Structural elucidation of disinfection by-products in treated drinking water

Two unusual disinfection by-products have been detected periodically in the gas chromatography/mass spectrometry (GC/MS) characterization analyses of semi-volatile organics in treated drinking water. The electron ionization (EI) mass spectra contained mono-chlorinated and mono-brominated ions at m/z 107/109 and 151/153, respectively. Library searching techniques suggested mono-halogenated butanol structures but no matches could be found. Positive ion chemical ionization (CI) spectra contained mono-chlorinated and mono-brominated ions at m/z 105/107 and 149/151, respectively. No [M + H]+ ions were initially observed. Accurate mass measurements confirmed the empirical formulae for the significant ions in the EI spectra and the mono-halogenated butanol structures. Further CI experiments with other reagent gases and instruments revealed possible molecular weights of 139 and 183 Da, respectively. Tandem mass spectrometry (MS/MS) experiments in EI and CI were used to elucidate the fragmentation schemes. The two compounds have been tentatively identified as 1-aminoxy-1-chlorobutan-2-ol and 1-aminoxy-1-bromobutan-2-ol, respectively.     

Positional isomer differentiation of synthetic cannabinoid JWH‐081 by GC‐MS/MS

Like many new designer drugs of abuse, synthetic cannabinoids (SC) have structural or positional isomers which may or may not all be regulated under law. Differences in acute toxicity may exist between isomers which impose further burden in the fields of forensic toxicology, medicine and legislation. Isomer differentiation therefore becomes crucial from these standpoints as new designer drugs continuously emerge with just minor positional modifications to their preexisting analogs. The aim of this study was to differentiate the positional isomers of JWH‐081. Purchased standard compounds of JWH‐081 and its positional isomers were analyzed by gas chromatography‐electron ionization‐mass spectrometry (GC‐EI‐MS) first in scan mode to investigate those isomers who could be differentiated by EI scan spectra. Isomers with identical or near‐identical EI spectra were further subjected to GC‐tandem mass spectrometry (MS/MS) analysis with appropriate precursor ions. EI scan was able to distinguish 3 of the 7 isomers: 2‐methoxy, 7‐methoxy and 8‐methoxy. The remaining isomers exhibited near‐identical spectra; hence, MS/MS was performed by selecting m/z 185 and 157 as precursor ions. 3‐Methoxy and 5‐methoxy isomers produced characteristic product ions that enabled the differentiation between them. Product ion spectrum of 6‐methoxy isomer resembled that of JWH‐081; however, the relative ion intensities were clearly different from one another. The combination of EI scan and MS/MS allowed for the regioisomeric differentiation of the targeted compounds in this study. Copyright © 2015 John Wiley & Sons, Ltd.     

Nitramine anion fragmentation: A mass spectrometric and Ab initio study

The fragment ion formation characteristics of the radical anions generated from hexahydro-1,3,5-trinitrotriazine (RDX) and its three nitroso metabolites were studied using GC/MS with negative chemical ionization (NCI) to understand the fragmentation mechanisms responsible for the formation of the most abundant ions observed in their NCI mass spectra. Ab initio and density functional theory calculations were used to calculate relative free energies for different fragment ion structures suggested by the m/z values of the most abundant ions observed in the NCI mass spectra. The NCI mass spectra of the four nitramines are dominated by ions formed by the cleavage of nitrogen-nitrogen and carbon-nitrogen bonds in the atrazine ring. The most abundant anions in the NCI mass spectra of these nitramines have the general formulas C(2)H(4)N(3)O (m/z 86) and C(2)H(4)N(3)O(2) (m/z 102). The analyses of isotope-labeled standards indicate that these two ions are formed by neutral losses that include two exocylic nitrogens and one atrazine ring nitrogen. Our calculations and observations of the nitramine mass spectra suggest that the m/z 86 and m/z 102 ions are formed from either the (M--NO)(-) or (M--NO(2))(-) fragment anions by a single fragmentation reaction producing neutral losses of CH(2)N(2)O or CH(2)N(2)O(2) rather than a set of sequential reactions involving neutral losses of HNO(2) or HNO and HCN.     

Fragmentation of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones under electron ionization

A series of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones was prepared, and the details of their fragmentation under electron ionization (EI) were elucidated. The molecular ions of each compound under consideration were quite abundant in their EI spectra. Full-scan spectra exhibited a number of fragment ions which were clearly assigned using MS/MS and accurate mass measurements. The basic fragmentation of 3,7-dialkyl-1,5-diphenylbispidinones was due to the cleavage of C(1)-C(2) bond followed by a hydrogen migration similar to an odd-electron McLafferty rearrangement. Alternatively, the C(1)-C(2) bond cleavage was followed by the elimination of an imine molecule, Alk-N=CH(2). Further fragmentation resulted in ions at m/z 234 and 103, present in the spectra of all the compounds under study. The fragmentation pathways proposed in this paper are based on the substituent shifts, accurate mass measurements and collision-induced dissociation spectra of selected ions. The results of the present work can be useful in selecting the fragment ions suitable for identification and quantitation of bispidinones in biological matrices.     

Detection and characterization by mass spectrometry of radical adducts produced by linoleic acid oxidation

The formation of linoleic acid radical species under the oxidative conditions of the Fenton reaction (using hydrogen peroxide and Fe (II)) was monitored by FAB-MS and ES-MS using the spin trap 5,5-dimethyl-1-pyrrolidine-N-oxide, DMPO. Both the FAB and ES mass spectra were very similar and showed the presence of ions corresponding to carbon- and oxygen centered spin adducts (DMPO/L*, DMPO/LO*, and DMPO/LOO*). Cyclic structures, formed between the DMPO oxygen and the neighboring carbon of the fatty acid, were also observed. Electrospray tandem mass spectrometry of these ions was performed to confirm the proposed structure of these adducts. All MS/MS spectra showed an ion at m/z 114, correspondent to the [DMPO + H]+, and a fragment ion due to loss of DMPO (loss of 113 Da), confirming that they are DMPO adducts. ES-MS/MS spectra of alkoxyl radical adducts (DMPO/LO*) showed an additional ion at m/z 130 [DMPO - O + H]+, while ES MS/MS of peroxyl radical adducts (DMPO/LOO*) showed a fragment ion at m/z 146 [DMPO - OO + H]+, confirming both structures. Other fragment ions were observed, such as alkyl acylium radical ions, formed by cleavage of the alkyl chain after loss of water and the DMPO molecule. The identification of fragment ions observed in the MS/MS spectra of the different DMPO adducts suggests the occurrence of structural isomers containing the DMPO moiety both at C9 and C13. The use of ES tandem mass spectrometry, associated with spin trapping experiments, has been shown to be a valuable tool for the structural characterization of carbon and oxygen-centered spin adducts of lipid radicals.     

Structural analysis of platycosides in Platycodi Radix by liquid chromatography/electrospray ionization-tandem mass spectrometry

Platycosides extracted from Platycodi Radix were analyzed by HPLC coupled with electrospray ionization multistage tandem mass spectrometry (HPLC/ESI-MS(n)). Predominant [M+Na](+) ions in positive mode and [M-H](-) ions in negative mode in the direct ESI-MS spectra of extract provided information on molecular weights, but minor components and isomers could not be discriminated. However, combining HPLC and ESI-MS(n), allowed eleven platycosides, including four acetylated platycodin isomers and two prosapogenines to be analyzed. During MS(2) analysis conducted to elucidate the structures of platycosides, fragment ions provided information on sugar moieties attached at C-28 of triterpene structure of the platycosides. Glycosidic bond cleavages at C-3 were revealed by fragment ions in MS(3) spectra. Some characteristic fragment ions not related to sugar bond cleavage revealed that an esterified triterpene is linked to sugars at C-28. The only sugar ring-cross cleavage corresponding to 90 Da in the negative MS(2) spectrum took place at an arabinosyl sugar moiety. By using HPLC/ESI-MS(n), three acetylated platycosides in Platycodi Radix extract were newly identified.     

Study of the fragmentation pattern of ketamine‐heptafluorobutyramide by gas chromatography/electron ionization mass spectrometry

Ketamine is an anaesthetic compound used in human and veterinary medicine with hallucinogen properties that have resulted in its increased illicit use by teenagers at rave parties. Although several gas chromatography/mass spectrometry (GC/MS) methods have been reported for the quantification of the drug both in urine and in hair, its electron ionization (EI) fragmentation after derivatization with different reagents has been not yet fully investigated. The present work reports the study of the fragmentation of ketamine, derivatized with heptafluorobutyric anhydride (HFBA‐Ket), using gas chromatography/electron ionization mass spectrometry (GC/EI‐MS). The complete characterization of the fragmentation pattern represented an intriguing exercise and required tandem mass spectrometry (MSⁿ) experiments, high‐resolution accurate mass measurements and the use of deuterated d⁴‐ketamine to corroborate the proposed structures and to characterize the fragment ions carrying the unchanged aromatic moiety. Extensive fragmentation was observed, mainly located at the cyclohexanone ring followed by rearrangement of the fragment ions, as confirmed by the mass spectra obtained from the deuterated molecule. The GC/EI‐MS analysis of HFBA‐Ket will represent a useful tool in forensic science since high‐throughput analyses are enabled, preserving both the GC stationary phase and the cleanliness of the mass spectrometer ion optics. Copyright © 2009 John Wiley & Sons, Ltd.     

Mass spectral studies on aryl-substituted N-carbamoyl/N-thiocarbamoyl narcotine and related compounds

Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage beta to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M + H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M + H]+ ion peaks in good agreement with FAB and ESI studies.     

Structural assignment of isomeric 2-aminopyridine-derivatized oligosaccharides using MSn spectral matching

Two isomeric pairs of 2-aminopyridine (PA)-derivatized fucosylated and non-fucosylated oligosaccharides (complex-type N-glycans of IgG) were analyzed using liquid chromatography/ion trap mass spectrometry (LC/ITMS) with a sonic spray ionization source and by varying the collision-induced dissociation voltage. Reproducibility of MS(n) (n = 2) spectra obtained by LC/ITMS was tested considering both fragment ions (m/z) and intensities. A comparison of their MS(n) spectra and evaluation of similarities (or matching), based on correlation coefficients between MS(n) spectra, was investigated as a possibility for structural assignment of the isomers. It is shown that such MS(n) spectral matching is useful and applicable to the structural assignment of relatively large fucosylated and sialylated PA-oligosaccharides released from IgG based on Bn- and Yn-type fragmentations of the corresponding [M+H+Na](2+) ions.     

Determination of the metabolites of gestrinone in human urine by high performance liquid chromatography, liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry

Gestrinone was studied by high performance liquid chromatography (HPLC) for screening and by gas chromatography/mass spectrometry (GC/MS) for confirmation. When the chromatograms of blank, spiked urine and dosed urine were compared by HPLC, two unknown metabolites were found and these were excreted as the conjugated forms. Metabolites 1 and 2 were tested by LC/MS and LC/MS/MS and both had parent ions at m/z 325. The fragment ion of metabolite 1 was at m/z 263 and ions for metabolite 2 were m/z 307 [MH - H(2)O](+), 289, 279 and 241. LC/MS/MS of m/z 263 as the parent ion of metabolite 1 gave fragment ions at m/z 245 and 217, which were assumed to be [263 - H(2)O](+) and [235 - H(2)O](+), respectively. The trimethylsilyl (TMS)-enol-TMS ether derivative of gestrinone displayed three peaks in its GC/MS chromatogram, formed by tautomerism.     

Distinguishing of 2‐MAPB and 6‐MAPB: Solution of the problem

Differentiation of new psychoactive substance (NPS), 6‐(2‐methylaminopropyl)benzofuran (6‐MAPB), and its positional isomer, 2‐(2‐methylaminopropyl)benzofuran (2‐MAPB), by means of gas chromatography/mass spectrometry (GC/MS) with quadrupole detection is ambiguous. Reliable distinguishing of the two isomers could be achieved by MS/MS spectra recorded after collision‐induced dissociation (CID) of precursor ions. Both electron ionization (EI) and electrospray ionization (ESI) methods could be used for these purposes.     

Structure Analysis and Ion Abundance in CID- MS- MS Spectra of Isomeric Oligosaccharides Using Quadrupole Time-of- flight Mass Spectrometry: Distinguishing between Isomeric Oligosaccharides

N - Linked oligosaccharide were analyzed by using electrospray ionization (ESI) quadrupole time - of- fight mass spectrometry(Q - Tof MS).The isomers showed the same MS and collisioninduced desociation(CID) MS - MS spectra in the m/z values because the sequence of the sugar residues was the same.But the relative ion abundance of the specific fragment ion was greatly different between the isomers.So, the isomeric oligosacchariedes were distinguished by using the ion abundance in their CID -MS - MS spectra.Discussing the ion abundance in accurate level, quantitative analysis of the mixtures of isomers were also performed.     

Analysis of hydroxy fatty acids as pentafluorobenzyl ester,trimethylsilyl ether derivatives by electron ionization gas chromatography/mass spectrometry

Electron ionization (EI) gas chromatography/mass spectrometry (GC/MS) analysis of pentafluorobenzyl ester-trimethyl sllyl ether (PFB-TMS) derivatives of hydroxy-subshtuted fatty acids provides structural information comparable to that obtained in analysis of methyl ester-trimethyl silyl ether (Me-TMS) derivatives. Use of this derivative eliminates the need to prepare two separate derivatives, the PFB-TMS derivative for molecular weight determination by electron capture ionization (negative ions) analysis and the Me-TMS derivative for structural determination by EI GC/MS analysis. The relative abundance of fragment ions observed during EI GC/MS analysis of these derivatized unsaturated fatty acids indicates the location of the —OTMS substituents relative to double bond positions in those cases studied. The most abundant fragment ions are observed when the compound contains an unsaturation two carbon atoms removed from the —OTMS ether carbon (the β-OTMS position). The “saddle effect” observed in the GC/MS analyses of some derivatized monohy— droxy unsaturated fatty acids is suggested to be due to a thermally allowed pericyclic double bond rearrangement and indicates the presence of a conjugated diene one carbon atom removed from the —OTMS ether carbon (the α-OTMS position). The saddle effect is most prominent for fatty acids that contain additional unsaturation separated by a single methylene unit from the conjugated diene moiety.     

Differentiation of diastereomeric N-aryltetrahydropyrano/tetrahydrofuranochromenylamines under electron ionization and chemical ionization conditions

A series of diastereomeric 4S,5S,6R/S-tetrahydropyrano- and 3S,4S,5R/S-tetrahydrofuranochromenylamine derivatives (a/b isomers; 1-26) has been studied under electron ionization (EI) and chemical ionization (CI) conditions. The EI mass spectra of all diastereomeric compounds show two characteristic fragment ions, of which one is formed by retro-Diels-Alder (RDA) reaction from the molecular ion, retaining the charge on the diene fragment, and the other [M-(HNAr)]+ ion by a simple radical loss. The RDA process is more favorable in all b isomers, whereas the radical loss is dominant in all a isomers; based on these two ions it is easy to differentiate the two diastereomers. The collision-induced dissociation (CID) spectra of all the molecular ions also show the same trend, which reflects the stereoselectivity in the formation of the two characteristic fragment ions. The results of theoretical calculations performed are in accordance with the experimental observations. The CI experiments (methane and isobutane) on all the diastereomeric compounds also enabled the differentiation of the isomers.     

Mass spectra of 1,2-alkylenedioxy-substituted and related benzofurazans and benzofuroxans: differentiation between linear and angular isomers.

The electron ionization (EI) mass spectra of [1,3]-dioxolo-, 6, 7-dihydro-[1,4]-dioxino-, 7,8-dihydro-6H-[1,4]dioxepino-, 6,7,8, 9-tetrahydro[1,4]dioxocino-, 7,8,9,10-tetrahydro-6H-[1,4]dioxonino- and 6,7,8,9,10,11-hexahydro[1,4]dioxecino[2,3-f]-2,1, 3-benzoxadiazoles (benzofurazans) and the corresponding 1-oxides (benzofuroxans), all linear isomers, are reported. Also reported are the EI mass spectra of the corresponding angular isomers, [1, 3]dioxolo-, 7,8-dihydro[1,4]dioxino-, 8,9-dihydro-7H-[1,4]dioxepino-, 7,8,9,10-tetrahydro[1,4]dioxocino-, 8,9,10,11-tetrahydro-7H-[1, 4]dioxonino-, 7,8,9,10,11,12-hexahydro[1,4]dioxecino[2,3-e]-2,1, 3-benzoxadiazoles and the corresponding 1-oxides. The relative abundance of the fragment ion of m/z 80 is characteristically enhanced in the spectra of the angular derivatives compared to the spectra of the linear counterparts. Collisionally activated decomposition studies show that it is structurally identical whether derived from the benzofurazans or the benzofuroxans. The relative abundance of the m/z 80 ion serves to distinguish between linear and angular isomeric pairs. In addition, the fragment ion at m/z 80 also serves to differentiate between the pairs of isomers, analogous to linear and angular, of six acyclic methoxy- and methoxymethyl-substituted benzofurazans and their corresponding benzofuroxans.     

Investigation of the electrochemical oxidation products of zotepine and their fragmentation using on-line electrochemistry/electrospray ionization mass spectrometry

When zotepine, an antipsychotic drug, was electrochemically oxidized using electrospray ionization mass spectrometry (ESI-MS) coupled with a microflow electrolytic cell, [M + 16 + H]+ (m/z 348), [M-H]+ (m/z 330) and [M-14 + H]+ (m/z 318) were observed as electrochemical oxidation product ions (M represents the zotepine molecule). Although a major fragment ion that was derived from the dimethyl aminoethyl moiety was observed only at m/z 72 in the collision-induced dissociation (CID) spectrum of zotepine, new fragments such as m/z 315 and 286 ions could be generated in the CID spectrum by combining electrochemical oxidation and CID. Since these fragments were relatively specific with high ion strength, it was thought that they would be useful for developing a sensitive LC-MS/MS assay. The S-oxide and N-demethylated products were detected by electrolysis assuring that a portion of P450 metabolites of zotepine could be mimicked by the electrochemistry/electrospray ionization mass spectrometry (EC/ESI-MS) system.     

Mass spectra of 3,3-difluoro-1-halo-2-arylcyclopropenes

The electron ionization (EI) mass spectra of a series of 3,3-difluoro-1-halo-2-arylcyclo- propenes (1, 2) give the fragments [M-X](+) (X: Br, Cl) as the base peaks. A comparison of tandem mass spectrometry (MS/MS) profiles of the m/z 151 ions recorded from compounds 1 and 2 and 3-bromo-3,3-difluoro-1-phenylcyclopropyne (5), 1,1,2,2-tetrafluoro-3-phenyl- cyclopropane (6), 1,1,2,2-tetrafluoroindane (7), and 2,3,3-trifluoroindene (8) suggested that the structure of the derived [M-X](+) fragment ion is more likely that of a substituted cyclopropenium ion. The results from calculations using the density functional theory (DFT) method support this MS/MS analysis.     

Deuterium exchange studies in the identification of alkylated DNA bases found in urine, by tandem mass spectrometry

Humans are exposed to a large number of carcinogens which may react at various sites throughout the body, including the N-7-, N2-, and O6-positions of guanine. The effects of this are various but may result in depurination and eventual excretion of the modified base in the urine. Various alkylguanine derivatives with substituents at the N-7-, N2- and O6-positions were synthesized and daughter-ion spectra obtained. Apart from the methyl and dialkylguanines all other spectra exhibited an ion at m/z 151 using electron ionization (EI) and m/z 152 using fast-atom bombardment (FAB). The daughter-ion spectra of dialkylguanines contained an ion at m/z 150 (EI). Hence, scans of m/z 150 and 151 using EI, to detect all parent-ions from which they are formed (parent-ion scans) should indicate the presence of alkyl and dialkylguanine bases in a complex biological matrix such as human urine. Parent-ion scans of m/z 150 and 151 (EI) of a partially purified human urine sample exhibited numerous ions, including a prominent ion at m/z 179. A daughter-ion spectrum of m/z 179 revealed fragment ions that suggested the presence of N2-dimethylguanine and an ethylated guanine. Any confusion due to the presence of daughter ions from different alkylguanines in the same spectrum can be resolved by the fact that an ethylated guanine has four exchangeable protons, whereas N2-dimethylguanine has only three. By performing hydrogen/deuterium exchange it is possible to distinguish the N2-dimethylguanine from ethylated guanine isomers.(ABSTRACT TRUNCATED AT 250 WORDS)     

GC-MS and GC-IRD studies on the ring isomers of N-methyl-2-methoxyphenyl-3-butanamines (MPBA) related to 3,4-MDMA

The mass spectra of the controlled substance 3,4-MDMA and its regioisomer 2,3-MDMA are characterized by an imine fragment base peak at m/z 58 and additional fragments at m/z 135/136 for the methylenedioxybenzyl cation and radical cation, respectively. Three positional ring methoxy isomers of N-methyl-2-(methoxyphenyl)-3-butanamine (MPBA) have an isobaric relationship to 2,3- and 3,4-MDMA. All five compounds have the same molecular weight and produce similar EI mass spectra. This lack of mass spectral specificity for the isomers in addition to the possibility of chromatographic co-elution could result in misidentification. The lack of reference materials for the potential imposter molecules constitutes a significant analytical challenge. Perfluoroacylation of the amine group reduced the nitrogen basicity and provided individual fragmentation pathways for discrimination among these compounds based on unique fragment ions and the relative abundance of common ions. Studies using gas chromatography with infrared detection provided additional structure-IR spectra relationships. The underivatized amines and the perfluoroacylated derivatives (PFPA and HFBA) were resolved by capillary gas chromatography on a 100% dimethylpolysiloxane stationary phase. The perfluoroacylated derivatives showed better resolution on a cyclodextrin modified stationary phase.     

Gas chromatography/mass spectrometry determination of amphetamine-related drugs and ephedrines in plasma, urine and hair samples after derivatization with 2,2,2-trichloroethyl chloroformate

A new analytical approach, based on derivatization with 2,2,2-trichloroethyl chloroformate and gas chromatography/mass spectrometry (GC/MS), was investigated for qualitative and quantitative analyses of a large range of amphetamine-related drugs and ephedrines in plasma, urine and hair samples. Sample preparation involved alkaline extraction of analytes from biological samples using Extrelut columns, after addition of the internal standard 3,4-methylenedioxypropylamphetamine (MDPA), and subsequent derivatization to produce 2,2,2-trichloroethylcarbamates. GC/MS analyses, in splitless mode using a slightly polar 30-m capillary column, were performed with quadrupole or ion trap instruments. MS acquisition modes were electron ionization (EI) in full-scan or selected ion monitoring (SIM) modes (quadrupole), and full-scan MS or MS/MS modes with chemical ionization (CI) conditions (ion trap). EI spectra of 2,2,2-trichloroethylcarbamates showed variably abundant molecular ions as well as abundant diagnostic fragment ions, both characterized by ion clusters reflecting the isotope distribution of three chlorine atoms in the derivatized molecules. CI spectra showed abundant protonated molecules. Quantitative studies using EI SIM conditions gave recoveries in the range 74-89%, linear response over ranges of 10-2000 ng/mL (plasma and urine) and 0.20-20 ng/mg (hair), with corresponding limits of detection in the ranges 2-5 ng/mL and 0.1-0.2 ng/mg. Potential applications (following full method validation) include clinical and forensic toxicology, as well as doping control.