Linear Trap Mass Spectrometer Research Articles

The Magnesium Dication and Water Synergistically Promote the Protonolysis of Two of the B-C Bonds in the Tetraphenylborate Anion.

Analytes are sampled from both solution phase and gas-phase environments during the ESI process, and thus, the mass spectrum that is measured can reflect both solution and gas-phase conditions. In the gas-phase regime, ion-molecule reactions can influence the types of ions that are observed. Herein, the synergistic effects of a Lewis acid (Mg2+) and background water are shown to lead to protonolysis of two of the B-C bonds of the tetraphenylborate ion in the gas phase, giving rise to different ions at different reaction times in ESI-MS/MS experiments in a linear ion trap mass spectrometer. At short reaction times (1 ms), the expected adduct [Mg(BPh4)]+ is observed. At 10 ms, [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ are observed. At 100 ms, the water adducts [(HO)2Mg(BPh2)(H2O)]+ and [(HO)2Mg(BPh2)(H2O)2]+ appear, and these become the dominant ions at longer reaction times. DFT calculations provide a plausible explanation as to why only [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ but not [(HO)3Mg(BPh)]+ are observed.

Development of a portable gas chromatography linear ion trap mass spectrometer (GC-LIT-MS) for VOCs analysis in water

The detection of volatile organic compounds (VOCs) in water faces challenges due to the presence of complex matrix interferences and low concentration. This paper presented a portable gas chromatography linear ion trap mass spectrometer (GC-LIT-MS) coupled with dynamic headspace sampling (DHS) system for sensitive and rapid on-site analysis of VOCs in water. The instrument weighs 18 kg and has compact dimensions of 43 cm × 35 cm x 20 cm, offering portability and convenience. A low thermal mass (LTM) chromatographic column, utilizing resistive heating, enables rapid heating and cooling within the runtime of GC. The linear ion trap, for the first time, has been integrated as a mass analyser in portable gas chromatography-mass spectrometer (GC-MS). Its ability to store a greater number of ions within the trap expands the dynamic range of the instrument. The influence of dynamic headspace injection conditions on the purging efficiency of VOCs was investigated and the equilibrium temperature was optimized. The GC-LIT-MS method was demonstrated to be capable to identify and separate 55 VOCs in water within 4 min, with most of them exhibiting detection limits of less than 1 μg L−1. The calibration of 4 VOCs with concentrations ranged from 2 parts per million (ppm) to 200 ppm showed excellent linearity (R2 > 0.99) and dynamic range more than five orders of magnitude. Resolution superior to unit mass was achieved within the range of 15 AMU to 550 AMU.

Linear Ion Trap Mass Spectrometer (LITMS) Instrument Field and Laboratory Tests as Part of the ARADS Field Campaigns.

The highly compact Linear Ion Trap Mass Spectrometer (LITMS), developed at NASA Goddard Space Flight Center, combines Mars-ambient laser desorption-mass spectrometry (LD-MS) and pyrolysis-gas chromatography-mass spectrometry (GC-MS) through a single, miniaturized linear ion trap mass analyzer. The LITMS instrument is based on the Mars Organic Molecule Analyser (MOMA) investigation developed for the European Space Agency's ExoMars Rover Mission with further enhanced analytical features such as dual polarity ion detection and a dual frequency RF (radio frequency) power supply allowing for an increased mass range. The LITMS brassboard prototype underwent an extensive repackaging effort to produce a highly compact system for terrestrial field testing, allowing for molecular sample analysis in rugged planetary analog environments outside the laboratory. The LITMS instrument was successfully field tested in the Mars analog environment of the Atacama Desert in 2019 as part of the Atacama Rover Astrobiology Drilling Studies (ARADS) project, providing the first in situ planetary analog analysis for a high-fidelity, flight-like ion trap mass spectrometer. LITMS continued to serve as a laboratory tool for continued analysis of natural Atacama samples provided by the subsequent 2019 ARADS final field campaign.

SR-Unet: A Super-Resolution Algorithm for Ion Trap Mass Spectrometers Based on the Deep Neural Network.

The mass spectrometer is an important tool for modern chemical analysis and detection. Especially, the emergence of miniature mass spectrometers has provided new tools for field analysis and detection. The resolution of a mass spectrometer reflects the ability of the instrument to discriminate between adjacent mass-to-charge ratio ions, and the higher the resolution, the better the discrimination of complex mixtures. Quadrupole ion traps are generally considered as a low-resolution mass spectrometry method, but they have gained wide attention and development in recent years because of their suitability for miniaturization and high qualitative capability. For an ion trap mass spectrometer, the mass sensitivity and resolution can be mutually constrained and need to be balanced by setting an appropriate scanning speed. In this study, a super-resolution U-net algorithm (SR-Unet) is proposed for ion trap mass spectrometry, which can estimate the possible ions from the overlapping ion peaks of low-resolution spectra and improve the equivalent resolution while ensuring sufficient sensitivity and analysis speed of the instrument. By determining the mass spectra of a linear ion trap mass spectrometer (LTQ XL) in Turbo and Normal scan modes, the same unit mass resolution as that at a scan speed of 16,667 Da/s was successfully obtained at 125,000 Da/s. Also, the experiments demonstrated that the algorithm is capable of the mass-to-charge ratio and instrument migration. SR-Unet can be migrated and applied to a miniature mass spectrometer for cruise detection of volatile organic compounds (VOCs), and the identification of VOC species in Photochemical Assessment Monitoring Stations (PAMS) was improved from 31 to 50 species with the same monitoring and analysis speed requirement. Further, super-unit mass resolution peptide detection was achieved on a miniature mass spectrometer with the help of the SR-Unet algorithm, which reduced the full width at half-maxima (FWHM) of bradykinin divalent ions (m/z 531) from 0.35 to 0.15 Da at a scan speed of 375 Da/s and improved the equivalent resolution to 3540. The proposed method provides a new idea to enhance the field mixture detection capability of miniature ion trap mass spectrometers.

Characterizing phase transitions for titan's surface molecules: Implications for Dragonfly

The potential commonality of organic synthesis and prebiotic processes on the surface of Titan and primitive Earth makes Saturn's largest moon an indispensable location to seek answers for the origins of life on Earth and elsewhere. NASA's New Frontiers Mission, Dragonfly, is set to arrive on Titan's surface in the mid-2030s. Two of the main scientific goals of the Dragonfly mission are to identify chemical components and potential processes responsible for the production of biologically relevant compounds, and to search for potential biosignatures. To address these mission goals, Dragonfly is equipped with a linear ion trap mass spectrometer, called the Dragonfly Mass Spectrometer, or DraMS. This instrument will measure the molecular composition of Titan's surface at various locations inside and near Selk Crater, where prebiotic chemistry is expected to have occurred. Some molecules of interest on Titan's surface are thought to be sensitive to phase changes within the expected range of the sample handling chain, 94–165 K and 0.04–1.5 bar. A large abundance of such materials may therefore impact the capture efficiency and physical properties of the sampled materials within the DraMS system. In this work, we explore the potential for some of the hypothesized abundant organic molecules to be induced into phase transitions during the end-to-end sampling process by DraMS.

Analysis for disulfide bonds in polypeptide sequences based on ultraviolet photodissociation combined with linear ion trap mass spectrometry

The analysis of dissociation products of disulfide bonds in peptide sequences has been increasingly applied in various fields. Ion dissociation is typically performed by tandem mass spectrometry, in which the overall molecular weight is determined during the first stage and the protein sequence and structure are obtained by dissociation during the second stage. However, conventional dissociation methods have some disadvantages, such as insufficient dissociation efficiency, and low product signals and varieties. Ultraviolet photodissociation (UVPD) is a rapid, efficient, and practical dissociation method for protein analysis, which excites the biomolecule skeleton and then directly excites the molecules, forming the excited states within microseconds. Although the development of mass spectrometer platforms coupled with UVPD has been reported to date, most of these studies have focused on the application of UVPD in mass spectrometry (MS). Discussions on the experimental setup for UVPD lasers, including the trigger process of the ultraviolet (UV) laser, the timing sequence of the entire dissociation and detection process, and their influence on dissociation, are limited. Therefore, an instrument platform was developed with a linear ion-trap mass spectrometer and an excimer laser to achieve UVPD by adjusting the laser trigger signal. The platform dissociated the disulfide bond of the amino acid sequence ARACAKA-ECG into two characteristic valence states (m/z = 498 and 332), and their highest intensities were obtained by optimizing the experimental conditions of the platform. The dissociation results of UVPD showed the characteristic peaks of ARACAKA (m/z 345) that were produced by disulfide bond cleavage, but these peaks were not detected by collision-induced dissociation (CID). Therefore, it was confirmed that the developed platform realized UVPD of the disulfide bond of the amino acid sequence of the polypeptide. Moreover, the developed platform provides a reference for the implementation of UVPD for peptide sequencing.

LC-MS/MS-MS3 for the Determination and Quantification of Δ9-Tetrahydrocannabinol and Metabolites in Blood Samples.

Due to the high prevalence of cannabinoids in forensic toxicology analysis, it is crucial to have an efficient method that allows the use of a small sample amount and that requires a minimal sample preparation, for the determination and quantification of low concentrations. A simple, highly selective and high throughput liquid chromatography tandem mass spectrometry methodology (LC-MS/MS-MS3) was developed for the determination and quantification of ∆9-tetrahydrocannabinol (THC), 11-hydroxy-∆9- tetrahydrocannabinol (THC-OH) and 11-nor-9-carboxy-∆9-tetrahydrocannabinol (THC-COOH), in blood samples. Chromatographic analysis of THC, THC-OH, and THC-COOH and their deuterated internal standards was preceded by protein precipitation (PPT) of 0.1 mL of blood samples with acetonitrile. Chromatographic separation was achieved by use of an Acquity UPLC® HHS T3 (100 mm x 2.1mm i.d., 1.8 μm) reversed-phase column, using a gradient elution of 2 mM aqueous ammonium formate, 0.1% formic acid, and methanol at a flow rate of 0.4 mL/min, with a run time of 10 minutes. For the MS/MS-MS3 analysis, a SCIEX QTRAP® 6500+ triple quadrupole linear ion trap mass spectrometer was used via electrospray ionization (ESI), operated in multiple reaction monitoring (MRM) and linear ion trap mode (MS3). The method was validated in accordance with internationally accepted criteria and guidelines, and proved to be selective and linear between 0.5-100 ng/mL (r2>0.995). The lower limits of quantification (LLOQ) corresponded to the lowest concentrations used for the calibration curves. The coefficients of variation obtained for accuracy and precision were <15%. The mean recoveries were between 88.0-117.2%, for the studied concentration levels (1 ng/mL, 5 ng/mL and 50 ng/mL). No significant interfering compounds, matrix effects or carryover were observed. The validated method provides a sensitive, efficient and robust procedure for the quantification of cannabinoids in blood, using LC-MS/MS-MS3 and a sample volume of 0.1 mL. This work is also a proof of concept for using LC-MS3 technique to determine drugs in biological samples.

Differentiation of the Aziridine Functionality from Related Functional Groups in Protonated Analytes by Using Selective Ion-Molecule Reactions Followed by Collision-Activated Dissociation in a Linear Quadrupole Ion Trap Mass Spectrometer.

Aziridines are commonly used as reagents for the synthesis of drug substances although they are potentially mutagenic and genotoxic. Therefore, their unambiguous detection is critically important. Unfortunately, tandem mass spectrometry (MS2) based on collision-activated dissociation (CAD), a powerful method used for the identification of many unknown compounds in complex mixtures, does not provide diagnostic fragmentation patterns for ionized aziridines. Therefore, a different mass spectrometry approach based on MS3 experiments is presented here for the identification of the aziridine functionalities. This approach is based on selective gas-phase ion-molecule reactions of protonated analytes with tris(dimethylamino)borane (TDMAB) followed by diagnostic CAD reactions in a modified linear quadrupole ion trap (LQIT) mass spectrometer. TDMAB reacts with protonated aziridines by forming adduct ions that have lost a dimethylamine (DMA) molecule ([M + H + TDMAB - HN(CH3)2]+). CAD on these product ions generated diagnostic fragment ions with m/z-values 25- and 43-units lower than those of the ion-molecule reaction product ions. None of the ion-molecule reaction product ions formed from other, structurally related, protonated analytes produced related fragment ions. Quantum chemical calculations were employed to explore the mechanisms of the observed reactions.

Development of a linear ion trap mass spectrometer capable of analyzing megadalton MALDI ions

Detecting megadalton matrix-assisted laser desorption/ionization (MALDI) ions in an ion trap mass spectrometer is a technical challenge. In this study, megadalton protein and polymer ions were successfully measured by MALDI linear ion trap mass spectrometer (LIT-MS) for the first time. The LIT-MS is comprised of a Thermo linear ion trap mass analyzer and a highly sensitive charge-sensing particle detector (CSPD). A newly designed radio frequency (rf) scan mode with dipolar resonance ejection techniques is proposed to extend the mass range of LIT-MS up to one million Thomson (Th). We analyze high mass ions with mass-to charge (m/z) ratios ranging from 100 kTh to 1 MTh, including thyroglobulin, alpha-2-macroglobulin, immunoglobulins (e.g., IgG and IgM), and polymer (∼ 940 kTh) ions. Besides, it is also very challenging for ion trap mass spectrometry to detect megadalton ions at low concentrations. By adopting high affinity carboxylated/oxidized detonation nanodiamonds (oxDNDs) to enrich IgM molecules and form antibody-nanodiamond conjugates, we have successfully reached ∼ 5 nM (5 μg/mL) concentration which is better than that by the other techniques.

SWIFTSIN: A High-Resolution Ion Isolation Waveform for the Miniaturized Linear Ion Trap Mass Spectrometer by Coarse to Fine Excitation

To figure out the reason for the drawback of the stored waveform inverse Fourier transform (SWIFT) waveform and realize the high-resolution ion isolation on the miniaturized linear ion trap mass spectrometer, we studied the efficiency that ions can be excited under different excitation durations and amplitudes at different frequencies and compared the overlap ratios of the effective excitation frequency bandwidths of the adjacent ions. According to this, we proposed a new coarse-to-fine isolation waveform named SWIFTSIN. By superposing one or more sinusoidal waveforms on the SWIFT waveform and modulating the phases of the superposed sinusoidal waveforms, the generated SWIFTSIN waveform can achieve unit mass isolation on the miniaturized linear ion trap mass spectrometer without reducing the intensity of the target ion. The isolation ability of the SWIFTSIN waveform was verified by isolating a single isotope peak in the mixed samples.

Synthesis and Characterization of Molecularly Imprinted Polymers for the Determination of Cocaine in Urine Using Microextraction in Packed Sorvent

Among stimulant drugs, cocaine deserves attention due to its high rates of seizures worldwide. This work presents the synthesis and characterization of hybrid molecularly imprinted polymers (MIPs) for use in preparing biological samples using a homemade microextraction in a packed sorbent device to extract cocaine. The MIPs synthesized using caffeine and cocaine as templates have been compared. Caffeine was used due to its low value and be easier to obtain than cocaine. Additionally, restricted access molecularly imprinted polymers (RAMIPs) were also produced for comparison purposes. The polymeric materials were characterized using scanning electron microscopy, textural analysis, Fourier transform infrared spectroscopy, and cross polarization/ magic angle spinning 13C nuclear magnetic resonance. The method optimization was performed using linear ion trap mass spectrometer to evaluate the effects of sample pH, type of eluent, washing solvent, adsorption cycles, and eluent volume. In the optimized method, RAMIPs indicated better cocaine extraction compared to MIPs. The quantitative study demonstrated that the developed method was able to accurately quantify cocaine in urine samples with values close to actual concentrations.

All Ion Fragmentation Analysis Enhances the Untargeted Profiling of Glucosinolates in Brassica Microgreens by Liquid Chromatography and High-Resolution Mass Spectrometry.

An analytical approach based on reversed-phase liquid chromatography coupled to electrospray ionization Fourier-transform mass spectrometry in negative ion mode (RPLC-ESI-(-)-FTMS) was developed for the untargeted characterization of glucosinolates (GSL) in the polar extracts of four Brassica microgreen crops, namely, garden cress, rapeseed, kale, and broccoli raab. Specifically, the all ion fragmentation (AIF) operation mode enabled by a quadrupole-Orbitrap mass spectrometer, i.e., the systematic fragmentation of all ions generated in the electrospray source, followed by the acquisition of an FTMS spectrum, was exploited. First, the best qualifying product ions for GSL were recognized from higher-energy collisional dissociation (HCD)-FTMS2 spectra of representative standard GSL. Extracted ion chromatograms (EIC) were subsequently obtained for those ions from RPLC-ESI(-)-AIF-FTMS data referred to microgreen extracts, by plotting the intensity of their signals as a function of retention time. The alignment of peaks detected in the EIC traces was finally exploited for the recognition of peaks potentially related to GSL, with the EIC obtained for the sulfate radical anion [SO4]•- (exact m/z 95.9523) providing the highest selectivity. Each putative GSL was subsequently characterized by HCD-FTMS2 analyses and by collisionally induced dissociation (CID) multistage MSn (n = 2, 3) acquisitions based on a linear ion trap mass spectrometer. As a result, up to 27 different GSLs were identified in the four Brassica microgreens. The general method described in this work appears as a promising approach for the study of GSL, known and novel, in plant extracts.

A Diagnostic Nitrosamine Detection Approach for Pharmaceuticals by Using Tandem Mass Spectrometry Based on Diagnostic Gas-Phase Ion-Molecule Reactions.

N-Nitrosamines are strictly regulated in pharmaceutical products due to their carcinogenic nature. Therefore, the ability to rapidly and reliably identify the N-nitroso functionality is urgently needed. Unfortunately, not all ionized N-nitroso compounds produce diagnostic fragment ions and hence tandem mass spectrometry based on collision-activated dissociation (CAD) cannot be used to consistently identify the N-nitroso functionality. Therefore, a more reliable method was developed based on diagnostic functional-group selective ion-molecule reactions in a linear quadrupole ion trap mass spectrometer. 2-Methoxypropene (MOP) was identified as a reagent that reacts with protonated N-nitrosamines in a diagnostic manner by forming an adduct followed by the elimination of 2-propenol (CH3C(OH)═CH2]). From 18 protonated N-nitrosamine model compounds studied, 15 formed the diagnostic product ion. The lack of the diagnostic reaction for three of the N-nitrosamine model compounds was rationalized based on the presence of a pyridine ring that gets preferentially protonated instead of the N-nitroso functionality. These N-nitrosamines can be identified by subjecting a stable adduct formed upon ion-molecule reactions with MOP to CAD. Further, the ability to use ion-molecule reactions followed by CAD to differentiate protonated O-nitroso compounds with a pyridine ring from analogous N-nitrosamines was demonstrated This methodology is considered to be robust for the identification of the N-nitroso functionality in unknown analytes. Lastly, HPLC/MS2 experiments were performed to determine the detection limit for five FDA regulated N-nitrosamines.

Proton Affinities of Alkanes.

Chemical characterization of complex mixtures of large alkanes is critically important for many fields, including petroleomics and the development of renewable transportation fuels. Tandem mass spectrometry is the only analytical method that can be used to characterize such mixtures at the molecular level. Many ionization methods used in mass spectrometry involve proton transfer to the analyte. Unfortunately, very few proton affinity (PA) values are available for alkanes. Indeed, previous research has shown that most protonated alkanes (MH+) are not stable but fragment spontaneously via the elimination of a hydrogen molecule to form [M - H]+ ions. Here, the PAs of several n-alkanes and alkylcyclohexanes containing 5-8 carbon atoms, n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane, and ethylcyclohexane, were determined via bracketing experiments by using a linear quadrupole ion trap mass spectrometer. Monitoring the formation of the [M - H]+ ions in reactions between the alkanes and protonated reference bases with known PAs revealed that the PAs of all the alkanes fell into the range 721 ± 20 kJ mol-1. In order to obtain a more accurate estimate of the relative PAs of different alkanes, two alkanes were introduced simultaneously into the ion trap and allowed to react with the same protonated reference base. Based on these experiments, the longer the alkyl chain in an n-alkane or alkylcyclohexane the greater the PA. Further, when considering alkanes with the same number of carbon atoms, the PAs of those with a cyclohexane ring were found to be greater than those with no such ring.

A Portable Reagent Inlet System Designed to Diminish the Impact of Air and Water to Ion-Molecule Reactions Studied in a Linear Quadrupole Ion Trap.

A portable reagent inlet system for a linear quadrupole ion trap (LQIT) mass spectrometer was designed to diminish the impact of air and water on gas-phase ion-molecule reactions. Compared to the traditional reagent mixing manifolds that has been extensively used for decades, the portable system is much simpler and has fewer junctions and a smaller inner space. These changes reduce the amount of air and water introduced into the mass spectrometer with the reagent. Furthermore, unlike the traditional manifolds, the portable system can be easily attached to or detached from the LQIT mass spectrometer. Finally, the price of the portable system is only 1/10 of that of a traditional manifold as estimated in 2022. Therefore, the portable system has several advantages over the traditional reagent mixing manifolds.

Tandem Mass Spectrometric Characterization of the Molecular Radical Cations of Asphaltenes

Asphaltenes, the heaviest fraction of crude oil, are problematic for the oil industry for several reasons. For example, they have a tendency to precipitate out of oil pipelines, thus causing clogs. Further, they can foul catalysts used in refining of crude oil. However, the lack of knowledge on the exact molecular structures of asphaltenes has long prevented addressing the above problems and also hindered finding financially beneficial uses for asphaltenes. This paper focuses on recent advances on the structural characterization of the molecular radical cations of asphaltenes based on collision-activated dissociation (CAD) experiments performed using linear quadrupole ion trap mass spectrometers coupled to an Orbitrap detector. Stable molecular radical cations are readily generated from asphaltenes upon atmospheric pressure chemical ionization (APCI) when using CS2 as the solvent because this solvent cannot transfer a proton to analytes. MS2–MS5 experiments based on ion-source CAD (ISCAD), ion-trap CAD (ITCAD), and/or medium-energy CAD (MCAD) were explored for the structural characterization of these molecular radical cations by using model compounds. Energy-resolved MCAD experiments were identified as the most useful experiments because they provide substantially more structural information for the radical cations than the other CAD experiments mentioned above. In some MSn experiments, MSn–1 was first performed in the ion trap, followed by isolation of a desired ion in the ion trap and transfer into the MCAD collision cell, wherein it was subjected to energy-resolved MCAD followed by high-resolution detection of the fragment ions. The various CAD experiments were used to obtain information on compounds in asphaltene samples with different origins, such as the aliphatic carbon content, molecular weight distributions (MWDs), average molecular weight, number of aromatic carbon atoms, number of aromatic rings in the core, and relative abundances of single-core and multicore compounds.

Electrospray ionization in-source decay of N-glycans and the effects on N-glycan structural identification.

Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are soft ionization techniques commonly used in mass spectrometry. Although in-source and post-source decays of MALDI have been investigated extensively, the analogous decays of ESI have received little attention. Previous studies regarding the analogous decays of ESI focus on the dissociation of multiply charged proteins and peptides. The decay of carbohydrates in ESI has not been investigated yet, and it may have interference in carbohydrate structural determination. Commercial apparatus, including a high-performance liquid chromatography (HPLC), an ESI source, and a linear ion trap mass spectrometer, were used to investigate the fragmentation of several N-glycans during the ESI process. About 0.2%-3% of neutral N-glycans and more than 50% of N-glycans consisting of a sialic acid are dissociated into small N-glycans by ESI in-source decay in typical ESI operating conditions. The efficiencies of most dissociation channels increase as the temperature of ion transfer capillary increases, indicating that part of the energy deposited into the precursor ions for cracking is from the heated capillary. The cracking patterns of ESI in-source decay are slightly different from those of gaseous phase collision-induced dissociation. Large N-glycans are dissociated into small N-glycans in ESI in-source decay that may result in the interference of the structural identification of small N-glycans. Separation of large N-glycans from small N-glycans, for example, using HPLC, prior to ESI ionization is necessary to eliminate the interference. This is particularly important when N-glycans consist of sialic acid or large N-glycans have much higher concentration than that of small N-glycans in ESI solution.

Detection of Trace Explosives Using a Novel Sample Introduction and Ionization Method.

A novel sample introduction and ionization method for trace explosives detection is proposed and investigated herein, taking into consideration real-world application requirements. A thermal desorption sampling method and dielectric barrier discharge ionization (DBDI) source, with air as the discharge gas, were developed. The counter flow method was adopted firstly into the DBDI source to remove the interference of ozone and other reactive nitrogen oxides. A separated reaction region with an ion guiding electric field was developed for ionization of the sample molecules. Coupled with a homemade miniature digital linear ion trap mass spectrometer, this compact and robust design, with further optimization, has the advantages of soft ionization, a low detection limit, is free of reagent and consumable gas, and is an easy sample introduction. A range of common nitro-based explosives including TNT, 2,4-DNT, NG, RDX, PETN, and HMX has been studied. A linear response in the range of two orders of magnitude with a limit of detection (LOD) of 0.01 ng for TNT has been demonstrated. Application to the detection of real explosives and simulated mixed samples has also been explored. The work paves the path to developing next generation mass spectrometry (MS) based explosive trace detectors (ETDs).

Development and validation of an LC-MS/MS method for determination of B vitamins and some its derivatives in whole blood.

Obligate symbiotic bacteria associated with the insects feeding exclusively on vertebrate blood are supposed to complement B vitamins presumably lacking in their diet. Recent genomic analyses revealed considerable differences in biosynthetic capacities across different symbionts, suggesting that levels of B vitamins may vary across different vertebrate hosts. However, a rigorous determination of B vitamins content in blood of various vertebrates has not yet been approached. A reliable analytical method focused on B vitamin complex in blood can provide valuable informative background and understanding of general principles of insect symbiosis. In this work, a chromatographic separation of eight B vitamins (thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folic acid, and cyanocobalamine), four B vitamin derivatives (niacinamide, pyridoxal-5-phosphate, 4-pyridoxic acid, and tetrahydrofolic acid), and 3 stable isotope labelled internal standards was developed. Detection was carried out using dual-pressure linear ion trap mass spectrometer in FullScan MS/MS and SIM mode. Except for vitamin B9 (tetrahydrofolic acid), the instrument quantitation limits of all analytes were ranging from 0.42 to 5.0 μg/L, correlation coefficients from 0.9997 to 1.0000, and QC coefficients from 0.53 to 3.2%. Optimization of whole blood sample preparation step was focused especially on evaluation of two types of protein-precipitation agents: trichloroacetic acid and zinc sulphate in methanol. The best results were obtained for zinc sulphate in methanol, but only nine analytes were successfully validated. Accuracy of the procedure using this protein-precipitating agent was ranging from 89 to 120%, precision from 0.5 to 13%, and process efficiency from 65 to 108%. The content of B vitamins in whole blood samples from human and various vertebrates is presented as an application example of this newly developed method.

Development and validation of a high-performance liquid chromatography tandem mass spectrometry method for the quantification of the antiparasitic and antifungal drug amphotericin B in human skin tissue

Amphotericin B is an antifungal and antiparasitic drug used in first-line treatment of the parasitic neglected tropical disease leishmaniasis. Liposomal amphotericin B is currently studied for the treatment of cutaneous and post-kala-azar dermal leishmaniasis, where the dermis of the skin is infected with Leishmania parasites. For the optimization of known treatment regimens, accurate target-site concentrations of the drug are required. To date, no assay was available to assess human skin concentrations of amphotericin B. We here present a bioanalytical assay for the quantification of amphotericin B in 4-mm human skin biopsies. Human skin biopsies were homogenized by overnight digestion using collagenase A and were processed afterwards by simple protein precipitation using methanol. Separation and detection were achieved using a Gemini C18 column with slightly acidic chromatographic conditions and a quadrupole – linear ion trap mass spectrometer, respectively. The method was validated in digestion solution over a range of 10–2,000 ng/mL using natamycin as internal standard, with a correlation coefficient (r2) of at least 0.9974. The assay performance, accuracy and precision, were acceptable over the validated range, using international (EMA and FDA) acceptance criteria. In the skin tissue extracts, amphotericin B ion enhancement was observed, however, the internal standard (IS) corrected for this effect hence calibration standards in digestion solvent could be used as a surrogate matrix for the quantification in skin tissue. Sample preparation recoveries were low (around 27%) because of degradation of amphotericin B during digestion and sample preparation processes, albeit highly reproducible, without compromising the accuracy and precision of the method. Using this assay, amphotericin B could be detected and quantified in skin biopsies originating from treated Indian post-kala-azar dermal leishmaniasis patients.