Recorded Mass Spectra Research Articles

High-resolution mass spectrometry for molybdenum speciation in sulfidic waters

High resolution electrospray ionization mass spectrometry (ESI-HRMS) was used to study the speciation of molybdenum in interaction with sulfide and chloride. While reactions between molybdate and sulfide lead to creation of four conventional thiomolybdate species (MoO3S2−, MoO2S22−, MoOS32−, MoS42−), chemical formula assignment of recorded mass spectra confirmed the presence of intermediate thiomolybdate compounds (MoO3S22−, MoO2S32−, MoOS42−, MoS52−, MoS62−) and thio-chloro-molybdate compounds (MoO3Cl−, MoO2SCl−, MoOS2Cl−, MoOS3Cl−). Two of the intermediate thiomolybdate compounds were previously suggested theoretically, and this study provides analytical support for the existence of these compounds. Fast ESI-HRMS analysis has allowed us to conduct a highly-resolved short-term kinetic study of these reactions, and we suggest that the reactivity between molybdate and sulfide is more complex than previously thought, particularly during the first 24 h of interaction. Also, the solution composition will impact reaction pathways, and different outcomes found in the literature may arise from choices of ionic strength and pH adjusting agents in previous studies . The occurrence of the thio-chloro-molybdate species detected in this study should be implemented in future Mo speciation models to better assess Mo reactivity in sulfidic waters and reducing environments.

Ion Manipulation in Open Air Using 3D-Printed Electrodes.

Ambient ionization techniques provide a way to sample materials via creation of ions in the air. However, transferring and focusing of these ions is typically done in the reduced pressure environment of the mass spectrometer. Spray-based ambient ionization sources require relatively large distances between the source and mass spectrometer inlet for effective desolvation, resulting in a small fraction of the ions being collected. To increase the efficiency of ion transfer from atmosphere to vacuum, 3D-printed focusing devices made of conductive carbon nanotube doped polymers have been designed and evaluated for ion focusing in air. Three main classes of electrodes are considered: (i) conic section electrodes (conical, ellipsoidal, and cylindrical), (ii) simple conductive and non-conductive apertures, and (iii) electrodes with complex geometries (straight, chicane, and curved). Simulations of ion trajectories performed using the statistical diffusion simulation (SDS) model in SIMION showed a measure of agreement with experiment. Cross-sectional images of ion beams were captured using an ion detecting charge-coupled device (IonCCD). After optimization, the best arrangements of electrodes were coupled to an Agilent Ultivo triple quadrupole to record mass spectra. Observations suggest that electrode geometry strongly influences ion trajectories in air. Non-conductive electrodes also assisted in focusing, due to charge buildup from ion deposition. We also observed minimal spreading of the ion packet after exiting the focusing electrodes indicating that atmospheric collisions do not reduce collimation of the beam. The study suggests that high pressures need not be viewed as a hindrance to ion transport, but as a potentially useful force.

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS).

Sesquiterpenes are structurally diverse, potent flavoring substances that significantly influence the aroma profile of grapes (Vitis vinifera L.) at the time of physiological ripening. To investigate these natural compounds, freshly harvested, ripe berries of the red wine variety Lemberger (Vitis vinifera subsp. vinifera L.) were analyzed using comprehensive two-dimensional gas chromatography (GC×GC) coupled to a time-of-flight mass spectrometer (TOF–MS) after headspace-solid phase microextraction (HS-SPME). The identification of structurally complex natural compounds, such as sesquiterpenes from fruits and vegetables, is often reported as “tentative”, as authentic standards are not commercially available for most of the analytes. For this reason, feeding experiments (in vivo labeling) were carried out using the stable isotope-labeled precursors [5,5-2H2]-1-deoxy-ᴅ-xylulose (d2-DOX) and [6,6,6-2H3]-(±)-mevalonolactone (d3-MVL) to clearly identify the volatiles. Based on the recorded mass spectra of the unlabeled and deuterated compounds, mechanisms for sesquiterpene formation in V. vinifera could be proposed and already known pathways could be confirmed or disproved. For example, the HS-SPME–GC×GC–TOF–MS measurements of fed sample material showed that the tricyclic sesquiterpene hydrocarbons α-copaene, β-copaene, α-cubebene, β-cubebene and the bicyclic δ-cadinene were biosynthesized via (S)-(−)-germacrene D rather than via (R)-(+)-germacrene D as intermediate.

Comparison of high-performance thin-layer with overpressured layer chromatography combined with direct bioautography and direct analysis in real time mass spectrometry for tansy root

Bioactive polyacetylenes in tansy (Tanacetum vulgare L.) root extract were separated by overpressured layer chromatography (OPLC) with better resolutions than achievable by capillary flow high-performance thin-layer chromatography (HPTLC). OPLC enabled a longer development distance in a shorter time (16 cm, 7 min) in comparison to conventional HPTLC (7 cm, 16 min). OPLC separations on HPTLC plates with spherical particles resulted in higher resolutions than on such with irregular particles. A slight distortion of zones sometimes occurred that could be eliminated by sonication of the mobile phase through removal of the dissolved air. However, zone distortion did not diminish the meaning of the qualitative outcome. The combination of OPLC with direct bioautography and direct analysis in real time-high resolution mass spectrometry (DART-HRMS) led to the determination of the individual polyacetylenes responsible for the diverse effects. In each recorded mass spectrum, the basepeak was the respective protonated molecule. The assignments confirmed the results of a previous study, however, compounds TR5a (tetradeca-2,4,6-triine-8-en-12-one) and TR5b (trans-2-(2,4-hexadiynylidene)-1,6-dioxaspiro[4,5]dec-3-ene) that were not separable by HPTLC were partially separated by OPLC. Thus, it was proven that TR5b was not an oxidation product of TR5a and thus not formed as artefact during the HPTLC-DART-HRMS analysis, but originally present in the sample.

High-throughput determination of vitamin E in extra virgin olive oil by paper spray tandem mass spectrometry.

Extra virgin olive oil provides an important intake of α-tocopherol, which is part of vitamin E complex. A fast analytical method for its quantification, based on paper spray mass spectrometry, has been developed. The methodology possesses the ability to record mass spectra without sample preparation or preseparation steps. The experiments were performed in Multiple Reaction Monitoring scan mode; in particular, the transitions m/z 429 → m/z 163 for α-tocopherol and m/z 435 → m/z 169 for the labeled internal standard were monitored, in order to obtain the greatest specificity and the best sensitivity. The accuracy of the method was tested analyzing spiked samples prepared at concentrations within the dynamic range of the calibration curve, which returned values near 100%. Furthermore, good values of LOQ and LOD were obtained, demonstrating that this approach can be applied for a rapid screening of tocopherols in different vegetable oils. The results were compared with analyses performed by traditional chromatographic methods. Graphical abstract.

Chemometric prediction of swelling potentials of aviation fuels towards elastomers using various spectroscopic data

This work presents the development of chemometric models, based on spectroscopic data, predicting the swelling potentials of aviation fuels towards three ready for use acrylonitrile-butadiene-rubber (NBR) types exhibiting acrylonitrile contents of 18, 28 and 39%. For this purpose quaternary model substance mixtures, containing compounds, which are typical for aviation fuels were prepared. As a second set, exclusively aliphatic synthetic aviation fuels were blended with varying amounts of an aromatic fraction. After immersion in the prepared fluids, the extent of the equilibrium mass uptakes by the elastomers was determined and interpreted in terms of different mixtures’ formulations. UV/Vis- and infrared (IR) spectra were collected of all liquids. Additionally, gas chromatography/mass spectrometry (GC/MS) analyses were carried out. Based on the obtained data, sum mass spectra, which are basically a merging of all recorded mass spectra of a chromatographic run, were generated. Spectroscopic data and swelling characteristics were correlated using partial least squares regression (PLS). Here two different models, based on both training sets were established for each spectroscopic method. Obtained regression coefficients underwent a detailed evaluation to get a better understanding of factors influencing the prediction of swelling potentials. It was found, that they reflect well-known relations between the composition of a liquid, represented by specific spectral information and their corresponding swelling potential. The models were validated by estimating swelling potentials of two commercial jet fuels Jet A-1 and ReadiJet. Infrared spectra pose the most reliable base for the chemometric prediction of swelling characteristics of NBR containing 18% acrylonitrile with prediction errors of 5 and 2% for Jet A-1 and ReadiJet, respectively. Also sum mass spectra allow a relatively accurate estimation.

A microscale solid-phase microextraction probe for the in situ analysis of perfluoroalkyl substances and lipids in biological tissues using mass spectrometry.

The simultaneous analysis of perfluoroalkyl substances (PFASs) and lipids in biological tissues is of importance, especially for in situ and microscale analysis, because it provides significant information to understand the relevance of content, composition, and distribution of lipids to the bioaccumulation of PFASs as well as lipid metabolism affected by the biotoxicity of PFASs. In this study, we report the development of a novel ambient mass spectrometry method for the rapid, in situ, and microscale analysis of PFASs and lipids simultaneously in biological tissues for the investigation of their biological correlation. A microscale solid-phase microextraction (SPME) probe with a probe-end diameter of several-μm was employed for in situ and microscale sampling of biological tissues after PFAS exposure. The SPME probe showed a desirable capacity for the enrichment of PFASs and lipid species simultaneously. After sampling and extraction, the loaded SPME probe was directly applied for nanoESI-MS analysis under ambient and open-air conditions. A high-resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometer operated in the field-induced mode was introduced to record mass spectra using fast polarity switching between positive and negative ion detection. Most of the lipid species were recorded in the positive ion mass spectrum, and PFASs were recorded in the negative ion mass spectrum. By using the developed method, the in situ analysis of PFASs and lipids in the muscle, brain, heart, kidney, liver, and intestine of zebrafish was realized. In addition, simultaneously imaging PFASs and lipids in individual Daphnia magna was successfully achieved for the investigation of their biological correlation.

A New Post-Chromatographic Derivatization Approach to the Identification of Alcohols and Phenols in Complex Mixtures by a Combination of Planar Chromatography and Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

A simple and suitable approach to the post-chromatographic derivatization in the analysis of alcohol and phenols mixtures by a combination of thin-layer chromatography and MALDI mass spectrometry was proposed for the first time. The chemical modification of analytes was accomplished by the treatment of eluted zones on thin-layer chromatograms by 3-bromopropionyl chloride in the presence of an excess of a base (pyridine or triethylamine). The resulting derivatives contained a residue with a constant charge (ammonium fragment) that ensures the efficient desorption of the derivatized analytes from the sorbent layer during MALDI. It was shown that the proposed approach allows the recording of mass spectra with a high signal/noise ratio and the detection of alcohols and phenols of different structures. The reproducibility of such MALDI mass spectra is rather high, which predetermines a possibility of building chromatogram curves using total or selected ion current and, hence, their visualization and treatment on the quantitative level.

The role of carrier gas in cluster formation in methane supersonic jets

The influence of a monatomic carrier gas on cluster formation in supersonic methane jets is studied. The formation of methane clusters in a mixture with condensed argon and non-condensable helium with the same gas-dynamic parameters is then compared. It is shown that the methane clusters’ formation intensity is extremely low both within a jet of pure methane, and in a mixture with carrier argon. The methane condensation process dependence on the properties of a carrier gas and the methane volume fraction in the mixture at the selected gas dynamic parameters of the flow is demonstrated. The effect of dissociative methane ionization and the fragmentation of methane clusters in the mass spectrometer detector on the recorded mass spectrum is established. The cluster methane ions protonation and the increase in their fraction with increasing clusters are recorded. Finally, magic numbers for methane clusters are found.

Monte Carlo Simulation of Low-Count Signals in Time-of-Flight Mass Spectrometry and Its Application to Single-Particle Detection.

Many modern time-of-flight mass spectrometry (TOFMS) instruments use fast analog-to-digital conversion (ADC) with high-speed digitizers to record mass spectra with extended dynamic range (compared to time-to-digital conversion). The extended dynamic range offered by ADC detection is critical for accurate measurement of transient events. However, the use of ADC also increases the variance of the measurements by sampling the gain statistics of electron multipliers (EMs) used for detection. The influence of gain statistics on the shape of TOF signal distributions is especially pronounced at low count rates and is a major contributor to measurement variance. Here, we use Monte Carlo methods to simulate low-ion-count TOFMS signals as a function of Poisson statistics and the measured pulse-height distribution (PHD) of the EM detection system. We find that a compound Poisson distribution calculated via Monte Carlo simulation effectively describes the shape of measured TOFMS signals. Additionally, we apply Monte Carlo simulation results to single-particle inductively coupled plasma (sp-ICP) TOFMS analysis. We demonstrate that subtraction of modeled TOFMS signals can be used to quantitatively uncover particle-signal distributions buried beneath dissolved-signal backgrounds. On the basis of simulated signal distributions, we also calculate new critical values ( LC) that are used as decision thresholds for the detection of discrete particles. This new detection criterion better accounts for the shape of dissolved signal distributions and therefore provides more robust identification of single particles with ICP-TOFMS.

Spectral skewing in gas chromatography–mass spectrometry: Misconceptions and realities

In the field of gas chromatography–mass spectrometry, linear quadrupole instruments remain the most popular. Quadrupole mass spectrometers are scanning instruments. It means that ions with different m/z values pass through the quadrupole sequentially. When analyte concentration changes during scan period, recorded mass spectrum is distorted. This phenomenon is called spectral skewing. There are two misconceptions associated with the spectral skewing: (1) the spectral skewing can affect the results of library search; (2) bilinear chemometric methods are often applied to skewed (distorted) GC/MS data to perform automatic data processing. We attempt to clarify these misconceptions. We can conclude that even strong distortion of mass spectrum (caused by the spectral skewing) practically does not change efficiency of automatic search against mass spectral database. On the other hand, even minor distortion of data (caused by the spectral skewing) can significantly distort results of automatic data processing (especially in the case of minor components). Interactive Excel files (presented in Supplementary material) illustrate our findings.

Screening of psychoactive components in fresh khat using direct analysis in real time-time of flight-mass spectrometry

Background: Khat (Catha edulis Forsk) is a shrub endemic to East Africa and the Arabian Peninsula that is widely consumed for its psychoactive properties. Due to the increase of illicit drugs consumption in the world, there is a need for fast investigation techniques in order to rapidly characterize the huge number of seized samples. In the recent years, direct analysis in real-time mass spectrometry (DART-MS) proved to be a useful and convenient method which allows recording mass spectra of various samples without any preparation. Objectives: The present work describes a convenient procedure for rapid characterization of fresh Khat samples by identification of cathinone and cathine which are the most active constituents in different parts of the plant. Materials and Methods: A fresh sample of C. edulis was cut into small pieces with separation of leaves and stems; each part was investigated using DART-time-of-flight (ToF)-MS. The fresh samples were submitted to a stream of hot helium as vaporization and ionization gas, without any extraction or prior treatment. Results: The obtained spectra showed many peaks corresponding to the mass range from 100 to 600 Da. Cathinone and cathine which are known to be the main psychoactive components in C. edulis were found in all parts of the fresh samples; their protonated peaks appeared at 150 and 152 Da, respectively. The peak intensity of these two characteristic alkaloids was notably different between leaves and stems; it roughly decreased from lower to upper leaves, while their highest content was obtained in the upper stem. Conclusion: The present work showed that DART-ToF-MS is a powerful tool for fast investigation of real samples, particularly in the field of forensic sciences.

New Approaches to the Application of DART Mass Spectrometry Coupled with Planar Chromatography for the Analysis of Mixtures of Organic Compounds

A desorption cell for TLC/DART mass spectrometry is developed. An analysis of mixtures of pharmaceutical substances has shown that the proposed approach can improve the sensitivity of the method and achieve the reproducibility of the recorded mass spectra and selected ion chromatograms.

Gas analysis using a MEMS linear time-of-flight mass spectrometer

This paper presents the optimization of the ionization, extraction and focalization of our new generation of microfabricated time-of-flight mass spectrometer (μ-TOF). Using electron impact ionization, we show ionization efficiencies in the range of 1.10−6 ion/neutral, which is in the same order of magnitude as macroscale electron impact ionizers. A generated ion current in the range of a few tens of nanoamperes lead to an ionization yield around 0.1%, in the same range as the best microfabricated ionizers. The extracted and focalized ion beam is collected in a Micro Channel Plate detector and used to record mass spectra. Using decreasingly concentrated gas mixtures, we show the ability of the linear microfabricated time-of-flight mass spectrometer to detect up to 100ppm of alkanes in helium. This work pulls the μ-TOF one step closer towards a fully integrated portable analytical system.

PHYTOCHEMICAL STUDIES AND GC-MS ANALYSIS OF SPERMADICTYON SUAVEOLENS ROXB

Objective: The present study was performed to identify the phytochemical constituents of leaves and flowers of a plant Spermadictyon suaveolens extracted with four different solvents.Methods: Dried and powdered samples were subjected to soxhlation based on the polarity of the solvents. The extracts were scanned using Ultra Violet-visible (UV-Vis) spectrophotometry with the wavelength ranging from 200–800 nm by comparing the absorption spectrum with the spectra of known compounds, Fourier Transform Infrared (FT-IR) spectrometry was used to find out the functional groups of the compounds and GC-MS system consisting of a Perkin Elmer Technologies Model Clarus 680 GC equipped with Clarus 600 (EI) was used to identify the metabolites by matching their recorded mass spectra with the standard mass spectra from National Institute of Standards and Technology (NIST05. LIB) libraries provided by the software of the GCMS system (TurboMass version 5.4.2).Results: The phytochemical tests indicated the presence of carbohydrates, alkaloids, flavonoids, phenols, tannins, saponins and terpenoids from the chloroform extract of leaves and flowers. UV-visible spectrophotometer results indicated a wavelength range between 230–660 nm for the flower and leaf extracts for major peaks. FT-IR analysis indicated major functional groups such as aromatic, primary, secondary and aliphatic amines, alkanes, carboxylic acids and amides. GC-MS analysis results revealed major bioactive compounds in the crude extracts.Conclusion: Presence of secondary metabolites has been identified from the phytochemical studies. Many phyto-compounds have been identified from the leaves and flowers of using GC-MS analysis. Hence, this medicinal plant may be used as a source for treating many diseases.

On the impossibility of double focusing in combined electric and magnetic fields homogeneous in Euler’ terms

The use of Euler’s homogeneous electric and magnetic fields can be a good basis for designing static mass spectrometers capable of operating in a spectrographic mode and enabling recording of mass spectra with a wide mass range in one measurement. It is proved mathematically that, when combined Euler’s homogeneous electric and magnetic fields are used to design a single-cascade mass-spectrometer, the double focusing mode cannot be achieved practically along the entire focal line. It is demonstrated that the use of mass spectrographic schemes in which the electric stage and the magnetic stage are separated is an inevitable solution in the creating of a mass spectrograph with high analytical performance.

Carbon nanocoatings: A new approach to recording mass spectra of low-molecular compounds using surface-assisted laser desorption/ionization mass spectrometry

A simple and rapid approach to obtaining target plates for the investigation of low-molecularweight compounds by surface-assisted laser desorption/ionization (SALDI) mass spectrometry is proposed. It consists in the vacuum sputtering of a carbon layer with a thickness of about 50 nm onto a metal surface. The resulting coatings are characterized by homogeneity, hydrophobicity, and high mechanical strength, which eliminates a possibility of mass spectrometer contamination. A comparison of the SALDI mass spectra of test compounds recorded using conventional carbon materials and carbon nanocoatings demonstrates advantages of the last named materials, such as high spectral resolution and the absence of spectral interferences at low m/z values.

Rapid discrimination of bergamot essential oil by paper spray mass spectrometry and chemometric analysis.

A novel approach for the rapid discrimination of bergamot essential oil from other citrus fruits oils is presented. The method was developed using paper spray mass spectrometry (PS-MS) allowing for a rapid molecular profiling coupled with a statistic tool for a precise and reliable discrimination between the bergamot complex matrix and other similar matrices, commonly used for its reconstitution. Ambient mass spectrometry possesses the ability to record mass spectra of ordinary samples, in their native environment, without sample preparation or pre-separation by creating ions outside the instrument. The present study reports a PS-MS method for the determination of oxygen heterocyclic compounds such as furocoumarins, psoralens and flavonoids present in the non-volatile fraction of citrus fruits essential oils followed by chemometric analysis. The volatile fraction of Bergamot is one of the most known and fashionable natural products, which found applications in flavoring industry as ingredient in beverages and flavored foodstuff. The development of the presented method employed bergamot, sweet orange, orange, cedar, grapefruit and mandarin essential oils. PS-MS measurements were carried out in full scan mode for a total run time of 2 min. The capability of PS-MS profiling to act as marker for the classification of bergamot essential oils was evaluated by using multivariate statistical analysis. Two pattern recognition techniques, linear discriminant analysis and soft independent modeling of class analogy, were applied to MS data. The cross-validation procedure has shown excellent results in terms of the prediction ability because both models have correctly classified all samples for each category. Copyright © 2016 John Wiley & Sons, Ltd.

A mass spectrometer with a membrane interface for oil concentration monitoring in seawater

An immersion mass spectrometer with a membrane interface was used for oil detection and oil concentration measurements in seawater by measuring in situ the concentrations of three hydrocarbons: benzene, toluene, and xylene in the region of the specialized Primorsk oil loading seaport in the Gulf of Finland. The recorded mass spectra demonstrated the possibility of measuring the oil concentration in seawater and determining the grade of oil products. The use of a mass spectrometer with a membrane separator interface allows measurements of hydrocarbon concentration with high accuracy, which is currently not provided in commercially available monitors.

Simultaneous detection of positive and negative secondary ions

A secondary ion mass spectrometer (SIMS) instrument is described that is configured with two SIMS detectors that are both low-field extraction, quadrupole-based filters. Secondary ions are generated by sputtering with a liquid-metal ion gallium source and column of the type that is common on two-beam electron microscopes. The gallium ion beam, or focused ion beam achieves sub-100 nm focus with a continuous current of up to 300 pA. Positive secondary ions are detected by one SIMS detector, and simultaneously, negative secondary ions are detected by the second SIMS detector. The SIMS detectors are independently controlled for recording mass spectra, concentration depth profiles, and secondary ion images. Examples of simultaneous positive and negative SIMS are included that demonstrate the advantage of this facility for surface analysis and depth profiling. The SIMS secondary ion collection has been modeled using the ray tracing program simion (“simion”, Scientific Instrument Services, Inc., Ringoes, NJ, 08551-1054, see http://www.simion.com) in order to understand the interaction of the secondary ions of opposite polarities in the extraction volume for the purpose of optimizing secondary ion collection.