Selected Ion Flow Tube Research Articles

Atomization of As and Se volatile species in a dielectric barrier discharge atomizer after hydride generation: Fate of analyte studied by selected ion flow tube mass spectrometry

Atomization of hydrides and their methylated analogues in a dielectric barrier discharge (DBD) plasma atomizer was investigated. Selected ion flow tube mass spectrometry (SIFT-MS) was chosen as a detector being capable of selective detection of non-atomized original volatile species allowing thus direct quantification of atomization efficiency. Selenium hydride (SeH2) and three volatile arsenic species, namely arsenic hydride (AsH3), monomethylarsane (CH3AsH2) and dimethylarsane ((CH3)2AsH), were selected as model analytes. The mechanistic study performed contributes to understanding of the atomization processes in atomic absorption spectrometry (AAS). The presented results are compatible with a complete atomization of arsenic hydride as well as its methylated analogues and with atomization efficiency of SeH2 below 80%. Using AsH3 as a model analyte and a combination of AAS and SIFT-MS detectors has revealed that the hydride is not atomized, but decomposed in the DBD atomizer in absence of hydrogen fraction in the carrier gas. Apart from investigation of analyte atomization, the SIFT-MS detector is capable of quantitative determination of water vapor content being either transported to, or produced in the atomizer. This information is crucial especially in the case of the low-power/temperature DBD atomizer since its performance is sensitive to the amount of water vapor introduced into the plasma.

Source apportionment and quantification of liquid and headspace leaks from closed system drug-transfer devices via Selected Ion Flow Tube Mass Spectrometry (SIFT-MS).

A system to differentiate and quantify liquid and headspace vapor leaks from closed system drug-transfer devices (CSTDs) is presented. CSTDs are designed to reduce or eliminate hazardous drug (HD) exposure risk when compounding and administering HDs. CSTDs may leak liquid, headspace, or a mixture of the two. The amount of HD contained in liquid and headspace leaks may be substantially different. Use of a test solution containing two VOCs with differences in ratios of VOC concentrations in the headspace and liquid enables source apportionment of leaked material. SIFT-MS was used to detect VOCs from liquid and headspace leaks in the vapor phase. Included in this report is a novel method to determine the origin and magnitude of leaks from CSTDs. A limit of leak detection of 24 μL of headspace vapor and 0.14 μL of test liquid were found using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS).

The breath print represents a novel biomarker of malnutrition in pulmonary arterial hypertension: A proof of concept study.

The breath print is a quantitative measurement of molecules in exhaled breath and represents a new frontier for biomarker identification. It is unknown whether this state-of-the-art, noninvasive method can detect malnutrition. We hypothesize that individuals with malnutrition will present with a distinguishable breath print. We conducted a retrospective chart review on patients with previously analyzed breath samples to identify malnutrition. Breath was analyzed by selected-ion flow-tube mass spectrometry. Registered dietitians conducted a retrospective chart review to collect malnutrition diagnoses and nutrition status indicators. Patients were categorized into one of four groups: pulmonary arterial hypertension (PAH), PAH with malnutrition (PAH-Mal), control, and control with malnutrition (Control-Mal), based on the malnutrition diagnosis present in the patient's chart. Principle component analysis was conducted to characterize the breath print. A logistic regression model with forward selection was used to detect the best breath predictor combination of malnutrition. A total of 74 patients met inclusion criteria (PAH: 52; PAH-Mal: 10; control: 10; Control-Mal: 2). Levels of 1-octene (PAH-Mal, 5.1 ± 1.2; PAH, 12.5 ± 11.2; P = 0.005) and ammonia (PAH-Mal, 14.6 ± 15.8; PAH, 56.2 ± 64.2; P = 0.013) were reduced in PAH-Mal compared with PAH. The combination of 1-octene (P = 0.010) and 3-methylhexane (P = 0.045) distinguished malnutrition in PAH (receiver operating characteristic area under the curve: 0.8549). This proof of concept study provides the first evidence that the breath print is altered in malnutrition. Larger prospective studies are needed to validate these results and establish whether breath analysis may be a useful tool to screen for malnutrition in the clinical setting.

Cyclotrimerization of Acetylene under Thermal Conditions: Gas-Phase Kinetics of V+ and Fe+ + C2H2.

The kinetics of successive reactions of acetylene (C2H2) initiated on either vanadium or iron atomic cations have been investigated under thermal conditions using the variable-ion source and temperature-adjustable selected-ion flow tube apparatus. Consistent with the literature results, the reaction of Fe+ + C2H2 primarily yields Fe+(m/z = (C2H2)3); however, analysis via quantum chemical calculations and statistical modeling shows that the mechanism does not form benzene upon the third acetylene addition. The kinetics are more consistent with successive addition of three acetylene molecules, yielding Fe+(C2H2)3, followed by an addition of a fourth acetylene molecule, initiating cyclotrimerization, yielding either Fe+(C2H2) + neutral benzene or Fe+(Bz) + acetylene, where Bz is a benzene ligand. In contrast, the reaction of V+ + C2H2 yields products via successive associations V+(m/z = (C2H2)n) either with or without a bimolecular step involving loss of one H2 and V+C2(m/z = (C2H2)m), where n and m extend at least up to 11 under conditions of 0.32 Torr at 300 K. Stabilized V+(Bz) is not a significant intermediate in the association mechanism. We propose a plausible mechanism for the generation of neutral benzene in this reaction and compare with the Fe+ results. The reaction steps that produce benzene result in turnover of the single-atom catalyst, and the large hydrocarbons produced that remain associated to the catalyst are proposed to be polycyclic aromatic hydrocarbons.

Multi-component ppm level adsorption of VOCs on the ZIF-8 and UiO-66 MOFs: Breakthrough analysis with selected ion flow tube mass spectrometry

In the recent years, Metal-Organic Frameworks (MOFs) emerged at a high and increasing pace and have been widely studied in the frame of applications such as gas storage, mixtures separation and heterogeneous catalysis. Nevertheless, the study of Volatile Organic Compounds (VOCs) adsorption on Metal-Organic Frameworks (MOFs) is still lagging behind compared to zeolites and other conventional adsorbent materials. The selection of an optimal adsorbent for the trapping of environmental VOCs, only present at ppmv levels, strongly relies on its low-coverage adsorption properties, which are often challenging to evaluate through conventional experimental methods. In this work, adsorption of VOCs on Metal-Organic Frameworks (MOFs) was investigated using a novel experimental methodology to measure breakthrough adsorption at ultra-low concentration amid 4–12 ppmv. Multicomponent breakthrough curves of a mixture of ethanol, ethyl acetate, 2-butanone and 2,3-butanedione were measured in anhydrous condition at 25 °C and 6 °C on two highly stable MOFs, namely ZIF-8 and UiO-66, using Selected Ions Flow Tube Mass Spectrometry (SIFT-MS) for monitoring. Furthermore, adsorption experiments were carried out at 6 °C and 90% RH to evaluate the effect of humidity on the VOCs uptake onto the selected MOFs. While ZIF-8 adsorption capacities were ranging between 0.3 and 1.8 mg g−1, UiO-66 exhibited significantly higher uptake towards the target compounds, with a concentration comprised between 1.8 and 51.9 mg g−1. Despite this relevant discrepancy, both MOFs shared a pronounced preferentiality towards the most hydrophobic molecules. Very large enrichment factors (between 100 and 5000) showed that these materials can increase many-fold the adsorbed phase over gas phase concentration, even when present at ppmv levels, which is crucial for the good operation of sensors based on affinity layers. Furthermore, VOCs adsorption on UiO-66 unveils intricate competitive mechanisms, leading to multiple steps of ethanol displacement while simultaneous adsorption of ethyl acetate, 2-butanon and 2,3-butanedione occurs.

Sensitivity of secondary electrospray ionization mass spectrometry to a range of volatile organic compounds: Ligand switching ion chemistry and the influence of Zspray™ guiding electric fields.

Secondary electrospray ionization (SESI) is currently only semi-quantitative. In the Zspray™ arrangement of SESI-MS, the transfer of ions from near atmospheric pressure to a triple quadrupole is achieved by guiding electric fields that partially desolvate both reagent and analyte ions which must be understood. Also, to make SESI-MS more quantitative, the mechanisms and the kinetics of the reaction processes, especially ligand switching reactions of hydrated hydronium reagent ions, H3 O+ (H2 O)n , with volatile organic compound (VOC) molecules, need to be understood. A modified Zspray™ ESI ion source operating at sub-atmospheric pressure with analyte sample gas introduced via an inlet coaxial with the spray was used. Variation of the ion-guiding electric fields was used to reveal the degree of desolvation of both reagent and analyte ions. The instrument sensitivity was determined for several classes of VOCs by introducing bag samples of suitably varying concentrations as quantified on-line using selected ion flow tube MS. Electric field desolvation resulted in largely protonated VOCs, MH+ , and their monohydrates, MH+ H2 O, and for some VOCs proton-bound dimer ions, MH+ M, were formed. There was a highly linear response of the ion signal to the measured VOC sample concentration, which provided the instrument sensitivities, S, for 25 VOCs. The startling results show very wide variations in S from near 0 to 1 for hydrocarbons, and up to 100, on a relative scale, for polar compounds such as monoketones and unsaturated aldehydes. The complex ion chemistry occurring in the SESI ion source, largely involving gas-phase ligand switching, results in widely variable sensitivities for different classes of VOCs. The sensitivity is observed to depend on the dipole moment and proton affinity of the analyte VOC molecule, M, and to decrease with the observed fraction of MH+ H2 O, but other yet unrecognized factors must play a significant role.

The peppermint breath test benchmark for PTR-MS and SIFT-MS

A major challenge for breath research is the lack of standardization in sampling and analysis. To address this, a test that utilizes a standardized intervention and a defined study protocol has been proposed to explore disparities in breath research across different analytical platforms and to provide benchmark values for comparison. Specifically, the Peppermint Experiment involves the targeted analysis in exhaled breath of volatile constituents of peppermint oil after ingestion of the encapsulated oil. Data from the Peppermint Experiment performed by proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS) are presented and discussed herein, including the product ions associated with the key peppermint volatiles, namely limonene, α- and β-pinene, 1,8-cineole, menthol, menthone and menthofuran. The breath washout profiles of these compounds from 65 individuals were collected, comprising datasets from five PTR-MS and two SIFT-MS instruments. The washout profiles of these volatiles were evaluated by comparing the log-fold change over time of the product ion intensities associated with each volatile. Benchmark values were calculated from the lower 95% confidence interval of the linear time-to-washout regression analysis for all datasets combined. Benchmark washout values from PTR-MS analysis were 353 min for the sum of monoterpenes and 1,8-cineole (identical product ions), 173 min for menthol, 330 min for menthofuran, and 218 min for menthone; from SIFT-MS analysis values were 228 min for the sum of monoterpenes, 281 min for the sum of monoterpenes and 1,8-cineole, and 370 min for menthone plus 1,8-cineole. Large inter- and intra-dataset variations were observed, whereby the latter suggests that biological variability plays a key role in how the compounds are absorbed, metabolized and excreted from the body via breath. This variability seems large compared to the influence of sampling and analytical procedures, but further investigations are recommended to clarify the effects of these factors.

Diagnosis of Clostridioides difficile infection by analysis of volatile organic compounds in breath, plasma, and stool: A cross-sectional proof-of-concept study.

Clostridioides difficile infection (CDI) is an important infectious cause of antibiotic-associated diarrhea, with significant morbidity and mortality. Current diagnostic algorithms are based on identifying toxin by enzyme immunoassay (EIA) and toxin gene by real-time polymerase chain reaction (PCR) in patients with diarrhea. EIA's sensitivity is poor, and PCR, although highly sensitive and specific, cannot differentiate infection from colonization. An ideal test that incorporates microbial factors, host factors, and host-microbe interaction might characterize true infection, and assess prognosis and recurrence. The study of volatile organic compounds (VOCs) has the potential to be an ideal diagnostic test. The presence of VOCs accounts for the characteristic odor of stool in CDI but their presence in breath and plasma has not been studied yet. A cross-sectional proof-of-concept study analyzing VOCs using selected ion flow tube mass spectrometry (SIFT-MS) was done on breath, stool, and plasma of patients with clinical features and positive PCR for CDI (cases) and compared with patients with clinical features but a negative PCR (control). Our results showed that VOC patterns in breath, stool, and plasma, had good accuracy [area under the receiver operating characteristic curve (ROC) 93%, 86%, and 91%, respectively] for identifying patients with CDI.

Chemical ionization of carboxylic acids and esters in negative mode selected ion flow tube – Mass spectrometry (SIFT-MS)

Selected ion flow tube – mass spectrometry (SIFT-MS) is based on chemical reactivity of analytes with reactant ions. The complete understanding of all the ion–molecule reactions is the key to the deployment of this technology for the direct and rapid analysis of VOCs in the gas phase. In the present work, we focused on direct analysis of carboxylic acids and esters, compounds involved in many biochemical processes.The ion–molecule reactions of negative precursor ions (OH–, O●−, O2●−, NO2– and NO3–) with 9 carboxylic acids and 21 esters were investigated in order to provide product ions and rate constants for these compounds analysis by SIFT-MS. The modelling of ion–molecule reaction paths by ab-initio calculations supported the experimental results and provided a better understanding of these gas phase ion–molecule reactions.The most common reaction mechanism with all the tested molecules is deprotonation. However, other specific reactivities, leading to the formation of anion-molecule complexes with NO2– and O2●− in particular, are observed. Furthermore, specific fragmentations of chemical families are also noticed and confirmed with O2●− and O●−. Finally, we demonstrated that the composition of the matrix (H2O, CO2) participates in the formation of secondary ions.In this work, we determined the kinetic rate constants in the nitrogen carrier gas and the detection limits of all the compounds with the eight precursor ions used by SIFT-MS, allowing accurate quantification in the gas phase at the ppb level. These results contribute to enlarge the negative ionization SIFT-MS measurements to applications where quantification of organic acids and esters are required.

Metal Ionization in Sub-atmospheric Pressure MALDI Interface: A New Tool for Mass Spectrometry of Volatile Organic Compounds.

A novel approach for the analysis of volatile organic compounds (VOCs) based on chemical ionization by Au+ ions has been proposed. The ionization is carried out in a commercially available dual sub-atmospheric pressure MALDI/ESI interface without any modifications. The Au+ ions are generated by laser ablation of a gold nanolayer with the MALDI laser, and VOCs are infused via the ESI capillary. The ultrahigh resolving power and sub-ppm mass accuracy of the employed mass spectrometer allow straightforward identification of the formed ion-molecule complexes and other products of Au+ interactions with VOCs in the gas phase. The performance of the technique is demonstrated on the analysis of various classes of organic molecules, namely, alkanes, alkenes, alcohols, aldehydes, ketones, aromatic compounds, carboxylic acids, ethers, or organosulfur compounds, expanding the portfolio of currently available methods for the analysis of VOCs such as secondary electrospray ionization, proton-transfer reaction, and selected ion flow tube mass spectrometry.

A Study on Reliability Improvement of Management for Air Pollution Emission Sources Using Selected Ion Flow Tube Mass Spectrometers

A Study on Reliability Improvement of Management for Air Pollution Emission Sources Using Selected Ion Flow Tube Mass Spectrometers

Heat-induced compounds development in processed tomato and their influence on corrosion initiation in metal food cans.

Selected ion flow tube mass spectrometry (SIFT‐MS) and ion chromatography (IC) were used to investigate the presence of volatile and nonvolatile compounds in canned tomatoes and in the polymeric lining before and after retorting the cans. This allowed us to observe if these compounds contributed to corrosion and the migration of iron and tin compounds from the cans to the tomatoes. Diced Roma tomatoes and other simulant treatment groups were sealed in two‐piece tinplated cans (controls in glass jars), retorted at 121℃ for 30 min, then stored at 49℃ for 50 days. Results showed that thermal degradation of amino acids in the tomatoes gave rise to volatile methyl sulfides and nonvolatile nitrogenous compounds which were subsequently sorbed by the can lining. SIFT‐MS showed a 20‐fold increase in dimethyl sulfide concentration. Inductively coupled plasma (ICP‐MS) results showed fourfold and 16‐fold increases in iron and tin compounds, respectively, that migrated from the metal to the tomatoes as a result of acid and electrolyte interactions.

Standard Validation Protocol for Selected Ion Flow Tube Mass Spectrometry Methods Applied to Direct Headspace Analysis of Aqueous Volatile Organic Compounds.

Analysis of volatile organic compounds (VOCs) in water is conventionally conducted using gas chromatography (GC)-based methods, for which sample preparation demands are relatively high and throughput is relatively low due to the time taken to achieve chromatographic separation. Direct mass spectrometry (DMS) techniques such as selected ion flow tube mass spectrometry (SIFT-MS) have potential to analyze water headspace (HS) at high sensitivity with minimal sample preparation, eliminating preconcentration/purging and/or water management steps. However, the dearth of guidance for validation of DMS methods is an impediment to their adoption in routine analysis. This study applies and adapts an internationally recognized pharmaceutical industry guidance document for method validation to a prototypical SIFT-MS headspace analysis method for 17 toxic VOCs in water. The approach to validation is, however, applicable to any routine analysis conducted using SIFT-MS, and very likely to any methods developed using other DMS techniques. For the method developed and validated here, linearities (as measured by the linear regression coefficient, R2) were better than 0.990 for all compounds. Repeatability (measured using relative standard deviation, RSD) was less than 10% for all compounds. Similar method performance was observed for accuracy and recovery. The performance criteria achieved by this HS-SIFT-MS method suggest it has potential application in environmental and pharmaceutical routine analyses, perhaps as a rapid screening tool.

Selected ion flow tube mass spectrometry for targeted analysis of volatile organic compounds in human breath.

The analysis of volatile organic compounds (VOCs) within breath for noninvasive disease detection and monitoring is an emergent research field that has the potential to reshape current clinical practice. However, adoption of breath testing has been limited by a lack of standardization. This protocol provides a comprehensive workflow for online and offline breath analysis using selected ion flow tube mass spectrometry (SIFT-MS). Following the suggested protocol, 50 human breath samples can be analyzed and interpreted in <3 h. Key advantages of SIFT-MS are exploited, including the acquisition of real-time results and direct compound quantification without need for calibration curves. The protocol includes details of methods developed for targeted analysis of disease-specific VOCs, specifically short-chain fatty acids, aldehydes, phenols, alcohols and alkanes. A procedure to make custom breath collection bags is also described. This standardized protocol for VOC analysis using SIFT-MS is intended to provide a basis for wider application and the use of breath analysis in clinical studies.

Dairy product quality using screening of aroma compounds by selected ion flow tube‒mass spectrometry: A chemometric approach

Selected ion flow tube-mass spectrometry (SIFT-MS) can be used to analyse the concentration of volatile compounds in the headspace over food samples. Utilising chemometric classifiers, the concentration of aroma compounds detected by SIFT-MS was used to differentiate products. Nineteen compounds most useful in differentiating a range of dairy products were identified from the results of classification and selected for the development of preliminary threshold models to distinguish acceptable products from those containing off-aromas. Product differentiation was used to select the compounds for the threshold models, because sensory panel analysis rarely detects off-aromas in the products being examined. Threshold models for these compounds in the different products were developed using the 95% percentiles for the concentrations of these compounds that sensory panels found to be acceptable. These models have been used successfully during routine analysis to distinguish good products from marginal or off-aroma products, thereby lowering the demand on sensory panels.

MO143UTILITY OF SIFT-MS TO EVALUATE VOLATILE ORGANIC COMPOUNDS IN NEPHROPATHIC PATIENTS' BREATH

Abstract Background and Aims Breath analysis techniques allow detection and quantification of multiple analytes present in breath to the low parts per billion volume (ppbv) level. One such technique is selected ion flow tube–mass spectrometry (SIFT-MS), which can measure numerous volatile organic compounds (VOCs) in breath on-line and in real-time. This technique has already been used in an innovative manner to monitor infectious, inflammatory status and metabolic conditions. However, there is no evidence on its use in ambulatory patients with chronic kidney disease (CKD). End-stage-renal-disease patients are characterized by "uremic halitosis" caused by the accumulation of uremic toxins that are detectable in breath such as ammonia and amines. The aims of this study are identifying a possible correlation between the detected VOCs and the presence of CKD, moreover, exploring the range of VOCs levels in patients with different CKD stage. Method In the present study, a mobile Voice200ultra® SIFT-MS instrument was made available by the Agilent SRA Division. The SIFT-MS allowed to quantify the VOCs in CKD patients. The SIFT-MS uses a precise and controlled application of “soft” chemical ionization. We enrolled 50 CKD patients, divided into two subgroups according to the estimated glomerular filtration rate (eGFR): eGFR ≥30 mL/min/1.73m2 (A) and eGFR &amp;lt;30 mL/min/1.73m2 (B) compared to 18 healthy subjects (C). The anamnestic data and information about any comorbidities such as arterial hypertension, cardiovascular and metabolic diseases, were collected for each patient. In order to reduce the possible interferences in the exhaled composition induced by different lifestyles, all participants were instructed to perform hygienic procedures before the test execution. The exhaled was sampled through the use of a standard spirometry mouthpiece for single use, directly connected with the input probe to the MS detector of the instrument that was able to detect more than 30 VOCs. The processing of the sample was made through the direct use of an internal comparison library (Syft library). The SIFT-MS software instantly calculates the absolute concentration of the target compounds by interpolating mass-to-charge ratios, reaction rate coefficients and branching ratios. Results Among all the VOCs analyzed, the most significant results are observed for ammonia and isoprene. In particular, the ROC curve of ammonia highlighted statistically significant differences between the three subgroups respectively A vs C AUC=0,756 p=0,001; B vs C AUC=0,942 p&amp;lt;0,001; A vs B AUC=0,797 p&amp;lt;0,001 (Figure 1). Youden index J between subgroups B and C defines the best cut-off =0,8704 associated with the criterion ammonia concentration ≤4700 ppbv with sensitivity =94,44% and specificity = 92,59%. The ROC curve of isoprene showed statistically significant differences between the three subgroups respectively B vs C AUC=0,669 p=0,050; A vs B AUC=0,691 p=0,014 (Figure 2). These data allow us to define this a highly accurate test. The same significant results were observed also with Anova one-way test that highlighted an inversely correlation between the ammonia breath concentration and eGFR, and a direct correlation between isoprene and eGFR. Conclusion This preliminary data confirms the potential utility of SIFT-MS for the CKD diagnosis and the possible relation between the VOCs concentration and CKD stage. This exam could be a new, non-invasive, fast-performing diagnostic technique with real-time results useful for clinical management of CKD. The study was inserted in the projects: “MioMenù: nuova filiera dell’agro-industria e una cucina tracciata natura/benessere- Lazio Region” and “BioSynOL- Oil and Legumes: biodynamic and synergistic crops for naturally fortified foods and innovative products for health and sport – G.O.Tuscany Region”.

Toward ICP-SIFT mass spectrometry and atomic cation ligation as a probe of relativistic effects-A personal journey.

The ICP-SIFT mass spectrometer at York University, a derivative of flowing afterglow (FA) and selected-ion flow tube (SIFT) mass spectrometers, has provided a powerful technique to measure the chemistry and kinetics of atomic cation-molecule reactions. Here, I focus on periodic trends in the kinetics of ligation reactions of atomic ions with small molecules. I examine trends in ammonia ligation kinetics across the first two rows of the atomic transition metal cations and their correlation with ligand bond enthalpies and ligand field stabilization energies. Also explored are trends down Groups 1 and 2 in the kinetics of noncovalent electrostatic ligand bonding and the tendency for s electron solvation of the atomic alkaline-earth cations with ammonia. Finally, I briefly review trends observed with 12 different ligands in the ligation rate down the periodic table with Group 9-12 transition atomic metal cations. These trends provide a compelling probe for the presence of relativistic effects that influence the strengths of the metal-ion ligand bonds that are formed. There is a clear third-row rate enhancement with Ir+ , Pt+ , Au+ , and Hg+ , the extent of which depends on the nature of the ligand. This large set of kinetic data provides an unprecedented broad perspective of relativistic effects in ligand bonding. With CS2 as a ligand, the third-row relativistic effect is apparent in the formation of both the first and the second ligand bond with the Groups 10 and 11 atomic cations as predicted by our quantum chemical calculations of ligation energies.

Application of Routine Analysis Procedures to a Direct Mass Spectrometry Technique: Selected Ion Flow Tube Mass Spectrometry (SIFT-MS)

In recent years the environmental and human health impacts of volatile organic compounds (VOCs) have become more apparent, resulting in increased analysis demand. The gold-standard chromatographic techniques continue to be employed for most laboratory analyses. However, they have made only modest gains in productivity over the years, and these gains are primarily due to automated sample preparation and injection. Alternatively, significant productivity gains for VOC analysis through faster sample analysis and reduced instrument maintenance could be achieved by adopting direct mass spectrometry techniques such as selected ion flow tube mass spectrometry (SIFT-MS). This article demonstrates that routine analysis techniques such as quality control checks, method validation, the method of standard additions, and internal standards are readily applied to SIFT-MS, simplifying adoption of the technique. In addition, workflows for analysis of chromatographically challenging species are simplified by using SIFT-MS. Sample throughputs are increased two- to 25-fold depending on the analytical procedure.

Old School Techniques with Modern Capabilities: Kinetics Determination of Dynamical Information Such as Barriers, Multiple Entrance Channel Complexes, Product States, Spin Crossings, and Size Effects in Metallic Ion-Molecule Reactions.

We show how the powerful combination of temperature-dependent kinetics coupled with detailed statistical modeling can be used to derive dynamical information about transition state barrier heights, the importance of multiple entrance channel complexes, crossings between spin surfaces, energetics, product states, and other information for metal-ion reactions. The methods are not new, but with improved computers, ion sources, ion transport, and better detection techniques, the ability to derive such parameters from the combination of methods has improved greatly. Temperature-dependent kinetics is very sensitive to the above list of parameters because the energy is varied in a controlled way that can be easily modeled. The present measurements, performed in our variable-ion source temperature-adjustable selected-ion flow tube (VISTA-SIFT), have been enabled by advances in ion transport and injection improvements so that dim sources can be used. Replacing the quadrupole mass spectrometer detector with a time-of-flight mass spectrometer solved additional problems. Quantum chemical calculations have improved greatly and provide details about the surfaces, as well as frequencies, to use as starting points for the statistical modeling. For ion-molecule reactions, incorporation of both energy and angular momentum effects are important and we have developed an in-house computer program, based on the work of Juergen Troe, to rapidly compare statistical modeling predictions to the experimental data. As we show, modeling the kinetics data can often determine the most important parameters controlling the reactivity and deriving them is much simpler and usually more accurate than detailed ab initio calculations or dynamical modeling. Additionally, we show that even without statistical modeling, temperature-dependent rate constants as a function of metal anion cluster size can be used to show that such species react by the same mechanism as surfaces. In this review, we discuss reactions of metallic atomic ions, small metal oxide ions, mixed metal oxide ions, and a series of metallic anionic cluster reactions with small molecules such as CO, O2, CO2, N2O, CH4, and several other species. Particular attention was paid to reactions involving bond activation pertinent to catalysis.

Cross Platform Analysis of Volatile Organic Compounds Using Selected Ion Flow Tube and Proton-Transfer-Reaction Mass Spectrometry.

Volatile breath metabolites serve as potential disease biomarkers. Online mass spectrometry (MS) presents real-time quantification of breath volatile organic compounds (VOCs). The study aims to assess the relationship between two online analytical mass spectrometry techniques in the quantification of target breath metabolites: selected ion flow tube mass spectrometry (SIFT-MS) and proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). The two following techniques were employed: (i) direct injection with bag sampling using SIFT-MS and PTR-ToF-MS and (ii) direct injection and thermal desorption (TD) tube comparison using PTR-ToF-MS. The concentration of abundant breath metabolites, acetone and isoprene, demonstrated a strong positive linear correlation between both mass spectrometry techniques (r = 0.97, r = 0.89, respectively; p < 0.001) and between direct injection and TD tube (r = 0.97, r = 0.92, respectively; p < 0.001) breath sampling techniques. This was reflected for the majority of short chain fatty acids and alcohols tested (r > 0.80, p < 0.001). Analyte concentrations were notably higher with the direct injection of a sampling bag compared to the TD method. All metabolites produced a high degree of agreement in the detection range of VOCs between SIFT-MS and PTR-ToF-MS, with the majority of compounds falling within 95% of the limits of agreement with Bland-Altman analysis. The cross platform analysis of exhaled breath demonstrates strong positive correlation coefficients, linear regression, and agreement in target metabolite detection rates between both breath sampling techniques. The study demonstrates the transferability of using data outputs between SIFT-MS and PTR-ToF-MS. It supports the implementation of a TD platform in multi-site studies for breath biomarker research in order to facilitate sample transport between clinics and the laboratory.