those obtained by APCI-MS. Further fragmentation (MS/MS/MS) of the diacylglycerol fragments of oxidation products provided information on the oxidized individual fatty acyl chains. ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols.     

Mass spectrometric and tandem mass spectrometric behavior of nitrocatechol glucuronides: A comparison of atmospheric pressure chemical ionization and electrospray ionization

The mass spectrometric (MS) and tandem mass spectrometric (MS/MS) behavior of six nitrocatechol-type glucuronides using atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) was systematically studied, and the effect of operation parameters on the fragmentations are presented. The positive ion APCI- and ESI-MS spectra showed an intense protonated molecule and the respective negative ion spectra a deprotonated molecule with minimal fragmentation. The main fragment ions in the MS/MS spectra of the protonated and deprotonated molecules were [M + H - Glu]+ and [M - H - Glu]-, respectively, formed by the loss of the glucuronide moiety. The measured limits of detection indicated that ESI is a significantly more efficient ionization method than APCI in the negative and positive ion modes for the compounds studied. MS/MS was found to be less sensitive, but more reliable and simple than MS due to the absence of chemical noise.     

The even-electron rule in electrospray mass spectra of pesticides

A study of the fragmentation and ion formation of three major families of pesticides (including herbicides, insecticides, and fungicides) by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) and liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOF-MS) was carried out using positive electrospray ionization (ESI) and the results compared with those by gas chromatography (GC)/TOF-MS with electron ionization (EI) in order to test the validity of the even-electron rule in electrospray ionization. First, the majority of the fragmentations by positive ion ESI were even electron (EE) ions (93% of the fragment ions). Secondly, the formation of odd-electron (OE) fragment ions was greater with EI, where the fragment ions were present in a ratio of approximately 1:2 (35% OE ions and 65% EE ions). Thirdly, in-source collision-induced dissociation (CID) fragmentation by LC/TOF-MS and CID fragmentation in the collision cell by LC/Q-TOF-MS/MS resulted in 95% of the fragment ions being identical between the two types of fragmentation. As ESI in the positive ion mode yields an EE precursor ion (normally a protonated molecule), this commonly leads to EE fragment ions by elimination of molecules - a process called the even-electron rule. Neutral radical losses were less common in ESI but were common in the EI spectra of the same compounds. The structures that did lead to OE ions in ESI (exceptions to the even-electron rule approximately 7% of all ESI ions) favored electronegative radical losses in approximately the following order: .SO(2)CH(3), .NO(2), .CH(3), .Cl, .SCH(3), .CH(2)CH, and .OH.     

Analysis of tetrapyrrolic pigments and derivatives in sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A new application is described of the on-line high-performance liquid chromatography/positive and negative ion atmospheric pressure chemical ionization mass spectrometry (APCI(+/–)-MS) to the identification of tetrapyrrolic compounds in sediment samples containing complex mixtures of natural pigments and their diagenetic products. The method relies on the production of radical anions in order to determine the molecular masses of the molecules which yield abundant fragment ions when analyzed in the positive mode. This approach allows to verify the occurrence of coeluting components by examining their negative ion spectra and to complete their identification on the basis of their fragment ions produced in the positive ion spectra. Received: 24 September 1998 / Revised: 23 December 1998 / Accepted: 29 December 1998     

Analysis of tetrapyrrolic pigments and derivatives in sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A new application is described of the on-line high-performance liquid chromatography/positive and negative ion atmospheric pressure chemical ionization mass spectrometry (APCI(+/–)-MS) to the identification of tetrapyrrolic compounds in sediment samples containing complex mixtures of natural pigments and their diagenetic products. The method relies on the production of radical anions in order to determine the molecular masses of the molecules which yield abundant fragment ions when analyzed in the positive mode. This approach allows to verify the occurrence of coeluting components by examining their negative ion spectra and to complete their identification on the basis of their fragment ions produced in the positive ion spectra. Received: 24 September 1998 / Revised: 23 December 1998 / Accepted: 29 December 1998     

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

The effects of three additives—ammonium acetate, ammonium formate, and nicotinic acid—to the liquid chromatographic (LC) eluent and of the vaporizer temperature on the ion formation of N-methyl carbamate pesticides in thermospray (TSP) mass spectrometry was investigated by using filament- or discharge-assisted ionization. Nineteen carbamates and 12 of their known environmental degradation products were used as model compounds. The additives cause a strong reduction in the abundance of the characteristic fragment ions [M + H ? CH₃NCO]⁺ and [M ? H ? CH₃NCO]^? for some of the carbamates. The addition of nicotinic acid reduces the quasimolecular ion intensity and, in most cases, produces nicotinic acid adduct ions. The addition of ammonium acetate or ammonium formate increases the intensity of the quasimolecular ion and in most cases produces a base peak for the ammonium adduct ion. The combination of a suppression of fragmentation and an enhancement of quasimolecular ion formation produces an overall gain in sensitivity. As to more specific effects, the addition of the ammonium salts reduces the intensity of M^?? with the chlorinated carbamate barban and suppresses the formation of “odd” adduct ions in the TSP mass spectra of most other carbamates. Monitoring the intensity of the fragment and the quasimolecular ion signal as a function of the probe stem temperature, and the related probe tip temperature, proved to be an easy method to study the thermal degradation of the carbamates. This monitoring procedure showed that methiocarb and its sulfone already suffer from thermal degradation at a stem temperature of 90°C and that these compounds will therefore present problems in quantitation with LC/TSP mass spectrometry.     

Elucidation of the complex molecular structure of wheat straw lignin polymer by atmospheric pressure photoionization quadrupole time-of-flight tandem mass spectrometry

Wheat straw lignin was extracted using the novel CIMV procedure which selectively separates the cellulose, hemicelluloses and lignin. Solid-state (13)C NMR experiments using cross polarization/magic angle spinning (CP/MAS) were carried out on the extracted wheat straw lignin and some structural indices were revealed. Atmospheric pressure photoionization mass spectrometry (APPI-MS) has proven to be a powerful analytical tool capable of ionizing small to large lignin oligomers, which cannot be ionized efficiently by atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The APPI mass spectra of the extracted wheat straw lignin were recorded in the positive and negative ion modes. Positive ion mode APPI-MS indicated the exact presence of 39 specific oligomeric ions. Negative ion APPI-MS indicated the additional presence of at least 18 specific oligomeric ions. The structural characterization of this novel and complete series of 57 specific related oligomers was achieved by calculating the exact molecular masses measured by high-resolution quadrupole time-of-flight mass spectrometry (QqToF-MS). Some oligomeric species photoionized in both the positive and negative ion modes to form the respective protonated and deprotonated molecules. Low-energy collision-induced dissociation tandem mass spectrometric analyses performed with a QqToF-MS/MS hybrid instrument provided unique dissociation patterns of the complete series of novel precursor ions. These MS/MS analyses provided diagnostic product ions, which enabled us to determine the exact molecular structures and arrangement of the selected 57 different related ionic species.     

Chemical ionization and electron impact mass spectra of alicyclic substituted 2-aryl-1,3-dithianes

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2-aryl-1,3-dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.     

Atmospheric pressure ionization mass spectrometry techniques for the analysis of alkyl ethoxysulfate mixtures

This paper compares two liquid introduction atmospheric pressure ionization techniques for the analysis of alkyl ethoxysulfate (AES) anionic surfactant mixtures by mass spectrometry, i. e., electrospray ionization (ESI) in both positive and negative ion modes and atmospheric pressure chemical ionization (APCI) in positive ion mode, using a triple quadrupole mass spectrometer. Two ions are observed in ESI(+) for each individual AES component, [M + Na]⁺ and a “desulfated” ion [M − SO₃ + H]⁺, whereas only one ion, [M − Na]⁻ is observed for each AES component in ESI(−). APCI(+) produces a protonated, “desulfated” ion of the form [M − NaSO₃ + 2H]⁺ for each AES species in the mixture under low cone voltage (10 V) conditions. The mass spectral ion intensities of the individual AES components in either the series from ESI(+) or APCI(+) can be used to obtain an estimate of their relative concentrations in the mixture and of the average ethoxylate (EO) number of the sample. The precursor ions produced by either ESI(+) or ESI(−), when subjected to low-energy (50 eV) collision-induced dissociation, do not fragment to give ions that provide much structural information. The protonated, desulfated ions produced by APCI(+) form fragment ions which reveal structural information about the precursor ions, including alkyl chain length and EO number, under similar conditions. APCI(+) is less susceptible to matrix effects for quantitative work than ESI(+). Thus APCI(+) provides an additional tool for the analysis of anionic surfactants such as AES, especially in complex mixtures where tandem mass spectrometry is required for the identification of the individual components.     

Mass spectral fragmentation reactions of a therapeutic 4-azasteroid and related compounds

Mass spectra were acquired for a therapeutic 4-azasteroid (dutasteride), and some related compounds, using various ionization conditions (EI, CI, APCI and ESI) in both positive and negative ion modes. The ionization and fragmentation behavior of the compound dutasteride, its precursors and several analogs is reported. Positive atmospheric pressure chemical ionization (APCI+) and positive electrospray ionization (ESI+) produced distinctive collision-induced dissociation (CID) spectra for the respective [MH]+ ions of dutasteride. The spectral differences are attributed to ion populations having either different structures or different internal energy distributions (as a consequence of the method of ionization). Irrespective of their origin, the protonated molecules undergo interesting fragmentation reactions when collisionally activated. The identity of the major fragmentation products was confirmed by accurate mass measurement. The negative APCI mass spectrum of dutasteride displays extensive dehydrohalogenation, apparently due to the thermal component of the APCI process. Some of the resulting radical anions display remarkable stability toward collisional decomposition. Details of the fragmentation behavior for the negative ion species and their relationship to the positive ion results are discussed.     

A tandem mass spectrometric study of the N-oxides, quinoline N-oxide, carbadox, and olaquindox, carried out at high mass accuracy using electrospray ionization

A mass spectrometric study of three N-oxides, quinoline N-oxide, and the synthetic antibiotics carbadox and olaquindox, was carried out with a hybrid quadrupole/time-of-flight (TOF) mass spectrometer coupled with electrospray (ES) and atmospheric pressure chemical ionization (APCI) sources. The full scan mass spectra of the N-oxides obtained with ES are similar to those obtained with APCI, and the characteristic fragment ions corresponding to [M+H−O]⁺√ were observed in the full scan mass spectrum of each N-oxide examined. The protonated molecule of each N-oxide was subjected to collision-induced dissociation (CID) and accurate mass measurements were made of each fragment ion so as to determine its elemental composition. Fragment ions generated at enhanced cone voltages upstream of the first mass-resolving element were subjected to CID so as to identify the direct product ion–precursor ion relationship. Plausible structures have been proposed for most of the fragment ions observed. Elimination of OH√ radicals generated from the N→O functional group is a characteristic fragmentation pathway of the N-oxides. The expulsion of radicals and small stable molecules is accompanied by formation and subsequent contraction of heterocyclic rings.     

Liquid chromatography with dual parallel mass spectrometry and (31)P nuclear magnetic resonance spectroscopy for analysis of sphingomyelin and dihydrosphingomyelin. I. Bovine brain and chicken egg yolk

Liquid chromatography coupled to atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) mass spectrometry (MS), in parallel, was used for detection of bovine brain and chicken egg sphingolipids (SLs). APCI-MS mass spectra exhibited mostly ceramide-like fragment ions, [Cer-H(2)O+H](+) and [Cer-2H(2)O+H](+), whereas ESI-MS produced mostly intact protonated molecules, [M+H](+). APCI-MS/MS and MS(3) were used to differentiate between isobaric SLs. APCI-MS/MS mass spectra exhibited long-chain base related fragments, [LCB](+) and [LCB-H(2)O](+), that allowed the sphinganine backbone to be differentiated from the sphingenine backbone. Fragments formed from the fatty amide chain, [FA(long)](+) and [FA(short)](+), allowed an overall fatty acid composition to be determined. The presence of both dihydrosphingomyelin (DSM) and sphingomyelin (SM) sphingolipid classes was confirmed using (31)P NMR spectroscopy.     

Characterization of triglycerides in vegetable oils by silver-ion packed-column supercritical fluid chromatography coupled to mass spectroscopy with atmospheric pressure chemical ionization and coordination ion spray

Characterization of triglycerides in vegetable oils was achieved by silver-ion packed-column supercritical fluid chromatography (SI-pSFC) with mass spectrometric detection. Hyphenation was made using commercially available liquid chromatography-mass spectrometry (LC-MS) interfaces without any modification. A make-up fluid was delivered through a T-piece placed before or after the SFC restrictor by means of a high pressure pump. Atmospheric pressure chemical ionization (APCI) and coordination ion spray (CIS) with silver ions were used as ionization modes. Compared to UV detection, the sensitivity was increased by a factor of 100. Both ionization modes are generating similar structural information. Molecular ions [M-H]+ or [M-Ag(-)] are observed in the mass spectra with exception of the saturated triglycerides for which only CIS gives intense molecular ions. The position at which the fatty acids are esterified to the glycerol backbone can be elucidated by pSFC-APCI although it remains speculative whether this is valid for highly unsaturated triglycerides because reference compounds are not available to proof this.     

Mass spectral behavior of the hydrolysis products of sesqui- and oxy-mustard type chemical warfare agents in atmospheric pressure chemical ionization

Bis(2-hydroxyethylthio)alkanes and bis(2-hydroxyethylthioalkyl)ethers are important biological and environmental degradation products of sulfur mustard analogs known as sesqui- and oxy-mustards. We used atmospheric pressure chemical ionization mass spectrometry (APCI MS) to acquire characteristic spectra of these compounds in positive and negative ionization modes. Positive APCI mass spectra exhibited [M + H](+); negative APCI MS generated [M + O(2)](-), [M - H](-), and [M - 3H](-); and both positive and negative APCI mass spectra contained fragment ions due to in-source collision-induced dissociation. Product ion scans confirmed the origin of fragment ions observed in single-stage MS. Although the spectra of these compounds were very similar, positive and negative APCI mass spectra of the oxy-mustard hydrolysis product, bis(2-hydroxyethylthiomethyl)ether, differed from the spectra of the other compounds in a manner that suggested a rearrangement to the sesqui-mustard hydrolysis product, bis(2-hydroxyethylthio)methane. We evaluated the [M + O(2)](-) adduct ion for quantification via liquid chromatography-MS/MS in the multiple-reaction monitoring (MRM) mode by constructing calibration curves from three precursor/product ion transitions for all the analytes. Analytical figures of merit generated from the calibration curves indicated the stability and suitability of these transitions for quantification at concentrations in the low ng/mL range. Thus, we are the first to propose a quantitative method predicated on the measurement of product ions generated from the superoxide adduct anion of the sesqui-and oxy-mustard hydrolysis products.     

Chemical ionization and electron impact mass spectrometry of some organophosphonate compounds

The application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]₊ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.     

Cluster chemical ionization for improved confidence level in sample identification by gas chromatography/mass spectrometry

Upon the supersonic expansion of helium mixed with vapor from an organic solvent (e.g. methanol), various clusters of the solvent with the sample molecules can be formed. As a result of 70 eV electron ionization of these clusters, cluster chemical ionization (cluster CI) mass spectra are obtained. These spectra are characterized by the combination of EI mass spectra of vibrationally cold molecules in the supersonic molecular beam (cold EI) with CI-like appearance of abundant protonated molecules, together with satellite peaks corresponding to protonated or non-protonated clusters of sample compounds with 1-3 solvent molecules. Like CI, cluster CI preferably occurs for polar compounds with high proton affinity. However, in contrast to conventional CI, for non-polar compounds or those with reduced proton affinity the cluster CI mass spectrum converges to that of cold EI. The appearance of a protonated molecule and its solvent cluster peaks, plus the lack of protonation and cluster satellites for prominent EI fragments, enable the unambiguous identification of the molecular ion. In turn, the insertion of the proper molecular ion into the NIST library search of the cold EI mass spectra eliminates those candidates with incorrect molecular mass and thus significantly increases the confidence level in sample identification. Furthermore, molecular mass identification is of prime importance for the analysis of unknown compounds that are absent in the library. Examples are given with emphasis on the cluster CI analysis of carbamate pesticides, high explosives and unknown samples, to demonstrate the usefulness of Supersonic GC/MS (GC/MS with supersonic molecular beam) in the analysis of these thermally labile compounds. Cluster CI is shown to be a practical ionization method, due to its ease-of-use and fast instrumental conversion between EI and cluster CI, which involves the opening of only one valve located at the make-up gas path. The ease-of-use of cluster CI is analogous to that of liquid CI in ion traps with internal ionization, and is in marked contrast to that of CI with most other standard GC/MS systems that require a change of the ion source.     

Charge remote fragmentation of peptides following attachment of a fixed positive charge: A matrix-assisted laser desorption/ionization postsource decay study

A fixed positive charge can be placed at the N-terminus of a peptide by addition of a tris[(2,4,6-trimethoxyphenyl)phosphonium]acetyl group. The usefulness of these charged derivatives has been demonstrated in fast atom bombardment mass spectrometry and in matrix-assisted laser desorption/ionization mass spectrometry. After ion formation and acceleration, these derivatized peptide ions dissociate and their fragment ions can be analyzed in a postsource decay experiment by using a time-of-flight mass spectrometer. The matrix-assisted laser desorption/ionization-postsource decay spectra are very different from what may be expected based on fragment ions observed from protonated peptide molecules. Cleavage of CHR-C(O) bonds dominates to form a series of a type ions. Mechanistic possibilities are evaluated. When aspartic acid residues are encountered, the chemistry radically changes. This appears to be due to the formation of geometrically accessible intermediates that can dissociate via low energy processes. This chargeremote chemistry parallels that for much simpler systems, resulting in spectra that are very easy to interpret.     

Group-specific fragmentation of pesticides and related compounds in liquid chromatography–tandem mass spectrometry

Current strategies in the LC–MS analysis of pesticides and related compounds in environmental samples, fruits and vegetables, and biological samples mostly rely on the selection of appropriate precursor/product-ion combinations (transitions) for selected reaction monitoring (SRM), often based on automated parameter optimization and selection of the transition. Such a procedure does not require any information on the type of fragmentation reaction involved in the generation of the product ion from the selected precursor ion. However, such information does become important in untargeted screening for unknown contaminants in environmental and food samples, which are generally based on a combination of high-resolution mass spectrometry and (multistage) tandem mass spectrometry. With this in mind, the group-specific fragmentation behaviour has been studied for six classes of pesticides and herbicides, i.e., triazines, organophosphorous pesticides, phenylurea herbicides, carbamates, sulfonylurea herbicides, and chlorinated phenoxy acid herbicides. When relevant, some comparison was made between fragmentation of protonated molecules in MS–MS and of molecular ions generated by electron ionization in GC–MS.