Medical Swab Analysis Using Desorption Electrospray Ionization Mass Spectrometry: A Noninvasive Approach for Mucosal Diagnostics

Revolutionizing food science with mass spectrometry imaging: A comprehensive review of applications and challenges

Food science encounters increasing complexity and challenges, necessitating more efficient, accurate, and sensitive analytical techniques. Mass spectrometry imaging (MSI) emerges as a revolutionary tool, offering more molecular-level insights. This review delves into MSI's applications and challenges in food science. It introduces MSI principles and instruments such as matrix-assisted laser desorption/ionization, desorption electrospray ionization, secondary ion mass spectrometry, and laser ablation inductively coupled plasma mass spectrometry, highlighting their application in chemical composition analysis, variety identification, authenticity assessment, endogenous substance, exogenous contaminant and residue analysis, quality control, and process monitoring in food processing and food storage. Despite its potential, MSI faces hurdles such as the complexity and cost of instrumentation, complexity in sample preparation, limited analytical capabilities, and lack of standardization of MSI for food samples. While MSI has a wide range of applications in food analysis and can provide more comprehensive and accurate analytical results, challenges persist, demanding further research and solutions. The future development directions include miniaturization of imaging devices, high-resolution and high-speed MSI, multiomics and multimodal data fusion, as well as the application of data analysis and artificial intelligence. These findings and conclusions provide valuable references and insights for the field of food science and offer theoretical and methodological support for further research and practice in food science.

Molecular characterization of human peripheral nerves using desorption electrospray ionization mass spectrometry imaging

Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) is a molecular imaging method that can be used to elucidate the small-molecule composition of tissues and map their spatial information using two-dimensional ion images. This technique has been used to investigate the molecular profiles of variety of tissues, including within the central nervous system, specifically the brain and spinal cord. To our knowledge, this technique has yet to be applied to tissues of the peripheral nervous system (PNS). Data generated from such analyses are expected to advance the characterization of these structures. The study aimed to: (i) establish whether DESI-MSI can discriminate the molecular characteristics of peripheral nerves and distinguish them from surrounding tissues and (ii) assess whether different peripheral nerve subtypes are characterized by unique molecular profiles. Four different nerves for which are known to carry various nerve fiber types were harvested from a fresh cadaveric donor: mixed, motor and sensory (sciatic and femoral); cutaneous, sensory (sural); and autonomic (vagus). Tissue samples were harvested to include the nerve bundles in addition to surrounding connective tissue. Samples were flash-frozen, embedded in optimal cutting temperature compound in cross-section, and sectioned at 14 μm. Following DESI-MSI analysis, identical tissue sections were stained with hematoxylin and eosin. In this proof-of-concept study, a combination of multivariate and univariate statistical methods was used to evaluate molecular differences between the nerve and adjacent tissue and between nerve subtypes. The acquired mass spectral profiles of the peripheral nerve samples presented trends in ion abundances that seemed to be characteristic of nerve tissue and spatially corresponded to the associated histology of the tissue sections. Principal component analysis (PCA) supported the separation of the samples into distinct nerve and adjacent tissue classes. This classification was further supported by the K-means clustering analysis, which showed separation of the nerve and background ions. Differences in ion expression were confirmed using ANOVA which identified statistically significant differences in ion expression between the nerve subtypes. The PCA plot suggested some separation of the nerve subtypes into four classes which corresponded with the nerve types. This was supported by the K-means clustering. Some overlap in classes was noted in these two clustering analyses. This study provides emerging evidence that DESI-MSI is an effective tool for metabolomic profiling of peripheral nerves. Our results suggest that peripheral nerves have molecular profiles that are distinct from the surrounding connective tissues and that DESI-MSI may be able to discriminate between nerve subtypes. DESI-MSI of peripheral nerves may be a valuable technique that could be used to improve our understanding of peripheral nerve anatomy and physiology. The ability to utilize ambient mass spectrometry techniques in real time could also provide an unprecedented advantage for surgical decision making, including in nerve-sparing procedures in the future.

Next-generation pathology practices with mass spectrometry imaging

Mass spectrometry imaging (MSI) is a powerful technique that reveals the spatial distribution of various molecules in biological samples, and it is widely used in pathology-related research. In this review, we summarize common MSI techniques, including matrix-assisted laser desorption/ionization and desorption electrospray ionization MSI, and their applications in pathological research, including disease diagnosis, microbiology, and drug discovery. We also describe the improvements of MSI, focusing on the accumulation of imaging data sets, expansion of chemical coverage, and identification of biological significant molecules, that have prompted the evolution of MSI to meet the requirements of pathology practices. Overall, this review details the applications and improvements of MSI techniques, demonstrating the potential of integrating MSI techniques into next-generation pathology practices.

Point-of-care applicable metabotyping using biofluid-specific electrospun MetaSAMPs directly amenable to ambient LA-REIMS

In recent years, ambient ionization mass spectrometry (AIMS) including laser ablation rapid evaporation IMS, has enabled direct biofluid metabolome analysis. AIMS procedures are, however, still hampered by both analytical, i.e., matrix effects, and practical, i.e., sample transport stability, drawbacks that impede metabolome coverage. In this study, we aimed at developing biofluid-specific metabolome sampling membranes (MetaSAMPs) that offer a directly applicable and stabilizing substrate for AIMS. Customized rectal, salivary, and urinary MetaSAMPs consisting of electrospun (nano)fibrous membranes of blended hydrophilic (polyvinylpyrrolidone and polyacrylonitrile) and lipophilic (polystyrene) polymers supported metabolite absorption, adsorption, and desorption. Moreover, MetaSAMP demonstrated superior metabolome coverage and transport stability compared to crude biofluid analysis and was successfully validated in two pediatric cohorts (MetaBEAse, n = 234 and OPERA, n = 101). By integrating anthropometric and (patho)physiological with MetaSAMP-AIMS metabolome data, we obtained substantial weight-driven predictions and clinical correlations. In conclusion, MetaSAMP holds great clinical application potential for on-the-spot metabolic health stratification.

Moving beyond DNA: towards functional analysis of the vaginal microbiome by non-sequencing-based methods

Over the last two decades, sequencing-based methods have revolutionised our understanding of niche-specific microbial complexity. In the lower female reproductive tract, these approaches have enabled identification of bacterial compositional structures associated with health and disease. Application of metagenomics and metatranscriptomics strategies have provided insight into the putative function of these communities but it is increasingly clear that direct measures of microbial and host cell function are required to understand the contribution of microbe-host interactions to pathophysiology. Here we explore and discuss current methods and approaches, many of which rely upon mass-spectrometry, being used to capture functional insight into the vaginal mucosal interface. In addition to improving mechanistic understanding, these methods offer innovative solutions for the development of diagnostic and therapeutic strategies designed to improve women's health.

Rectal swabs as a viable alternative to faecal sampling for the analysis of gut microbiota functionality and composition

Faecal or biopsy samples are frequently used to analyse the gut microbiota, but issues remain with the provision and collection of such samples. Rectal swabs are widely-utilised in clinical practice and previous data demonstrate their potential role in microbiota analyses; however, studies to date have been heterogenous, and there are a particular lack of data concerning the utility of swabs for the analysis of the microbiota's functionality and metabolome. We compared paired stool and rectal swab samples from healthy individuals to investigate whether rectal swabs are a reliable proxy for faecal sampling. There were no significant differences in key alpha and beta diversity measures between swab and faecal samples, and inter-subject variability was preserved. Additionally, no significant differences were demonstrated in abundance of major annotated phyla. Inferred gut functionality using Tax4Fun2 showed excellent correlation between the two sampling techniques (Pearson's coefficient r = 0.9217, P < 0.0001). Proton nuclear magnetic resonance (¹H NMR) spectroscopy enabled the detection of 20 metabolites, with overall excellent correlation identified between rectal swab and faecal samples for levels all metabolites collectively, although more variable degrees of association between swab and stool for levels of individual metabolites. These data support the utility of rectal swabs in both compositional and functional analyses of the gut microbiota.

Cutting-edge strategies and critical advancements in characterization and quantification of metabolites concerning translational metabolomics

Despite remarkable progress in drug discovery strategies, significant challenges are still remaining in translating new insights into clinical applications. Scientists are devising creative approaches to bridge the gap between scientific and translational research. Metabolomics is a unique field among other omics techniques for identifying novel metabolites and biomarkers. Fortunately, characterization and quantification of metabolites are becoming faster due to the progress in the field of orthogonal analytical techniques. This review detailed the advancement in the progress of sample preparation, and data processing techniques including data mining tools, database, and their quality control (QC). Advances in data processing tools make it easier to acquire unbiased data that includes a diverse set of metabolites. In addition, novel breakthroughs including, miniaturization as well as their integration with other devices, metabolite array technology, and crystalline sponge-based method have led to faster, more efficient, cost-effective, and holistic metabolomic analysis. The use of cutting-edge techniques to identify the human metabolite, including biomarkers has proven to be advantageous in terms of early disease identification, tracking the progression of illness, and possibility of personalized treatments. This review addressed the constraints of current metabolomics research, which are impeding the facilitation of translation of research from bench to bedside. Nevertheless, the possible way out from such constraints and future direction of translational metabolomics has been conferred.

Mass Spectrometry Imaging technology in metabolomics: a systematic review

Mass spectrometry imaging (MSI) is a powerful label-free analysis technique that can provide simultaneous spatial distribution of multiple compounds in a single experiment. By combining the sensitive and rapid screening of high-throughput mass spectrometry with spatial chemical information, metabolite analysis and morphological characteristics are presented in a single image. MSI can be used for qualitative and quantitative analysis of metabolic profiles and it can provide visual analysis of spatial distribution information of complex biological and microbial systems. Matrix assisted laser desorption ionization, laser ablation electrospray ionization and desorption electrospray ionization are commonly used in MSI. Here, we summarize and compare these three technologies, as well as the applications and prospects of MSI in metabolomics.

Liquid extraction surface analysis-mass spectrometry: An advanced and environment-friendly analytical tool in modern analysis

The Liquid Extraction Surface Analysis technique is a new high-throughput instrument for ambient mass spectrometry. The benefits of the Liquid Extraction Surface Analysis-Mass Spectrometry approach are the high throughput screening of samples and the absence of sample preparation. Liquid Extraction Surface Analysis-Mass Spectrometry also consumes less solvent for extraction, making it more environmentally friendly and there is no substrate restriction. It utilizes advanced instrumentation like the use of robotic pipettes, nanoelectrospray systems, electronspray ionization chips which makes it highly efficient. In recent years, Liquid Extraction Surface Analysis-Mass Spectrometry has seen widespread use in a variety of analytical fields including drug metabolite analysis, mapping drug distribution in tissues, protein and lipid characterization etc. In this review, we have summarized the basic working principles of the Liquid Extraction Surface Analysis-Mass Spectrometry approach in detail along with a detailed description of the recently reported applications in the analysis of proteins, lipids, drugs and foods. The investigated analytes along with detection methodologies and significant outcomes of various research reports have been presented with the help of tables. This tool has also been utilized in clinical investigations of biological fluids, fingerprint analysis and authentication of agarwood. This article is protected by copyright. All rights reserved.

Direct on-swab metabolic profiling of vaginal microbiome host interactions during pregnancy and preterm birth

The pregnancy vaginal microbiome contributes to risk of preterm birth, the primary cause of death in children under 5 years of age. Here we describe direct on-swab metabolic profiling by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) for sample preparation-free characterisation of the cervicovaginal metabolome in two independent pregnancy cohorts (VMET, n = 160; 455 swabs; VMET II, n = 205; 573 swabs). By integrating metataxonomics and immune profiling data from matched samples, we show that specific metabolome signatures can be used to robustly predict simultaneously both the composition of the vaginal microbiome and host inflammatory status. In these patients, vaginal microbiota instability and innate immune activation, as predicted using DESI-MS, associated with preterm birth, including in women receiving cervical cerclage for preterm birth prevention. These findings highlight direct on-swab metabolic profiling by DESI-MS as an innovative approach for preterm birth risk stratification through rapid assessment of vaginal microbiota-host dynamics.

Bacterial Vaginosis: Current Diagnostic Avenues and Future Opportunities

A healthy female genital tract harbors a microbiome dominated by lactic acid and hydrogen peroxide producing bacteria, which provide protection against infections by maintaining a low pH. Changes in the bacterial compositions of the vaginal microbiome can lead to bacterial vaginosis (BV), which is often associated with vaginal inflammation. Bacterial vaginosis increases the risk of acquiring sexually transmitted infections (STIs) like human immunodeficiency virus (HIV) and affects women's reproductive health negatively. In pregnant women, BV can lead to chorioamnionitis and adverse pregnancy outcomes, including preterm premature rupture of the membranes and preterm birth. In order to manage BV effectively, good diagnostic procedures are required. Traditionally clinical and microscopic methods have been used to diagnose BV; however, these methods require skilled staff and time and suffer from reduced sensitivity and specificity. New diagnostics, including highly sensitive and specific point-of-care (POC) tests, treatment modalities and vaccines can be developed based on the identification of biomarkers from the growing pool of vaginal microbiome and vaginal metabolome data. In this review the current and future diagnostic avenues will be discussed.

Coulometry-assisted quantitation in spray ionization mass spectrometry

The concentration of target analyte in a mixture can be quantified by combining coulometric measurements with spray ionization mass spectrometry. A three-electrode system screen printed on the polymer support acts both as the coulometry platform for electrochemical oxidation and the sample loading tip for spray ionization. After loading a droplet of the analyte solution onto the tip, two steps were taken to implement quantitation. First, the electrochemical oxidation potential was optimized with cyclic voltammetry followed by coulometric measurements to calculate the amount of oxidized analyte under a constant low voltage within a fixed period of time (5 s). Then, a high voltage (+4.5 kV) was applied to the tip to trigger spray ionization for measuring the oxidation yield from the native analyte ion and its oxidized product ion intensities by mass spectrometry. The analyte's native concentration is quantified by dividing the oxidized product's concentration (based on Coulomb's law) and the oxidation yield (estimated from mass spectrometry [MS] assuming that the parent and oxidation product have nearly the same ionization efficiencies). The workflow has an advantage in being free of any standard for constructing the quantitation curve. Several model compounds (tyrosine, dopamine, and angiotensin II) were selected for method validation. It was demonstrated that this strategy was feasible with an accuracy of ~15% for a wide coverage of different species including endogenous metabolites and peptides. As an example of its possible practical use, it was initially employed to make a bilirubin assay in urine.

Direct identification of bacterial and human proteins from infected wounds in living 3D skin models

Trauma is one of the leading causes of death in people under the age of 49 and complications due to wound infection are the primary cause of death in the first few days after injury. The ESKAPE pathogens are a group of bacteria that are a leading cause of hospital-acquired infections and a major concern in terms of antibiotic resistance. Here, we demonstrate a novel and highly accurate approach for the rapid identification of ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) directly from infected wounds in 3D in vitro skin models. Wounded skin models were inoculated with bacteria and left to incubate. Bacterial proteins were identified within minutes, directly from the wound, by liquid extraction surface analysis mass spectrometry. This approach was able to distinguish closely related strains and, unlike genomic approaches, can be modified to provide dynamic information about pathogen behaviour at the wound site. In addition, since human skin proteins were also identified, this method offers the opportunity to analyse both host and pathogen biomarkers during wound infection in near real-time.

In vivo solid-phase microextraction swab sampling of environmental pollutants and drugs in human body for nano-electrospray ionization mass spectrometry analysis

In vivo sampling and sensitive detection of environmental pollutants and drugs in human body play a crucial role in understanding human health. In this study, in vivo solid-phase microextraction (SPME) swab was fabricated using a SPME fiber and a medical cotton swab for noninvasive sampling and extraction of environmental pollutants and drugs in human oral cavity, nasal cavity and on skin surface. After sampling, SPME was coupled with nano-electrospray ionization mass spectrometry (nanoESI-MS) for desorption, ionization, and detection of the extracted analytes. As a result, limit of detection (LOD) and limit of quantification (LOQ) of nicotine in oral fluid were found to be 1.0 pg/mL (S/N ≥ 3) and 4.0 pg/mL (S/N ≥ 10), respectively. Linear dynamic signal responses of nicotine exhibited excellent linearity (R² = 0.9996) in human oral fluid ranging from 0.1 to 50 ng/mL. The coefficient of variation (CV) values of SPME swab for five measurements from sample vials and human body were 5.1-6.7% and 22.7-32.6%, respectively. Rapid analysis of a single sample could be completed within 10 min. Overall, our results demonstrated that SPME swab-MS is a promising noninvasive method for enhanced detection of analytes in human body.

Applications of Mass Spectrometry for Clinical Diagnostics: The Influence of Turnaround Time

This critical review discusses how the need for reduced clinical turnaround times has influenced chemical instrumentation. We focus on the development of modern mass spectrometry (MS) and its application in clinical diagnosis. With increased functionality that takes advantage of novel front-end modifications and computational capabilities, MS can now be used for non-traditional clinical analyses, including applications in clinical microbiology for bacteria differentiation and in surgical operation rooms. We summarize here recent developments in the field that have enabled such capabilities, which include miniaturization for point-of-care testing, direct complex mixture analysis via ambient ionization, chemical imaging and profiling, and systems integration.

An update on the routine application of MALDI-TOF MS in clinical microbiology

Introduction: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has entered clinical diagnostics and is today a generally accepted and integral part of the workflow for microbial identification. MALDI-TOF MS identification systems received approval from national and international institutions, such as the USA-FDA, and are continuously improved and adopted to other fields like veterinary and industrial microbiology. The question is whether MALDI-TOF MS also has the potential to replace other conventional and molecular techniques operated in routine diagnostic laboratories. Areas covered: We give an overview of new advancements of mass spectral analysis in the context of microbial diagnostics. In particular, the expansion of databases to increase the range of readily identifiable bacteria and fungi, the refined discrimination of species complexes, subspecies, and types, the testing for antibiotic resistance or susceptibility, progress in sample preparation including automation, and applications of other mass spectrometry techniques are discussed. Expert opinion: Although many new approaches of MALDI-TOF MS are still in the stage of proof of principle, it is expectable that MALDI-TOF MS will expand its role in the clinical microbiology laboratory of the future. New databases, instruments and analytical software modules will continue to be developed to further improve diagnostic efficacy.

Establishment of vaginal microbiota composition in early pregnancy and its association with subsequent preterm prelabor rupture of the fetal membranes

Vaginal bacterial community composition influences pregnancy outcome. Preterm prelabor rupture of the fetal membranes (PPROM), which precedes 30% of all spontaneous preterm births, is associated with high vaginal bacterial diversity prior to rupture. The point at which vaginal bacterial diversity is established before PPROM is unknown. In this study, we use metataxonomics to longitudinally characterize the vaginal bacterial composition from as early as 6 weeks of gestation in women at high (n = 38) and low (n = 22) risk of preterm birth who subsequently experience PPROM and in women delivering at term without complications (n = 36). Reduced Lactobacillus spp. abundance and high diversity was observed prior to PPROM in 20% and 26% of women at low and high risk of preterm births respectively, but in only 3% of women who delivered at term. PPROM was associated with instability of bacterial community structure during pregnancy and a shift toward higher diversity predominately occurring during the second trimester. This was characterized by increased relative abundance of potentially pathogenic species including Prevotella, Peptoniphilus, Streptococcus, and Dialister. This study identifies reduced Lactobacillus spp. abundance and increasing vaginal bacterial diversity as an early risk factor for PPROM and highlights the need for interventional studies designed to assess the impact of modifying vaginal bacterial composition for the prevention of preterm birth.

Ecological dynamics of the vaginal microbiome in relation to health and disease

The bacterial composition of the vaginal microbiome is thought to be related to health and disease states of women. This microbiome is particularly dynamic, with compositional changes related to pregnancy, menstruation, and disease states such as bacterial vaginosis. In order to understand these dynamics and their impact on health and disease, ecological theories have been introduced to study the complex interactions between the many taxa in the vaginal bacterial ecosystem. The goal of this review is to introduce the ecological principles that are used in the study of the vaginal microbiome and its dynamics, and to review the application of ecology to vaginal microbial communities with respect to health and disease. Although applications of vaginal microbiome analysis and modulation have not yet been introduced into the routine clinical setting, a deeper understanding of its dynamics has the potential to facilitate development of future practices, for example in the context of postmenopausal vaginal symptoms, stratifying risk for obstetric complications, and controlling sexually transmitted infections.

Prospective observational study of vaginal microbiota pre- and post-rescue cervical cerclage

OBJECTIVE

To investigate the relation between vaginal microbiota composition and outcome of rescue cervical cerclage.

DESIGN

Prospective observational study.

SETTING

Queen Charlotte's and Chelsea Hospital, London.

POPULATION

Twenty singleton pregnancies undergoing a rescue cervical cerclage.

METHODS

Vaginal microbiota composition was analysed in women presenting with a dilated cervix and exposed fetal membranes before and 10 days following rescue cervical cerclage and was correlated with clinical outcomes.

MAIN OUTCOME MEASURES

Composition of vaginal bacteria was characterised by culture-independent next generation sequencing. Successful cerclage was defined as that resulting in the birth of a neonate discharged from hospital without morbidity. Unsuccessful cerclage was defined as procedures culminating in miscarriage, intrauterine death, neonatal death or significant neonatal morbidity.

RESULTS

Reduced Lactobacillus spp. relative abundance was observed in 40% of cases prior to rescue cerclage compared with 10% of gestation age-matched controls (8/20, 40% versus 3/30, 10%, P = 0.017). Gardnerella vaginalis was over-represented in women presenting with symptoms (3/7, 43% versus 0/13, 0%, P = 0.03, linear discriminant analysis, LDA (log 10) and cases culminating in miscarriage (3/6, 50% versus 0/14, 0%, P = 0.017). In the majority of cases (10/14, 71%) bacterial composition was unchanged following cerclage insertion and perioperative interventions.

CONCLUSIONS

Reduced relative abundance of Lactobacillus spp. is associated with premature cervical dilation, whereas high levels of G. vaginalis are associated with unsuccessful rescue cerclage cases. The insertion of a rescue cerclage does not affect the underlying bacterial composition in the majority of cases.

TWEETABLE ABSTRACT

Preterm cervical dilatation associates with reduced Lactobacillus spp. Presence of Gardnerella vaginalis predicts rescue cerclage failure.

Assessment of microbiota:host interactions at the vaginal mucosa interface

There is increasing appreciation of the role that vaginal microbiota play in health and disease throughout a woman's lifespan. This has been driven partly by molecular techniques that enable detailed identification and characterisation of microbial community structures. However, these methods do not enable assessment of the biochemical and immunological interactions between host and vaginal microbiota involved in pathophysiology. This review examines our current knowledge of the relationships that exist between vaginal microbiota and the host at the level of the vaginal mucosal interface. We also consider methodological approaches to microbiomic, immunologic and metabolic profiling that permit assessment of these interactions. Integration of information derived from these platforms brings the potential for biomarker discovery, disease risk stratification and improved understanding of the mechanisms regulating vaginal microbial community dynamics in health and disease.

The human female urogenital microbiome: complexity in normality

Microbial communities of the urogenital tract have long been recognised to play an important role in disease states. A revolution in methodological approaches is permitting the assessment of complex urogenital tract microbiota-host interactions and the metabolic and protein milieu of the mucosal interface. There is now great potential for significant advances in biomarker discovery and disease risk stratification, and for the elucidation of mechanisms underpinning the microbial community dynamics involved in urogenital tract pathology. Microbiota-host interactions in the female genital tract have a particular significance, because unlike in the male, there is direct communication between the external genitalia, the uterus and the peritoneal cavity. This review examines the microbial community composition at differing sites of the female urogenital tract and its relationship with health and disease. Key factors involved in the modulation of vaginal microbiome stability and structure, such as endocrine, immune and inflammatory pathways, are considered in the context of a woman's life cycle and disease pathogenesis.

Quantitative analysis of biofluid spots by coated blade spray mass spectrometry, a new approach to rapid screening

This study demonstrates the quantitative capabilities of coated blade spray (CBS) mass spectrometry (MS) for the concomitant analysis of multiple target substances in biofluid spots. In CBS-MS the analytes present in a given sample are first isolated and enriched in the thin coating of the CBS device. After a quick rinsing of the blade surface, as to remove remaining matrix, the analytes are quickly desorbed with the help of a solvent and then directly electrosprayed into the MS analyzer. Diverse pain management drugs, controlled substances, and therapeutic medications were successfully determined using only 10 µL of biofluid, with limits of quantitation in the low/sub ng·mL⁻¹ level attained within 7 minutes.

Themis: Batch Preprocessing for Ultrahigh-Resolution Mass Spectra of Complex Mixtures

Fourier transform ion cyclotron resonance mass spectrometry affords the resolving power to determine an unprecedented number of components in complex mixtures, such as petroleum. The software tools required to also analyze these data struggle to keep pace with advancing instrument capabilities and increasing quantities of data, particularly in terms of combining information efficiently across multiple replicates. Improved confidence in data and the use of replicates is particularly important where strategic decisions will be based upon the analysis. We present a new algorithm named Themis, developed using R, to jointly preprocess replicate measurements of a sample with the aim of improving consistency as a preliminary step to assigning peaks to chemical compositions. The main features of the algorithm are quality control criteria to detect failed runs, ensuring comparable magnitudes across replicates, peak alignment, and the use of an adaptive mixture model-based strategy to help distinguish true peaks from noise. The algorithm outputs a list of peaks reliably observed across replicates and facilitates data handling by preprocessing all replicates in a single step. The processed data produced by our algorithm can subsequently be analyzed by use of relevant specialized software. While Themis has been demonstrated with petroleum as an example of a complex mixture, its basic framework will be useful for complex samples arising from a variety of other applications.

Internal Energy Deposition in Dielectric Barrier Discharge Ionization is Significantly Lower than in Direct Analysis in Real-Time Mass Spectrometry

The extent of internal energy deposition using three different plasma-based ionization mass spectrometry (MS) methods, atmospheric pressure chemical ionization (APCI), direct analysis in real time (DART), and active capillary dielectric barrier discharge ionization (DBDI), was investigated using benzylammonium ‘thermometer’ ions. Ions formed by DBDI were activated significantly less than those that were formed by DART and APCI under these conditions. Thermal ion activation by DART can be reduced slightly by positioning the DART source further from the capillary entrance to the MS and reducing the heat that is applied to metastable atoms exiting the DART source. For example, the average ion internal energy distribution decreased by less than 10 % (166.9 ± 0.3 to 152.2 ± 1.0 kJ mol−1) when the distance between the DART source and the MS was increased by 250 % (10 to 25 mm). By lowering the DART temperature from 350 to 150°C, the internal energy distributions of the thermometer ions decreased by ~15 % (169.93 ± 0.83 to 150.21 ± 0.52 kJ mol−1). Positioning the DART source nozzle more than 25 mm from the entrance to the MS and decreasing the DART temperature further resulted in a significant decrease in ion signal. Thus, varying the major DART ion source parameters had minimal impact on the ‘softness’ of the DART ion source under these conditions. Overall, these data indicate that DBDI can be a significantly ‘softer’ ion source than two of the most widely used plasma-based ion sources that are commercially available.