A differentially pumped dual linear quadrupole ion trap (DLQIT) mass spectrometer: a mass spectrometer capable of MS(n) experiments free from interfering reactions.

A novel differentially pumped dual linear quadrupole ion trap (DLQIT) mass spectrometer was designed and built to facilitate tandem MS experiments free from interfering reactions. The instrument consists of two differentially pumped Thermo Scientific linear quadrupole ion trap (LQIT) systems that have been connected via an ion transfer octupole encased in a machined manifold. Tandem MS experiments can be performed in the front trap and then the resulting product ions can be transferred via axial ejection into the back trap for further, independent tandem MS experiments in a differentially pumped area. This approach allows the examination of consecutive collision-activated dissociation (CAD) and ion-molecule reactions without unwanted side reactions that often occur when CAD and ion-molecule reactions are examined in the same space. Hence, it greatly facilitates investigations of ion structures. In addition, the overall lower pressure of the DLQIT, as compared to commercial LQIT instruments, results in a reduction of unwanted side reactions with atmospheric contaminants, such as water and oxygen, in CAD and ion-molecule experiments.

High-performance liquid chromatography/high-resolution multiple stage tandem mass spectrometry using negative-ion-mode hydroxide-doped electrospray ionization for the characterization of lignin degradation products.

In the search for a replacement for fossil fuel and the valuable chemicals currently obtained from crude oil, lignocellulosic biomass has become a promising candidate as an alternative biorenewable source for crude oil. Hence, many research efforts focus on the extraction, degradation, and catalytic transformation of lignin, hemicellulose, and cellulose. Unfortunately, these processes result in the production of very complex mixtures. Further, while methods have been developed for the analysis of mixtures of oligosaccharides, this is not true for the complex mixtures generated upon degradation of lignin. For example, high-performance liquid chromatography/multiple stage tandem mass spectrometry (HPLC/MS(n)), a tool proven to be invaluable in the analysis of complex mixtures derived from many other biopolymers, such as proteins and DNA, has not been implemented for lignin degradation products. In this study, we have developed an HPLC separation method for lignin degradation products that is amenable to negative-ion-mode electrospray ionization (ESI doped with NaOH), the best method identified thus far for ionization of lignin-related model compounds without fragmentation. The separated and ionized compounds are then analyzed by MS(3) experiments to obtain detailed structural information while simultaneously performing high-resolution measurements to determine their elemental compositions in the two parts of a commercial linear quadrupole ion trap/Fourier-transform ion cyclotron resonance mass spectrometer. A lignin degradation product mixture was analyzed using this method, and molecular structures were proposed for some components. This methodology significantly improves the ability to analyze complex product mixtures that result from degraded lignin.

Carbon disulfide reagent allows the characterization of nonpolar analytes by atmospheric pressure chemical ionization mass spectrometry.

While atmospheric pressure ionization methodologies have revolutionized the mass spectrometric analysis of nonvolatile analytes, limitations native to the chemistry of these methodologies hinder or entirely inhibit the analysis of certain analytes, specifically, many nonpolar compounds. Examination of various analytes, including asphaltene and lignin model compounds as well as saturated hydrocarbons, demonstrates that atmospheric pressure chemical ionization (APCI) using CS(2) as the reagent produces an abundant and stable molecular ion (M(+•)) for all model compounds studied, with the exception of completely saturated aliphatic hydrocarbons and the two amino acids tested, arginine and phenylalanine. This reagent substantially broadens the applicability of mass spectrometry to nonvolatile nonpolar analytes and also facilitates the examination of radical cation chemistry by mass spectrometry.

Dental resins used in 3D printing technologies release ovo-toxic leachates.

We recently engineered the first female reproductive tract on a chip (EVATAR), to enable sex-based ex vivo research. To increase the scalability and accessibility of EVATAR, we turned to 3D printing (3DP) technologies, selecting two biocompatible 3DP resins, Dental SG (DSG) and Dental LT (DLT) to generate 3DP microphysiologic platforms. Due to the known sensitivity of reproductive cells to leachable compounds, we first screened for toxicity of these biomaterials using an in vitro mammalian oocyte maturation assay. Culture of mouse oocytes in 3DP plates using conventionally treated DSG resin resulted in rapid oocyte degeneration. Oxygen plasma treatment of the surface of printed DSG resin prevented this degeneration, and the majority of the resulting oocytes progressed through meiosis in vitro. However, 57.0% ± 37.2% of the cells cultured in the DSG resin plates exhibited abnormal chromosome morphology compared to 19.4% ± 17.3% of controls cultured in polystyrene. All tested DLT resin conditions, including plasma treatment, resulted in complete and rapid oocyte degeneration. To identify the ovo-toxic component of DLT, we analyzed DLT leachate using mass spectroscopy. We identified Tinuvin 292, a commercial light stabilizer, as a major component of the DLT leachate, which resulted in a dose-dependent disruption of meiotic progression and increase in chromosomal abnormalities with oocyte exposure, showing significant ovo-toxicity in mammals. Severe reproductive toxicity induced by in vitro exposure to these 3D-printed resins highlights potential risks of deploying insufficiently characterized materials for biomedical applications and underscores the need for more rigorous evaluation and designation of biocompatible materials.

Laser-Induced Acoustic Desorption/Electron Ionization of Amino Acids and Small Peptides.

Laser-induced acoustic desorption (LIAD) allows for desorption of neutral nonvolatile compounds independent of their volatility or thermal stability. Many different ionization methods have been coupled with LIAD. Hence, this setup provides a better control over the types of ions formed than other mass spectrometry evaporation/ionization methods commonly used to characterize biomolecules, such as ESI or MALDI. In this study, the utility of LIAD coupled with electron ionization (EI) was tested for the analysis of common amino acids with no derivatization. The results compared favorably with previously reported EI mass spectra obtained using thermal desorption/EI. Further, LIAD/EI mass spectra collected for hydrochloride salts of two amino acids were found to be similar to those measured for the neutral amino acids with the exception of the appearance of an HCl+● ion. However, the hydrochloride salt of arginine showed a distinctly different LIAD/EI mass spectrum than the previously published literature EI mass spectrum, likely due to its highly basic side chain that makes a specific zwitterionic form particularly favorable. Finally, EI mass spectra were measured for seven small peptides, including di-, tri-, and tetrapeptides. These mass spectra show a variety of ion types. However, an type ions are prevalent. Also, electron-induced dissociation (EID) of protonated peptides has been reported to form primarily an type ions. In addition, the loss of small neutral molecules and side-chain cleavages were observed that are reminiscent of other high-energy fragmentation methods, such as EID. Finally, the isomeric dipeptides LG and IG were found to produce drastically different EI mass spectra, thus allowing differentiation of the leucine and isoleucine amino acids in these dipeptides. Graphical Abstract ᅟ.

A Fundamental Tandem Mass Spectrometry Study of the Collision-Activated Dissociation of Small Deprotonated Molecules Related to Lignin.

The collision-activated fragmentation pathways and reaction mechanisms of 34 deprotonated model compounds representative of lignin degradation products were explored experimentally and computationally. The compounds were evaporated and ionized by using negative-ion mode electrospray ionization doped with NaOH to produce abundant deprotonated molecules. The ions were isolated and subjected to collision-activated dissociation (CAD). Their fragment ions were then isolated and also subjected to CAD. This was repeated until no further fragmentation was observed (up to MS6 ). This approach enabled the identification of characteristic reaction pathways and delineation of reasonable fragmentation mechanisms for deprotonated molecules containing various functional groups. The varying fragmentation patterns observed for different types of compounds allow for the identification of the functionalities in these compounds. This information was utilized to identify the presence of specific functionalities and their combinations in molecules in an organosolv lignin sample.

HPLC/APCI mass spectrometry of saturated and unsaturated hydrocarbons by using hydrocarbon solvents as the APCI reagent and HPLC mobile phase.

Saturated and unsaturated, linear, branched, and cyclic hydrocarbons, as well as polyaromatic and heteroaromatic hydrocarbons, were successfully ionized by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as reagents in a linear quadrupole ion trap (LQIT) mass spectrometer. Pentane was proved to be the best reagent among the hydrocarbon reagents studied. This ionization method generated different types of abundant ions (i.e., [M + H](+), M(+•), [M - H](+) and [M - 2H](+ •)), with little or no fragmentation. The radical cations can be differentiated from the even-electron ions by using dimethyl disulfide, thus facilitating molecular weight (MW) determination. While some steroids and lignin monomer model compounds, such as androsterone and 4-hydroxy-3-methoxybenzaldehyde, also formed abundant M(+•) and [M + H](+) ions, this was not true for all of them. Analysis of two known mixtures as well as a base oil sample demonstrated that each component of the known mixtures could be observed and that a correct MW distribution was obtained for the base oil. The feasibility of using this ionization method on the chromatographic time scale was demonstrated by using high-performance liquid chromatography (HPLC) with hexane as the mobile phase (and APCI reagent) to separate an artificial mixture prior to mass spectrometric analysis.

Laser-induced acoustic desorption/atmospheric pressure chemical ionization mass spectrometry.

Laser-induced acoustic desorption (LIAD) was successfully coupled to a conventional atmospheric pressure chemical ionization (APCI) source in a commercial linear quadrupole ion trap mass spectrometer (LQIT). Model compounds representing a wide variety of different types, including basic nitrogen and oxygen compounds, aromatic and aliphatic compounds, as well as unsaturated and saturated hydrocarbons, were tested separately and as a mixture. These model compounds were successfully evaporated into the gas phase by using LIAD and then ionized by using APCI with different reagents. From the four APCI reagent systems tested, neat carbon disulfide provided the best results. The mixture of methanol and water produced primarily protonated molecules, as expected. However, only the most basic compounds yielded ions under these conditions. In sharp contrast, using APCI with either neat benzene or neat carbon disulfide as the reagent resulted in the ionization of all the analytes studied to predominantly yield stable molecular ions. Benzene yielded a larger fraction of protonated molecules than carbon disulfide, which is a disadvantage. A similar but minor amount of fragmentation was observed for these two reagents. When the experiment was performed without a liquid reagent (nitrogen gas was the reagent), more fragmentation was observed. Analysis of a known mixture as well as a petroleum cut was also carried out. In summary, the new experiment presented here allows the evaporation of thermally labile compounds, both polar and nonpolar, without dissociation or aggregation, and their ionization to predominantly form stable molecular ions.

Differentiation of regioisomeric aromatic ketocarboxylic acids by positive mode atmospheric pressure chemical ionization collision-activated dissociation tandem mass spectrometry in a linear quadrupole ion trap mass spectrometer.

Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS(n)) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer. Energy-resolved collision-activated dissociation (CAD) experiments carried out on the protonated analytes revealed fragmentation patterns that varied based on the location of the functional groups. Unambiguous differentiation between the regioisomers was achieved in each case by observing different fragmentation patterns, different relative abundances of ion-molecule reaction products, or different relative abundances of fragment ions formed at different collision energies. The mechanisms of some of the reactions were examined by H/D exchange reactions and molecular orbital calculations.