Differentiation of protonated aromatic regioisomers related to lignin by reactions with trimethylborate in a Fourier transform ion cyclotron resonance mass spectrometer

A Modified Traveling Wave Ion Mobility Mass Spectrometer as a Versatile Platform for Gas-Phase Ion-Molecule Reactions

Taken individually, chemical labeling and mass spectrometry are two well-established tools for the structural characterization of biomolecular complexes. A way to combine their respective advantages is to perform gas-phase ion-molecule reactions (IMRs) inside the mass spectrometer. This is, however, not so well developed because of the limited range of usable chemicals and the lack of commercially available IMR devices. Here, we modified a traveling wave ion mobility mass spectrometer to enable IMRs in the trapping region of the instrument. Only one minor hardware modification is needed to allow vapors of a variety of liquid reagents to be leaked into the trap traveling wave ion guide of the instrument. A diverse set of IMRs can then readily be performed without any loss in instrument performance. We demonstrate the advantages of implementing IMR capabilities in general, and to this quadrupole-ion mobility-time-of-flight (Q-IM-TOF) mass spectrometer in particular, by exploiting the full functionality of the instrument, including mass selection, ion mobility separation, and post-mobility fragmentation. The potential to carry out gas-phase IMR kinetics experiments is also illustrated. We demonstrate the versatility of the setup using gas-phase IMRs of established utility for biological mass spectrometry, including hydrogen-deuterium exchange, ion-molecule proton transfer reactions, and covalent modification of DNA anions using trimethylsilyl chloride.

Conversion of benzoic acid into phenol in an ITMS under CI-MSn conditions. Recognition of ortho-chlorobenzoyl derivatives

Isomeric chlorobenzoyl cations (m/z 139), under collision-induced experiments, fragment identically. Chlorobenzoyl cations can be efficiently converted into cholorophenol radical cations by the reaction with methanol in the ion trap analyzer under CI-MSn conditions. The substitution of the carbonyl group with a hydroxyl moiety is able to induce an ortho effect, which is absent in the startingortho-chlorobenzoyl cation. This transformation could be useful to recognize ortho-chlorinated benzoyl derivatives without the need of MS spectrum comparison of the whole set of isomers. The method reported in this study could be applicable to biologically active molecules that dissociate to form the chlorobenzoyl cations under CI or CI collision-induced dissociation conditions, such as indomethacin, the degradation products from the insect growth regulator 1-(2-chlorobenzoyl)-3-(4-chlorophenyl) urea, and lorazepam.

Gas-phase ion-molecule reactions for the identification of the sulfone functionality in protonated analytes in a linear quadrupole ion trap mass spectrometer

RATIONALE

The oxidation of sulfur atoms is an important biotransformation pathway for many sulfur-containing drugs. In order to rapidly identify the sulfone functionality in drug metabolites, a tandem mass spectrometric method based on ion-molecule reactions was developed.

METHODS

A phosphorus-containing reagent, trimethyl phosphite (TMP), was allowed to react with protonated analytes with various functionalities in a linear quadrupole ion trap mass spectrometer. The reaction products and reaction efficiencies were measured.

RESULTS

Only protonated sulfone model compounds were found to react with TMP to form a characteristic [TMP adduct-MeOH] product ion. All other protonated compounds investigated, with functionalities such as sulfoxide, N-oxide, hydroxylamino, keto, carboxylic acid, and aliphatic and aromatic amino, only react with TMP via proton transfer and/or addition. The specificity of the reaction was further demonstrated by using a sulfoxide-containing anti-inflammatory drug, sulindac, as well as its metabolite sulindac sulfone.

CONCLUSIONS

A method based on functional group-selective ion-molecule reactions in a linear quadrupole ion trap mass spectrometer has been demonstrated for the identification of the sulfone functionality in protonated analytes. A characteristic [TMP adduct-MeOH] product ion was only formed for the protonated sulfone analytes. The applicability of the TMP reagent in identifying sulfone functionalities in drug metabolites was also demonstrated. Copyright © 2016 John Wiley & Sons, Ltd.

Identification of the sulfoxide functionality in protonated analytes via ion/molecule reactions in linear quadrupole ion trap mass spectrometry

A mass spectrometric method utilizing gas-phase ion/molecule reactions of 2-methoxypropene (MOP) has been developed for the identification of the sulfoxide functionality in protonated analytes in a LQIT mass spectrometer. Protonated sulfoxide analytes react with MOP to yield an abundant addition product (corresponding to 37-99% of the product ions), which is accompanied by a much slower proton transfer. The total efficiency (percent of gas-phase collisions leading to products) of the reaction is moderate (3-14%). A variety of compounds with different functional groups, including sulfone, hydroxylamino, N-oxide, aniline, phenol, keto, ester, amino and hydroxy, were examined to probe the selectivity of this reaction. Most of the protonated compounds with proton affinities lower than that of MOP react mainly via proton transfer to MOP. The formation of adduct-MeOH ions was found to be characteristic for secondary N-hydroxylamines. N-Oxides formed abundant MOP adducts just like sulfoxides, but sulfoxides can be differentiated from N-oxides based on their high reaction efficiencies. The reaction was tested by using the anti-inflammatory drug sulindac (a sulfoxide) and its metabolite sulindac sulfone. The presence of a sulfoxide functionality in the drug but a sulfone functionality in the metabolite was readily demonstrated. The presence of other functionalities in addition to sulfoxide in the analytes was found not to influence the diagnostic reactivity.

Mass spectrometric identification of the N-monosubstituted N-hydroxylamino functionality in protonated analytes via ion/molecule reactions in tandem mass spectrometry

RATIONALE

N-Monosubstituted hydroxylamines correspond to an important class of metabolites for many bioactive molecules. In this study, a tandem mass spectrometric method based on ion/molecule reactions was developed for the identification of compounds with the N-monosubstituted hydroxylamino functionality.

METHODS

The diagnostic ion/molecule reaction occurs between protonated analytes with 2-methoxypropene (MOP) inside a linear quadrupole ion trap mass spectrometer.

RESULTS

Most protonated compounds with N-monosubstituted and disubstituted hydroxylamino and oxime functional groups react with MOP via proton transfer and formation of a stable adduct in a linear quadrupole ion trap mass spectrometer. However, only protonated compounds with N-monosubstituted hydroxylamino groups form the characteristic MOP adduct-MeOH product. Possible mechanisms of this reaction are discussed.

CONCLUSIONS

A method based on functional group-selective ion/molecule reactions in a linear quadrupole ion trap mass spectrometer has been demonstrated to allow the identification of protonated compounds with the N-monosubstituted hydroxylamino functionality. Only N-monosubstituted hydroxylamines react with MOP via formation of an adduct that has eliminated methanol.

Evaluation of the α-phenylvinyl cation as a chemical ionization reagent for the differentiation of isomeric substituted phenols in an ITMS

Ion-molecule reactions between the α-phenylvinyl cation and isomeric naturally occurring phenols were investigated using a quadruple ion trap mass spectrometer. The α-phenylvinyl cation m/z 103, generated by chemical ionization from phenylacetylene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103](+) adduct ions and the trans-vinylating product ions [M + 25](+) , which correspond to [M + 103](+) adduct after the loss of benzene. Isomeric differentiation of several ring-substituted phenols was achieved by using collision-induced dissociation of the [M + 103](+) adduct ions. This method also showed to be effective in the differentiation of 4-ethylguaiacol from one of its structural isomers that displays identical EI and EI/MS/MS spectra. The effects of gas-phase alkylation with phenylvinyl cation on the dissociation behavior were examined using mass spectrometry(n) and labeled derivatives. Copyright © 2015 John Wiley & Sons, Ltd.

A novel UV-MALDI-MS analytical approach for determination of halogenated phenyl-containing pesticides

The paper highlighted the capability of the UV-MALDI mass spectrometry, employing the Orbitrap analyzer for solid-state assay of halogenated phenyl-pesticides in mixtures. It is successfully applied for the analysis of eighteen (1)-(18) molecular objects of Fenarimol (1) type and their condensation products (P5)-(P12). The full method and technique validation is performed using the dried droplet sample preparation technique on embedded analytes in novel organic matrix crystals of N-(1H-benzoimidazol-2-yl)-guanidine (M4) and (E)-phenyl-2-pyridyl ketone oxime (M5), resulting to successful ionization of the analytes. Since the sampling technique in the UV-MALDI method is a key step in the overall process impacting significantly the metrology through the reproducibility of the data, the crystallization of M4, M5 and matrix-analyte in situ morphology of the samples is controlled by single crystal X-ray diffraction. The achieved promising metrology of LODs, of 0.46ngkg(-1) (1.53ngkg(-1) LOQs), is several orders of magnitude lower than the reported ecotoxicological effect values of studied pesticides. It is confirmed by the partial validated protocol based on ESI-MS. Inasmuch that LC-MS/MS is a method of choice for foodstuffs monitoring of organic contaminations, due to its routine quantitative analytical procedures, it is often characterized with the difficulties of the chromatographic separation of the closely structured analytes at a large scale of experimental conditions, complex multi-step sampling pretreatments, which inevitably alert the variables through the systematic and random errors. In this respect, notwithstanding the complex quantitative UV-MALDI-Orbitrap-MS procedure, conceptually different from the LC-MS/MS one, its high resolving power, capability for achieving meaningful analytical qualitative, quantitative and structural information of low-molecular weight analytes, its instrumental and sampling operation flexibility, applicable for a large scale of foodstuff matrices, and operating at the analyte concentrations of up to fgg(-1) make UV-MALDI-Orbitrap-MS a perspective method of choice for an extensive implementation in the foodstuffs monitoring practice for control of the most essential task related to the assessment of the human health risks from environmental and foodstuff contaminations.