Real Time Ion Source Research Articles

Direct Identification of Disaccharide Structural Isomers Using Ambient Ionization Tandem Mass Spectrometry with In Situ Methylation.

Carbohydrates play critically important roles in energy supply and biological functions in living systems. However, it has been a great challenge to identify saccharides and distinguish their isomers because they have highly similar structures and many possible positions for glycosidic linkages. In this work, an ambient ionization tandem mass spectrometry method was developed to characterize disaccharide structural isomers with in situ methylation. The direct analysis in real time ion source can be used to facilitate the methylation reaction of disaccharides with tetramethylammonium hydroxide. The hydroxyl groups of disaccharides can be methylated instantaneously, and the products can be ionized at the same time. The methylated product ions from full scan mass spectrometry (MS) and tandem MS can be used to distinguish a variety of disaccharide structural isomers with different glycosidic linkages, compositions, and configurations. Characteristic marker ions were discovered, and they can be used for the assignment of linkage type and identification of specific isomeric forms. The method was used for the direct identification of disaccharide isomers from real commercial products such as honey, wine, and milk without complex sample pretreatment or chromatographic separation.

High-resolution mass spectrometry exhalome profiling with a modified direct analysis in real time ion source.

Exhaled breath contains many substances that are closely related to human metabolism. Analysis of its composition is important for human health, but it is difficult. Since the volatile molecules in breath samples are exhaled instantaneously, easily diffused and modified, and at low level of presence, they are difficult to identify and quantify. A modified direct analysis in real time ion source was used for high-resolution mass spectrometry measurement of human metabolites in exhaled breath through online monitoring and offline analysis, in both positive and negative ion modes. The improved system enabled the breath volatiles as well as condensates to be directly sampled, rapidly transmitted and efficiently ionized in a confined region, and then detected using an Orbitrap mass analyzer. The molecular features with online and offline analysis of exhaled breath were demonstrated with obvious differences. A total ofabout 65 metabolites in positive ion mode and about 55 metabolites in negative ion mode were identified based on accurate m/z values. Exhalome profile and the composition proportion of different classes of compounds were obtained. The relative contents of metabolites from breath varied during different time periods throughout a day. A more complete picture of the human breath metabolome was provided combining the results obtained from both online and offline analysis. The developed method allows analysis of breath samples with different status rapidly and directly, and it features simple operation and metabolite identification, requiring little or no sample preparation.

Critical comparison of direct analysis in real time orbitrap mass spectrometry (DART-Orbitrap MS) towards liquid chromatography mass spectrometry (LC-MS) for mycotoxin detection in cereal matrices

Foodstuffs contaminated by mycotoxins have been reported around the globe resulting in significant financial losses and health-threating cases due to dietary exposure. Commonly, two analytical approaches are used in mycotoxin analysis, namely screening bioanalytical methods such as immunoassays and confirmatory chromatographic analysis which are related to certain merits and challenges. In this study, to provide an alternative combining rapidness and unequivocal analyte identification, a direct analysis in real time ion source coupled to orbitrap mass spectrometry (DART-Orbitrap MS) method was developed and validated for the detection of 19 mycotoxins in cereal flour matrices. Excellent detectability expressed as the lowest calibration level (LCL) ranging between 25 μg kg −1 and 250 μg kg −1 depending on the analyte was achieved as well as satisfactory precision and trueness. To identify advantages and drawbacks of the in-house DART-Orbitrap MS method against the golden standard methods, a critical comparison towards liquid chromatography (LC) coupled to high and low resolution MS was performed. DART-Orbitrap MS high throughput and rapidity was revealed while LC-MS proved its superior detectability, which is of indispensable importance for mycotoxin regulatory control. In conclusion, the developed DART-Orbitrap MS method can be applied to intensify and accelerate the monitoring of specific mycotoxins in cereal matrices. • Rapid detection of 19 mycotoxins in cereal flour matrices using a DART-MS method. • Fit-for-purpose results and excellent analytical performance were achieved. • Critical comparison towards LC-MS revealed DART-MS potential in food control.

Effect of Agroecological Conditions on Biologically Active Compounds and Metabolome in Carrot.

Carrot serves as a source of health-beneficial phytochemicals for human diet whose content is affected by agroecological conditions. The effect of conventional, integrated and organic farming on ascorbic acid (AA) and α,β-carotene levels of new carrot cultivars Cortina F1 and Afalon F1 was investigated and their metabolomic profiles were measured by direct analysis in real time ion source coupled with a high-resolution mass spectrometer (DART-HRMS). Cortina and Afalon exhibited high levels of AA and total carotenes under all agroecological conditions tested that fluctuated in broad ranges of 215–539 and 173–456 mg AA.kg−1 dry biomass and 1069–2165 and 1683–2165 mg carotene.kg−1 dry biomass, respectively. The ratio of β- to α-carotene in both cultivars was about 1.3. The most important variable for the PCA and the partial least squares discriminant analysis (PLS-DA) models for ethyl acetate extracts measured in positive and negative ionization mode was 6-methoxymellein (6-MM). Total carotene content and 6-MM levels were higher in the organic carrot compared to the conventional one and were correlated with a higher level of spontaneous infection. Other important compounds identified were sitosterol, hexose and various organic acids including antioxidant ferulic and coumaric acids. The findings allow comparison of metabolomic profiles and the AA and carotene contents of both cultivars with those of other commercially used carrots.

Structural features of liquefaction residue from Shenmu-Fugu subbituminous coal

Liquefaction residue (LRSFSBC) from Shenmu-Fugu subbituminous coal was ultrasonically extracted with petroleum ether, methanol, cyclohexane, ethyl acetate, acetone, carbon disulfide (CDS) and isometric CDS/acetone mixture (IMCDSAM), respectively. A number of alkanes, arenes, arenols, alkanols, alkenones, esters, and nitrogen-containing organic compounds were identified according to the analyses with Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer, direct analysis in real-time ionization source coupled with ion trap mass spectrometer, and solid-state 13C nuclear magnetic resonance (SS 13C NMR). The tetra- and penta-substituted anthracene or phenanthrene unit could be the average structures in LRSFSBC by SS 13C NMR analysis. The main intermolecular interactions among the organic species in LRSFSBC are π–hydrogen bonds and π–π interactions. These interactions are also the cause for “capsule” formation. Stronger interactions between LRSFSBC and solvents, especially CDS and IMCDSAM, destroyed the interactions and thereby led to high extract yields.

Selective production and characterization of aromatic carboxylic acids from Xianfeng lignite-derived residue by mild oxidation in aqueous H2O2 solution

Lignites show great potential as feedstock for the production of valuable carboxylic acids by mild oxidation. In this study, valuable aromatic polycarboxylic acids were produced from Xianfeng lignite-derived residue (XLDR) through mild oxidation in green aqueous H2O2 solution. The results show that XLDR oxidation can produce benzene carboxylic acids (BCAs) and polycyclic aromatic carboxylic acids (PCACAs) in high selectivity. The BCAs are dominated by mellitic acid and benzenepentacarboxylic acid with 55.5% and 13.3% in the total yield of all group components based on the analysis with gas chromatography/mass spectrometer. Moreover, three series of PCACAs with an aliphatic ring were identified by direct analysis in a real-time ionization source coupled to a time-of-flight mass spectrometer. The BCAs and PCACAs could be generated from different kinds of aromatic structures via oxidation by OH produced from H2O2.

Rapid analysis of carboxylic acids and esters with a direct analysis in real time ion source.

Coal oxidation produces carboxylic acids (CAs), including aliphatic acids, benzoic acids, and benzenepolycarboxylic acids, which are important fine chemicals which could be used to understand the structural features of coals. However, detecting CAs usually presents great challenges due to extremely troublesome pretreatments. Therefore, it is essential to develop an analytical method for the rapid detection of CAs from coal oxidation. A series of model compounds (MCs) of oxidation products and two practical samples were investigated by direct analysis in real time time-of-flight mass spectrometry (DART-TOFMS) under three different analytical conditions (ionizing gas temperature, organic solvent, and MC concentration). Ionizing methyl benzoate, dimethyl phthalate, and dimethyl adipate produces typical ions of methyl esters, including [M-OCH3 ]+ , [M+H]+ , and [M+NH4 ]+ . In contrast, the characteristic ions generated from CAs are polymer ions, such as [2M+NH4 ]+ , [3M+NH4 ]+ , [4M+NH4 ]+ , and [5M+NH4 ]+ , indicating the strong intermolecular hydrogen-bond interaction among CAs. Results suggest that DART-TOFMS could rapidly analyze CAs or esters in coal oxidation products according to their typical ions to further gain deep insights into the coal structure.

Confirmation of Pharmaceutical Identifiers via DART-TOF-MS.

A direct analysis in real time ion source coupled with a time-of-flight mass spectrometer (DART-TOF-MS) is a suitable confirmatory technique for the analysis of pharmaceutical preparations, with accompanying reference sources for preparation markings. The DART-TOF-MS instrument allows for simple sample preparation and decreased analysis time, both crucial in a forensic laboratory setting. Differentiation can be made between active drug ingredients with the same molecular weight, such as hydrocodone and codeine, as well as pharmaceutical preparation mixtures, such as oxycodone and acetaminophen, using exact masses of the protonated molecules and fragment peaks compared to a standard.

Identification of Nitro Explosives by Direct Analysis in Real-Time Time-of-Flight Mass Spectrometry

ABSTRACTNitro compounds such as 2,4,6-trinitrotoluene, cyclotrimethylene trinitramine, and pentaerythritol tetranitrate are common ingredients of high explosives found in homeland security threats, minefields, and industrial materials. This study aims at developing a convenient surface analysis method for rapid identification of these compounds by direct analysis in real time coupled with time-of-flight mass spectrometry. The possible ionization mechanisms and fragmentation pathways using the direct analysis in real-time ionization source were developed for each compound based on the ions produced by in-source collision-induced dissociation and acquired by a time-of-flight mass spectrometer. These compounds release nitro groups and form nitroless characteristic fragments with other nitro adducts during in-source collision-induced dissociation processes. The characteristic ion [M + C2H4N3O2]− produced by cyclotrimethylene trinitramine was observed for the first time to our best knowledge. Direct analysis in real-time time-of-flight mass spectrometry has provided rapid identification of residues from various samples from explosion scenes and, therefore, is a potential powerful screening tool for criminal evidence.

Development of "Laser Ablation Direct Analysis in Real Time Imaging" Mass Spectrometry: Application to Spatial Distribution Mapping of Metabolites Along the Biosynthetic Cascade Leading to Synthesis of Atropine and Scopolamine in Plant Tissue.

Methods for the accomplishment of small-molecule imaging by mass spectrometry are challenged by the need for sample pretreatment steps, such as cryo-sectioning, dehydration, chemical fixation, or application of a matrix or solvent, that must be performed to obtain interpretable spatial distribution data. Furthermore, these steps along with requirements of the mass analyzer such as high vacuum, can severely limit the range of sample types that can be analyzed by this powerful method. Here, we report the development of a laser ablation-direct analysis in real time imaging mass spectrometry approach which couples a 213 nm Nd:YAG solid state UV laser to a direct analysis in a real time ion source and high-resolution time-of-flight mass spectrometer. This platform enables facile determination of the spatial distribution of small-molecules spanning a range of polarities in a diversity of sample types and requires no matrix, vacuum, solvent, or complicated sample pretreatment steps. It furnishes high-resolution data, can be performed under ambient conditions on samples in their native form, and results in little to no fragmentation of analytes. We demonstrate its application through determination of the spatial distribution of molecules involved in the biosynthetic cascade leading to formation of the clinically relevant alkaloids atropine and scopolamine in Datura leichhardtii seed tissue.

Identification of MDMB-FUBINACA in commercially available e-liquid formulations sold for use in electronic cigarettes

MDMB-FUBINACA (aka MDMB(N)-Bz-F), chemical name Methyl (S)-2-(1-(4-fluorobenzyl)-1H-indazole-3-carboxamido)-3,3-dimethylbutanoate, a designer drug or a new psychoactive substance (NPS), was identified in three commercially available e-liquids formulated for electronic cigarette use. The e-liquids were evaluated using direct analysis in real time ion source attached to a time of flight mass spectrometer (DART-MS) and gas chromatograph mass spectrometer (GC–MS) to identify active ingredients/drugs, flavorants, and other possible constituents. The e-liquids were also evaluated for alcohol content by headspace gas chromatography with flame ionization detector (HS-GC–FID). The aerosol produced from the e-liquids by use of an e-cigarette was analyzed by solid phase micro-extraction gas chromatography mass spectrometry (SPME–GC–MS) to ensure delivery of the active ingredient/drug. Propylene glycol, vegetable glycerin, MDMB-FUBINACA, alcohol content and a flavor profile were determined for each of the e-liquids. MDMB-FUBINACA was determined to be the major active ingredient in all three e-liquids and was successfully detected by SPME–GC–MS in the aerosol generated by a KangerTech Aerotank clearomizer/electronic cigarette.

Identification of Drugs in Parenteral Pharmaceutical Preparations from a Quality Assurance and a Diversion Program by Direct Analysis in Real-Time AccuTOFTM-Mass Spectrometry (DART-MS).

In healthcare settings drug diversion and impairment of physicians are major concerns requiring a rapid and efficient method for surveillance and detection. A Direct Analysis in Real Time ion source coupled to a JEOL AccuTOFTM time-of-flight mass spectrometer (DART-MS) method was developed to screen parenteral pharmaceutical formulations for potential drug diversion. Parenteral pharmaceutical formulations are also known as injectable formulations and are used with intravenous, subcutaneous, intramuscular and intra-articular administration. A library was created using the mass spectra data collected by a DART-MS operated in switching mode at 20, 60 and 90 V settings. This library contained 17 commonly encountered drugs in parenteral pharmaceutical formulations that included the surgical analgesic: fentanyl, hydromorphone and morphine; anesthetic: baclofen, bupivacaine, ketamine, midazolam, ropivacaine and succinylcholine; and a mixture of other drug classes: caffeine, clonidine, dexamethasone, ephedrine, heparin, methadone, oxytocin and phenylephrine. Randomly selected 200 de-identified parenteral pharmaceutical formulations containing one or more drugs were submitted for analysis to the FIRM Toxicology Laboratory at Virginia Commonwealth University Health and were screened using the DART-MS. The drug contents of the de-identified formulations were previously confirmed by a published high performance liquid chromatography (HPLC) method. The drugs in the formulations were rapidly and successfully identified using the generated library. The DART-MS and HPLC results were in complete agreement for all 200 parenteral pharmaceutical formulations.

Pharmaceutical identifier confirmation via DART-TOF

Pharmaceutical analysis comprises a large amount of the casework in forensic controlled substances laboratories. In order to reduce the time of analysis for pharmaceuticals, a Direct Analysis in Real Time ion source coupled with an accurate mass time-of-flight (DART-TOF) mass spectrometer was used to confirm identity. DART-TOF spectral data for pharmaceutical samples were analyzed and evaluated by comparison to standard spectra. Identical mass pharmaceuticals were differentiated using collision induced dissociation fragmentation, present/absent ions, and abundance comparison box plots; principal component analysis (PCA) and linear discriminant analysis (LDA) were used for differentiation of identical mass mixed drug spectra. Mass assignment reproducibility and robustness tests were performed on the DART-TOF spectra. Impacts on the forensic science community include a decrease in analysis time over the traditional gas chromatograph/mass spectrometry (GC/MS) confirmations, better laboratory efficiency, and simpler sample preparation. Using physical identifiers and the DART-TOF to confirm pharmaceutical identity will eliminate the use of GC/MS and effectively reduce analysis time while still complying with accepted analysis protocols. This will prove helpful in laboratories with large backlogs and will simplify the confirmation process.

Rapid quantification of highly polar trimethyl phosphate in wastewater via direct analysis in real-time mass spectrometry

Trimethyl phosphate (TMP) is used extensively in industrial chemical processes. Due to the high polarity and volatility, methods for its quantification in environmental samples have not been well developed. Currently, the pollution status of TMP in the environment still has not been quantitatively analyzed. This study quantifies the TMP levels in environmental water via direct analysis real-time ionization source interfaced with a triple quadrupole mass spectrometer (DART-MS/MS) with multiple reaction monitoring (MRM). The DART parameters were optimized to achieve the most TMP-sensitive MRM responses. The water samples were analyzed directly, and an isotope-labeled internal standard (ISTD) method was applied for quantification. The method exhibits significant linearity (R>0.998) in the range of 0.05–100ng/mL, with a limit of quantification (LOQ) of 50pg/mL. TMP has been accurately detected in the influent and effluent water of two municipal wastewater treatment plants and a river located in Beijing. Recovery of TMP ranged 88.0–107.6% for the spiked real water samples. The results demonstrated that TMP has been existed in environmental water, and DART-MS/MS can be used for the monitoring of the pollution status and the environmental process of TMP in environmental water.

Mass Spectrometry of Spacecraft Contamination Using Direct Analysis in Real-Time Ion Source

Spacecraft contamination was analyzed using mass spectrometry with the direct analysis in real-time ionization source. This source uses metastable helium for soft ionization and to mediate atmospheric desorption of samples into a mass spectrometer. The sampling methodology allows polymers to be assessed for the presence of vacuum labile components. Vacuum labile residues are significant sources of contamination on spacecraft optics, science instruments, and thermal control surfaces. The methodology also provides sensitive analysis of molecular contamination on spacecraft surfaces using existing spacecraft sampling procedures. This provides identification information for a wide range of molecular components including biomarker compounds.

Characterization of Biomarkers and Structural Features of Condensed Aromatics in Xianfeng Lignite

Xianfeng lignite (XL) was sequentially extracted under ultrasonication at room temperature with petroleum ether, carbon disulfide (CDS), methanol, acetone, and isometric CDS/acetone mixed solvent to afford extracts 1–5, respectively. The mixed solvent-inextractable portion was sequentially extracted with cyclohexane, benzene, 1-methylnaphthalene, methanol, and ethanol at 320 °C to afford extracts 6–10, respectively. The extracts were analyzed with a gas chromatography/mass spectrometer (GC/MS) to characterize biomarkers in XL. The biomarkers were significantly enriched in extracts 1 and 6. They can be classified into a series of n-alkanes, isoprenoid alkanes, terpenoids, n-alkenes, methyl alkanones, n-alkylbenzenes, n-alkyltoluenes, and n-alkyl-p-xylenes. The biomarker distributions provided important information on the main origin of organic matter in XL. Related mechanisms for the formation of biomarkers during coalification were discussed. The residue from sequential thermal extraction was subjected to ruthenium-ion-catalyzed oxidation along with subsequent product analyses with GC/MS and direct analysis in a real-time ionization source coupled to a time-of-flight mass spectrometer (DARTIS/TOFMS) to understand its structural features. The results show that the residue is rich in condensed aromatics (CAs) and methyl is the dominant alkyl side chain on aromatic rings. The aromatic rings in the residue are mainly connected by −(CH2)3– and −CHCH3(CH2)2–. DARTIS/TOFMS analysis suggests that CAs with alkyl-substituted biphenyl and alkyl-substituted phenylbiphenyl skeletons also exist in the residue. This investigation provides an effective approach for understanding biomarkers and the structural features of the macromolecular network in XL.

Characterizations of the Extracts from Geting Bituminous Coal by Spectrometries

Geting bituminous coal (GBC) was sequentially extracted with petroleum ether, carbon disulfide (CDS), methanol, acetone, and isometric CDS/acetone mixed solvent at room temperature to afford extracts 1–5 (E1–E5) and residue. Detailed characterizations of the extracts were performed with a gas chromatography/mass spectrometer (GC/MS), Fourier transform infrared (FTIR) spectrometer, and direct analysis in real-time ionization source (DARTIS) coupled to an ion-trap mass spectrometer (ITMS). GBC and its residue were also analyzed with the FTIR spectrometer. Particle sizes of the residue were significantly reduced compared to those of GBC according to the observation with a scanning electron microscope. Arenes with 1–4 rings and more condensed arenes were enriched into E1 and E2, respectively, while more heteroatom-containing organic species were detected in other extracts, especially in E3 and E4 according to GC/MS analysis. The extracts, especially E1–E4, contain more aliphatic moieties and less aromatic moi...

Characterization of blood in an encrustation on an African mask: spectroscopic and direct analysis in real time mass spectrometric identification of haem

Prior to exhibiting an African Komo mask from the collections of the Detroit Institute of Arts, a multianalytical approach was undertaken to characterize the flaking encrusted coating on the surface of the mask. Preliminary XRF and FTIR examination of the coating on the Komo mask revealed the presence of significant quantities of iron and protein, possibly indicating the presence of blood. Raman spectroscopy showed evidence for the porphyrin structure of haem as well. To confirm that blood was indeed present in the coating, we developed a novel method for identifying the haem moiety from blood by use of in situ methylation and direct analysis in real time mass spectrometry (DART-MS). Following a denaturing step with formic acid, the resulting solution was combined with an excess of phenyltrimethylammonium hydroxide to promote desorption, applied to a melting point tube, and placed into the direct analysis in real time ion source gas stream at 550 °C. The permethylated haem ion (m/z 644.208) from myoglobin, haemoglobin, fresh blood, and blood aged in the laboratory for 10 years was readily observed above the background. By the described DART-TOF-MS method, permethylated haem was positively identified in the mask coating, confirming the presence of blood. This method has obvious utility in forensic science beyond that for identifying blood incorporated in cultural heritage materials.

Confined direct analysis in real time ion source and its applications in analysis of volatile organic compounds of Citrus limon (lemon) and Allium cepa (onion)

The DART (direct analysis in real time) ion source is a novel atmospheric pressure ionization technique that enables efficient ionization of gases, liquids and solids with high throughput. A major limit to its wider application in the analysis of gases is its poor detection sensitivity caused by open-air sampling. In this study, a confined interface between the DART ion source outlet and mass spectrometer sampling orifice was developed, where the plasma generated by the atmospheric pressure glow discharge collides and ionizes gas-phase molecules in a Tee-shaped flow tube instead of in open air. It leads to significant increase of collision reaction probability between high energy metastable molecules and analytes. The experimental results show that the ionization efficiency was increased at least by two orders of magnitude. This technique was then applied in the real time analysis of volatile organic compounds (VOCs) of Citrus Limon (lemon) and wounded Allium Cepa (onion). The confined DART ion source was proved to be a powerful tool for the studies of plant metabolomics.

Study of Mechanism of Ionization Assisted by Methylation in Direct Analysis in Real Time Ion Source

Direct analysis in real time ion source (DART) has been applied to the rapid analysis of solid, liquid and gaseous samples. The compounds with either high volatility or high proton affinity are favorable for DART analysis. However, a lot of natural products such as ginsenosides and ginseng oligosaccharides are difficult to be directly ionized by DART due to their low volatility and proton affinity. Derivatization is very necessary in the analysis of the compounds with low volatility and proton affinity. Tetramethylammonium hydroxide (TMAH) is a frequently used methylation reagent which can be applied to improve the volatility of low volatile compound in GC-MS. In the current work, TMAH was introduced to assist the ionization of ginsenoside and ginseng oligosaccharide in DART. Small amount of ginsenoside standard or ginseng oligosaccharide powder was collected on the end of melting point tubes respectively. Then 5 mu L of liquid from a solution containing 25% solution of TMAH dissolved in MeOH was applied to elute the surface of each melting point tube. Finally, all the end of melting point tubes containing sample powder and TMAH were put on a stainless holder for DART analysis. The solvents were flash evaporated in the DART source at 400 degrees C and the signals of methylated analytes were detected. The mechanism of methylation and ionization in DART was elucidated from the aspects of condensed and gas phase. On the one hand, the methylation enhanced volatility of analytes, on the other hand, a N(CH3)(3)H+ ion was generated to assist the ionization of methylated analytes. Incomplete and complete methylation is the major reaction of ginsenoside, but hypermethylation occurred in ginseng oligosaccharide with the increase of number of hydroxyls. The results showed that the synergy of methylation reaction both in condensed phase and gas phase is the fundamental reason of the generation of methylated ions. The methylation in condensed phase is governed by necleophilic reaction, and radical reaction is the major reaction in gas phase.