Manipulation of Gaseous Ions with Acoustic Fields at Atmospheric Pressure.

The ability to controllably move gaseous ions is an essential aspect of ion-based spectrometry (e.g., mass spectrometry and ion mobility spectrometry) as well as materials processing. At higher pressures, ion motion is largely governed by diffusion and multiple collisions with neutral gas molecules. Thus, high-pressure ion optics based on electrostatics require large fields, radio frequency drives, complicated geometries, and/or partially transmissive grids that become contaminated. Here, we demonstrate that low-power standing acoustic waves can be used to guide, block, focus, and separate beams of ions akin to electrostatic ion optics. Ions preferentially travel through the static-pressure regions ("nodes") while neutral gas does not appear to be impacted by the acoustic field structure and continues along a straight trajectory. This acoustic ion manipulation (AIM) approach has broad implications for ion manipulation techniques at high pressure, while expanding our fundamental understanding of the behavior of ions in gases.

Miniaturized Protein Digestion Using Acoustic Levitation with Online High Resolution Mass Spectrometry.

The combination of acoustically levitated droplets, mid-IR laser evaporation, and subsequent post-ionization by secondary electrospray ionization was applied for monitoring the enzymatic digestion of various proteins. Acoustically levitated droplets are an ideal, wall-free model reactor, readily allowing compartmentalized microfluidic trypsin digestions. Time-resolved interrogation of the droplets yielded real-time information on the progress of the reaction and thus provided insights into reaction kinetics. After 30 min of digestion in the acoustic levitator, the obtained protein sequence coverages were identical to the reference overnight digestions. Importantly, our results clearly demonstrate that the applied experimental setup can be used for the real-time investigation of chemical reactions. Furthermore, the described methodology only uses a fraction of the typically applied amounts of solvent, analyte, and trypsin. Thus, the results exemplify the use of acoustic levitation as a green analytical chemistry alternative to the currently used batch reactions.

Industry Perspective on Therapeutic Peptide Drug-Drug Interaction Assessments During Drug Development: A European Federation of Pharmaceutical Industries and Associations White Paper.

Drug-drug interaction (DDI) assessments are well defined in health authority guidelines for small molecule drugs, and US Food and Drug Administration (FDA) draft guidance is now available for therapeutic proteins. However, there are currently no regulatory guidelines outlining DDI assessments for therapeutic peptides, which poses significant uncertainty and challenges during drug development for this heterogenous class of molecules. A cross-industry peptide DDI working group consisting of experts from 10 leading companies was formed under the sponsorship of the European Federation of Pharmaceutical Industries and Associations. We aimed to capture the range of DDI studies undertaken for peptide drugs by (i) anonymously surveying relevant companies involved in peptide drug development to better understand DDI study type/timing currently performed and (ii) compiling a database containing in vitro / clinical DDI data from submission packages for recently approved peptide drugs. Our analyses highlight significant gaps and uncertainty in the field. For example, the reported timing of in vitro peptide DDI studies, if performed, vary substantially across responding companies from early research to phase III. Nearly all in vitro cytochrome P450 / transporter inhibition studies reported in the survey were negative. For the few positive hits reported, no clinical follow-up studies were performed, questioning the clinical relevance of these findings. Furthermore, available submission packages reveal DDI likelihood is low for peptides >2 kDa, making it reasonable to adopt a risk-based approach during drug development for larger peptides. By benchmarking the landscape of peptide DDI activities across the industry, we set the stage for future discussions with health authorities on harmonizing peptide DDI approaches.

Pediatric trauma and emergency surgery: an international cross-sectional survey among WSES members.

BACKGROUND: In contrast to adults, the situation for pediatric trauma care from an international point of view and the global management of severely injured children remain rather unclear. The current study investigates structural management of pediatric trauma in centers of different trauma levels as well as experiences with pediatric trauma management around the world. METHODS: A web-survey had been distributed to the global mailing list of the World Society of Emergency Surgery from 10/2021-03/2022, investigating characteristics of respondents and affiliated hospitals, case-load of pediatric trauma patients, capacities and infrastructure for critical care in children, trauma team composition, clinical work-up and individual experiences with pediatric trauma management in response to patients´ age. The collaboration group was subdivided regarding sizes of affiliated hospitals to allow comparisons concerning hospital volumes. Comparable results were conducted to statistical analysis. RESULTS: A total of 133 participants from 34 countries, i.e. 5 continents responded to the survey. They were most commonly affiliated with larger hospitals (> 500 beds in 72.9%) and with level I or II trauma centers (82.0%), respectively. 74.4% of hospitals offer unrestricted pediatric medical care, but only 63.2% and 42.9% of the participants had sufficient experiences with trauma care in children ≤ 10 and ≤ 5 years of age (p = 0.0014). This situation is aggravated in participants from smaller hospitals (p < 0.01). With regard to hospital size (≤ 500 versus > 500 in-hospital beds), larger hospitals were more likely affiliated with advanced trauma centers, more elaborated pediatric intensive care infrastructure (p < 0.0001), treated children at all ages more frequently (p = 0.0938) and have higher case-loads of severely injured children < 12 years of age (p = 0.0009). Therefore, the majority of larger hospitals reserve either pediatric surgery departments or board-certified pediatric surgeons (p < 0.0001) and in-hospital trauma management is conducted more multi-disciplinarily. However, the majority of respondents does not feel prepared for treatment of severe pediatric trauma and call for special educational and practical training courses (overall: 80.2% and 64.3%, respectively). CONCLUSIONS: Multi-professional management of pediatric trauma and individual experiences with severely injured children depend on volumes, level of trauma centers and infrastructure of the hospital. However, respondents from hospitals at all levels of trauma care complain about an alarming lack of knowledge on pediatric trauma management.

Laser Ablation Secondary Electrospray Ionization for In Situ Mass Spectrometric Interrogation of Acoustically-Levitated Droplets.

The composition of acoustically levitated droplets was probed by a novel combination of mid-IR laser evaporation and subsequent postionization via secondary electrospray ionization. The combination of microliter samples and subnanoliter sampling provided time-resolved interrogation of droplets and allowed for a kinetic investigation of the laser-induced release of the analyte, which was found to strongly depend on the analytes. The observed substance-specific delayed release of the analytes permitted baseline-separated discrimination of the analytes, ideal for the study of complex samples. The additionally applied postionization scheme was found to enable efficient detection of small volatile compounds as well as peptides. The detection of small molecules and peptides occurred under very different sampling geometries, pointing to two distinct underlying ionization mechanisms. Overall, our results suggest that the experimental setup presented in this study can serve as a widely applicable platform to study chemical reactions in acoustically levitated droplets as model reactors.

Preclinical pharmacology of RA15127343: In vitro and in vivo activity of a novel ultralong-acting basal insulin.

AIM: To report the in vitro and in vivo preclinical pharmacokinetic (PK) and pharmacodynamic (PD) properties of RA15127343, a novel ultralong-acting insulin analogue targeting once-weekly administration, in female Göttingen minipigs. METHODS: In vitro binding and activation of human insulin receptor isoforms (IR-A/IR-B), glucose uptake in rat myocytes, as well as mitogenic activity of RA15127343 were evaluated. In vivo, the PK and PD activities of RA15127343 were assessed in female, normoglycaemic Göttingen minipigs. The half-life (t1/2 ) and time to maximum plasma concentration (Tmax ) of subcutaneously (SC) administered RA15127343 (10/30/45/60 nmol/kg) were estimated. In vivo blood glucose and endogenous plasma C-peptide concentrations after single SC administration (10/30/45/60 nmol/kg) or repeated dosing (15 nmol/kg) were analysed. RESULTS: In comparison to human insulin, RA15127343 showed lower in vitro binding affinity (19.9/6.31 µM vs. 1.10/1.14 nM) and activation (2.054 µM/669.6 nM vs. 26.04/18.24 nM) of IR-A/IR-B, lower potency to activate glucose uptake (855.2 vs. 3.37 nM) and lower mitogenic activity (17.92 µM vs. 10.78 nM; proliferation in MCF7 cells). In vivo, the mean t1/2 and Tmax of RA15127343 after SC administration ranged from 48 to 59 and 30 to 39 hours, respectively. Blood glucose and plasma C-peptide concentrations were significantly lower with RA15127343 (single/repeated doses) versus vehicle. CONCLUSIONS: RA15127343 showed an ultra-long t1/2 with a slow onset of action. The preclinical pharmacological outcomes suggest RA15127343 could be a potential ultralong-acting insulin analogue with low risk of hypoglycaemia in humans.

Determination of lithium in human serum by isotope dilution atomic absorption spectrometry.

The therapeutic dose of lithium (Li) compounds, which are widely used for the treatment of psychiatric and hematologic disorders, is close to its toxic level; therefore, drug monitoring protocols are mandatory. Herein, we propose a fast, simple, and low-cost analytical procedure for the traceable determination of Li concentration in human serum, based on the monitoring of the Li isotope dilution through the partially resolved isotope shift in its electronic transition around 670.80 nm using a commercially available high-resolution continuum source graphite furnace atomic absorption spectrometer. With this technique, serum samples only require acidic digestion before analysis. The procedure requires three measurements-an enriched 6Li spike, a mixture of a certified standard solution and spike, and a mixture of the sample and spike with a nominal 7Li/6Li ratio of 0.82. Lanthanum has been used as an internal spectral standard for wavelength correction. The spectra are described as the linear superposition of the contributions of the respective isotopes, each consisting of a spin-orbit doublet, which can be expressed as Gaussian components with constant spectral position and width and different relative intensity, reflecting the isotope ratio in the sample. Both the spectral constants and the correlation between isotope ratio and relative band intensity have been experimentally obtained using commercially available materials enriched with Li isotopes. The Li characteristic mass (mc) obtained corresponds to 0.6 pg. The procedure has been validated using five human serum certified reference materials. The results are metrologically comparable and compatible to the certified values. The measurement uncertainties are comparable to those obtained by the more complex and expensive technique, isotope dilution mass spectrometry.

An Effective QWBA/UHPLC-MS/Tissue Punch Approach: Solving a Pharmacokinetic Issue via Quantitative Met-ID.

BACKGROUND: Methods to provide absolute quantitation of the administered drug and corresponding metabolites in tissue in a spatially resolved manner is a challenging but much needed capability in pharmaceutical research. Quantitative Whole-Body Autoradiography (QWBA) after a single- dose intravenous (3 mg/kg) and extravascular (30 mg/kg) administrations of an in vitro metabolically stable test compound (structure not reported here) indicated quick tissue distribution and excretion. OBJECTIVE: Good bioavailability and short in vivo half-lives were determined formerly for the same test compound. For closing gaps in the understanding of pharmacokinetic data and in vitro results, radioactive hot spots on whole-body tissue sections had been profiled. METHODS: Punches from selected tissue regions containing high radioactivity in the tissue sections previously analyzed by QWBA were extracted by a highly organic solvent and analyzed without any consecutive sample preparation step, applying Ultra High Performance Liquid Chromatography- Mass Spectrometry (UHPLC-MS) and off-line radioanalysis to maximize signal levels for metabolite identification and profiling. RESULTS: The analysis revealed that the test compound was metabolized intensively by phase I reactions in vivo and the metabolites formed were excreted in bile and urine. The predominant metabolites showed abundant signal intensities both by MS and by radioanalysis but the MS signal intensities generally underestimated the real abundances of metabolites relative to the unchanged drug. CONCLUSION: This work illustrates that maximizing the sensitivity of tissue punch radioanalysis and the combination with UHPLC-MS leads to a better insight into pharmacokinetic processes by providing quantitative data with high molecular selectivity.

Approaching phase-imaging through defocusing shadowgraphy for acoustic resonator diagnosis and the capability of direct index-of-refraction measurements.

The visualization of index-of-refraction (IoR) distribution is one of the common methods to investigate fluid flow or pressure fields. While schlieren and shadowgraphy imaging techniques are widely accepted, their inherent limitations often lead to difficulties in elucidating the IoR distribution and extracting the true IoR information from the resulting images. While sophisticated solutions exist, the IoR-gradient-to-image was achieved by purposely introducing a commonly avoided "defect" into the optical path of a conventional coincident schlieren/shadowgraphy setup; the defect is a combination of slight defocusing and the use of non-conjugate optical components. As such, the method presented in this work is referred to as defocusing shadowgraphy, or DF-shadowgraphy. While retaining the ease of a conventional schlieren/shadowgraphy geometry, this DF approach allows direct visualization of complicated resonant acoustic fields even without any data processing. For instance, the transient acoustic fields of a common linear acoustic resonator and a two-dimensional one were directly visualized without inversion. Moreover, the optical process involved in DF-shadowgraphy was investigated from a theoretical perspective. A numerical solution of the sophisticated impulse response function was obtained, which converts the phase distortion into intensity distributions. Based on this solution, the IoRs of various gas streams (e.g., CO2 and isopropanol vapor) were determined from single images.

Ageing Effects in Mounting Media of Microscope Slide Samples from Natural History Collections: A Case Study with Canada Balsam and PermountTM.

Microscope slide collections represent extremely valuable depositories of research material in a natural history, forensic, veterinary, and medical context. Unfortunately, most mounting media of these slides deteriorate over time, with the reason for this not yet understood at all. In this study, Raman spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and different types of light microscopy were used to investigate the ageing behaviour of naturally aged slides from museum collections and the experimentally aged media of Canada balsam and Permount™, representing a natural and a synthetic resin, respectively, with both being based on mixtures of various terpenes. Whereas Canada balsam clearly revealed chemical ageing processes, visible as increasing colouration, Permount™ showed physical deterioration recognisable by the increasing number of cracks, which even often impacted a mounted specimen. Noticeable changes to the chemical and physical properties of these mounting media take decades in the case of Canada balsam but just a few years in the case of Permount™. Our results question whether or not Canada balsam should really be regarded as a mounting medium that lasts for centuries, if its increasing degree of polymerisation can lead to a mount which is no longer restorable.

High-Resolution Atomic Absorption Spectrometry Combined With Machine Learning Data Processing for Isotope Amount Ratio Analysis of Lithium.

An alternative method for lithium isotope amount ratio analysis based on a combination of high-resolution atomic absorption spectrometry and spectral data analysis by machine learning (ML) is proposed herein. It is based on the well-known isotope shift of approximately 15 pm for the electronic transition 22P←22S at around the wavelength of 670.8 nm, which can be measured by the state-of-the-art high-resolution continuum source graphite furnace atomic absorption spectrometry. For isotope amount ratio analysis, a scalable tree boosting ML algorithm (XGBoost) was employed and calibrated using a set of samples with 6Li isotope amount fractions, ranging from 0.06 to 0.99 mol mol-1, previously determined by a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). The calibration ML model was validated with two certified reference materials (LSVEC and IRMM-016). The procedure was applied toward the isotope amount ratio determination of a set of stock chemicals (Li2CO3, LiNO3, LiCl, and LiOH) and a BAM candidate reference material NMC111 (LiNi1/3Mn1/3Co1/3O2), a Li-battery cathode material. The results of these determinations were compared with those obtained by MC-ICP-MS and found to be metrologically comparable and compatible. The residual bias was -1.8‰, and the precision obtained ranged from 1.9 to 6.2‰. This precision was sufficient to resolve naturally occurring variations, as demonstrated for samples ranging from approximately -3 to +15‰. To assess its suitability to technical applications, the NMC111 cathode candidate reference material was analyzed using high-resolution continuum source atomic absorption spectrometry with and without matrix purification. The results obtained were metrologically compatible with each other.

Quantitative Analysis of Pharmaceutical Drugs Using a Combination of Acoustic Levitation and High Resolution Mass Spectrometry.

A combination of acoustic levitation, laser vaporization, and atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is presented in this study that enabled sensitive analysis of pharmaceutical drugs from an aqueous sample matrix. An unfocused pulsed infrared laser provided contactless sample desorption from the droplets trapped inside an acoustic levitator by activation of the OH stretching band of aqueous and alcoholic solvents. Subsequent atmospheric pressure chemical ionization was used between the levitated droplet and the mass spectrometer for postionization. In this setup, the unfocused laser gently desorbed the analytes by applying very mild repulsive forces. Detailed plume formation studies by temporally resolved schlieren experiments were used to characterize the liquid gas transition in this process. In addition, the role of different additives and solvent composition was examined during the ionization process. The analytical application of the technique and the proof-of-concept for quantitative analysis were demonstrated by the determination of selected pharmaceutical drugs in aqueous matrix with limits of quantification at the lower nanomolar level and a linear dynamic range of 3-4 orders of magnitude.

Unsupervised Reconstruction of Analyte-Specific Mass Spectra Based on Time-Domain Morphology with a Modified Cross-Correlation Approach.

Concomitant species that appear at the same or very similar times in a mass-spectral analysis can clutter a spectrum because of the coexistence of many analyte-related ions (e.g., molecular ions, adducts, fragments). One method to extract ions stemming from the same origin is to exploit the chemical information encoded in the time domain, where the individual temporal appearances inside the complex structures of chronograms or chromatograms differ with respect to analytes. By grouping ions with very similar or identical time-domain structures, single-component mass spectra can be reconstructed, which are much easier to interpret and are library-searchable. While many other approaches address similar objectives through the Pearson's correlation coefficient, we explore an alternative method based on a modified cross-correlation algorithm to compute a metric that describes the degree of similarity between features inside any two ion chronograms. Furthermore, an automatic workflow was devised to be capable of categorizing thousands of mass-spectral peaks into different groups within a few seconds. This approach was tested with direct mass-spectrometric analyses as well as with a simple, fast, and poorly resolved LC-MS analysis. Single-component mass spectra were extracted in both cases and were identified based on accurate mass and a mass-spectral library search.

Stimulated Raman scattering by intracavity mixing of nanosecond laser excitation and fluorescence in acoustically levitated droplets.

Raman spectroscopy is becoming a commonly used, powerful tool for structural elucidation and species identification of small liquid samples, e.g. in droplet-based digital microfluidic devices. Due to the low scattering cross sections and the temporal restrictions dictated by the droplet flow, however, it depends on amplification strategies which often come at a cost. In the case of surface-enhanced Raman scattering (SERS), this can be an enhanced susceptibility towards memory effects and cross talk, whereas resonant and/or stimulated Raman techniques require higher instrumental sophistication, such as tunable lasers or the high electromagnetic field strengths which are typically provided by femtosecond lasers. Here, an alternative instrumental approach is discussed, in which stimulated Raman scattering (SRS) is achieved using the single fixed wavelength output of an inexpensive diode-pumped solid-state (DPSS) nanosecond laser. The required field strengths are realized by an effective light trapping in a resonator mode inside the interrogated droplets, while the resonant light required for the stimulation is provided by the fluorescence signal of an admixed laser dye. To elucidate the underlying optical processes, proof-of-concept experiments are conducted on acoustically levitated droplets, mimicking a highly reproducible and stable digital fluidic system. By using isotope-labeled compounds, the assignment of the emitted radiation as Raman scattering is firmly corroborated. A direct comparison reveals an amplification of the usually weak spontaneous Stokes emission by up to five orders of magnitude. Further investigation of the optical power dependence reveals the resulting gain to depend on the intensity of both, the input laser fluence and the concentration of the admixed fluorophore, leaving SRS as the only feasible amplification mechanism. While in this study stable large droplets have been studied, the underlying principles also hold true for smaller droplets, in which case significantly lower laser pulse energy is required. Since DPSS lasers are readily available with high repetition rates, the presented detection strategy bears a huge potential for fast online identification and characterization routines in digital microfluidic devices.

Design, Synthesis, and Pharmacological Evaluation of Potent Positive Allosteric Modulators of the Glucagon-like Peptide-1 Receptor (GLP-1R).

The therapeutic success of peptidic GLP-1 receptor agonists for treatment of type 2 diabetes mellitus (T2DM) motivated our search for orally bioavailable small molecules that can activate the GLP-1 receptor (GLP-1R) as a well-validated target for T2DM. Here, the discovery and characterization of a potent and selective positive allosteric modulator (PAM) for GLP-1R based on a 3,4,5,6-tetrahydro-1H-1,5-epiminoazocino[4,5-b]indole scaffold is reported. Optimization of this series from HTS was supported by a GLP-1R ligand binding model. Biological in vitro testing revealed favorable ADME and pharmacological profiles for the best compound 19. Characterization by in vivo pharmacokinetic and pharmacological studies demonstrated that 19 activates GLP-1R as positive allosteric modulator (PAM) in the presence of the much less active endogenous degradation product GLP1(9-36)NH2 of the potent endogenous ligand GLP-1(7-36)NH2. While these data suggest the potential of small molecule GLP-1R PAMs for T2DM treatment, further optimization is still required towards a clinical candidate.

Laser ionization ion mobility spectrometric interrogation of acoustically levitated droplets.

Acoustically levitated droplets have been suggested as compartmentalized, yet wall-less microreactors for high-throughput reaction optimization purposes. The absence of walls is envisioned to simplify up-scaling of the optimized reaction conditions found in the microliter volumes. A consequent pursuance of high-throughput chemistry calls for a fast, robust and sensitive analysis suited for online interrogation. For reaction optimization, targeted analysis with relatively low sensitivity suffices, while a fast, robust and automated sampling is paramount. To follow this approach, in this contribution, a direct coupling of levitated droplets to a homebuilt ion mobility spectrometer (IMS) is presented. The sampling, transfer to the gas phase, as well as the ionization are all performed by a single exposure of the sampling volume to the resonant output of a mid-IR laser. Once formed, the nascent spatially and temporally evolving analyte ion cloud needs to be guided out of the acoustically confined trap into the inlet of the ion mobility spectrometer. Since the IMS is operated at ambient pressure, no fluid dynamic along a pressure gradient can be employed. Instead, the transfer is achieved by the electrostatic potential gradient inside a dual ring electrode ion optics, guiding the analyte ion cloud into the first stage of the IMS linear drift tube accelerator. The design of the appropriate atmospheric pressure ion optics is based on the original vacuum ion optics design of Wiley and McLaren. The obtained experimental results nicely coincide with ion trajectory calculations based on a collisional model. Graphical Abstract.

VUV Photodissociation Induced by a Deuterium Lamp in an Ion Trap.

Tandem mass spectrometry represents an important analytical tool to unravel molecular structures and to study the gas-phase behavior of organic molecules. Besides commonly used methods like collision-induced dissociation and electron capture or transfer dissociation, new ultraviolet light-based techniques have the potential to synergistically add to the activation methods. Here, we present a new simple, yet robust, experimental design for polychromatic activation of trapped ions using the 115-160 nm output of a commercially available deuterium lamp. The resulting continuous dissociative excitation with photons of a wide energy range from 7.7 to 10.8 eV is studied for a comprehensive set of analyte classes in both positive and negative ion modes. While being simple, affordable, compact, and of low maintenance, the new setup initiates fragmentation of most precursor ions via their known dissociation pathways. Additionally, some new fragmentation patterns were discovered. Especially, electron loss and electron capture reactions with subsequent fragmentations were observed. For oligonucleotides, peptides, carbohydrates, and organic dyes, in comparison to collision-induced dissociation, a significantly wider fragment distribution was obtained, resulting in an information increase. Since the individual photons carry enough energy to post-ionize the nascent fragments, a permanent vacuum ultraviolet light exposure inside the ion trap potentially goes along with a general increase in detection capability.

Mechanistic investigations of the liver toxicity of the free fatty acid receptor 1 agonist fasiglifam (TAK875) and its primary metabolites.

For fasiglifam (TAK875) and its metabolites the substance-specific mechanisms of liver toxicity were studied. Metabolism studies were run to identify a putatively reactive acyl glucuronide metabolite. In vitro cytotoxicity and caspase 3/7 activation were assessed in primary human and dog hepatocytes in 2D and 3D cell culture. Involvement of glutathione (GSH) detoxication system in mediating cytotoxicity was determined by assessing potentiation of cytotoxicity in a GSH depleted in vitro system. In addition, potential mitochondrial liabilities of the compounds were assessed in a whole-cell mitochondrial functional assay. Fasiglifam showed moderate cytotoxicity in human primary hepatocytes in the classical 2D cytotoxicity assays and also in the complex 3D human liver microtissue (hLiMT) after short-term treatment (24 hours or 48 hours) with TC50 values of 56 to 68 µM (adenosine triphosphate endpoint). The long-term treatment for 14 days in the hLiMT resulted in a slight TC50 shift over time of 2.7/3.6 fold lower vs 24-hour treatment indicating possibly a higher risk for cytotoxicity during long-term treatment. Cellular GSH depletion and impairment of mitochondrial function by TAK875 and its metabolites evaluated by Seahorse assay could not be found being involved in DILI reported for TAK875. The acyl glucuronide metabolites of TAK875 have been finally identified to be the dominant reason for liver toxicity.

Laser-Induced Microplasma as an Ambient Ionization Approach for the Mass-Spectrometric Analysis of Liquid Samples.

An airborne high repetition rate laser-induced plasma was applied as a versatile ambient ionization source for mass-spectrometric determinations of polar and nonpolar analytes in solution. The laser plasma was sustained between a home-built pneumatic nebulizer and the inlet capillary of an Orbitrap mass spectrometer. To maintain stable conditions in the droplet-rich spray environment, the plasma was directly fed by the fundamental output (λ = 1064 nm) of a current state-of-the-art diode-pumped solid-state laser. Ionization by the laser-driven plasma resulted in signals of intact analyte ions of several chemical categories. The analyte ions were found to be fully desolvated since no further increase in ion signal was observed upon heating of the inlet capillary. Due to the electroneutrality of the plasma, both positive and negative analyte ions could be formed simultaneously without altering the operational parameters of the ion source. While, typically, polar analytes with pronounced gas phase basicities worked best, nonpolar and amphoteric compounds were also detected. The latter were detected with lower ion signals and were prone to a certain degree of fragmentation induced during the ionization process. All the described attests the laser-induced microplasma by a good performance in terms of stability, robustness, sensitivity, and general applicability as a self-contained ion source for the liquid sample introduction.

Comparison of the fragmentation behavior of DNA and LNA single strands and duplexes.

DNA and locked nucleic acid (LNA) were characterized as single strands, as well as double stranded DNA-DNA duplexes and DNA-LNA hybrids using tandem mass spectrometry with collision-induced dissociation. Additionally, ion mobility spectrometry was carried out on selected species. Oligonucleotide duplexes of different sequences-bearing mismatch positions and abasic sites of complementary DNA 15-mers-were investigated to unravel general trends in their stability in the gas phase. Single-stranded LNA oligonucleotides were also investigated with respect to their gas phase behavior and fragmentation upon collision-induced dissociation. In contrast to the collision-induced dissociation of DNA, almost no base loss was observed for LNAs. Here, backbone cleavages were the dominant dissociation pathways. This finding was further underlined by the need for higher activation energies. Base losses from the LNA strand were also absent in fragmentation experiments of the investigated DNA-LNA hybrid duplexes. While DNA-DNA duplexes dissociated easily into single stranded fragments, the high stability of DNA-LNA hybrids resulted in predominant fragmentation of the DNA part rather than the LNA, while base losses were only observed from the DNA single strand of the hybrid.