Pressure Ionization Research Articles

Liquid chromatography coupled to Venturi easy ambient sonic spray ionization mass spectrometry

Venturi easy ambient sonic spray ionization (V-EASI) is a soft ambient ionization (AI) source that has the advantages of being suitable to the analysis of samples in solution (differently from the majority of AI sources), performing self-pumping, voltage- and heat-free ionization, and requiring minimum or no sample preparation. Since this ionization technique has not been fully explored, the present study provides a proof of principle of the coupling of liquid chromatography to mass spectrometry (LC-MS) using V-EASI as the interface. In order to test the performance of the developed LC-V-EASI-MS system, a quantification method for bixin, a natural dye from annatto (Bixa Orellana L.), which is known to be sensitive to the high voltage applied for electrospray ionization mass spectrometry (ESI-MS) analysis, was validated according to FDA criteria and tested in real samples. The analytical method was successfully applied and met the validation criteria, providing a detectability 10 times better than methods already reported to the quantification of bixin and no matrix effect was observed. Therefore, this proof of principle contributes to the continuous development of AI sources that represents the last great technological advance in MS towards becoming a miniaturized technique able to analyze samples closer to their actual state.

In-Line Dopant Generation for Atmospheric Pressure Ionization Mass Spectrometry.

A concentric trace gas permeation tube that diffuses chemical reagents to a central carrier gas stream is used to drive chemical reaction pathways and influence gas-phase chemistry for a variety of atmospheric pressure ionization sources for mass spectrometry. Tunable permeation through the reservoir-jacketed polymer membrane is triggered by the heated gas moving through the tube, evaporating the dopant into a sheath dry gas or into a sample stream in room air without diluting the analyte concentration. The permeator is used to add dopants to an electrospray plume for analyte ion charge reduction and to perform hydrogen-deuterium exchange on biomolecules in different spray conditions. Dopants are also added to atmospheric pressure chemical ionization to favor the ionization of select components of diesel fuel. Atmospheric pressure photoionization is performed with the permeation tube in line with tubing transporting sample headspace to an enclosed discharge lamp. Toluene dopant from the permeator increases the proton transfer and charge exchange signal from clove oil and mothballs many times without exposing the laboratory to reagent fumes. Water permeation is also used to humidify the sample gas stream.

Assessment of the reliability of ionization current measurement in estimating peak pressure angle in a spark ignition engine

Ionization current measured at the spark plug during combustion in spark ignition engines has often been proposed to determine the crank-angle at combustion pressure peak, namely the peak pressure angle, for the purpose of regulating spark timing to attain maximum brake torque (MBT). The proposal is based on the assumption that agreement exists between peak pressure angle and the angular position of the ionization current second peak, although no one has ever proved it by an appropriate statistical analysis. The aim of this work, for the first time and by rigorous statistical methods, is to prove the agreement between Peak Pressure Angle and Ionization Current Second Peak Angle (ICSPA), without which a MBT control via ICSPA would be ineffective. Our experimental database consisted of about 9000 pairs of Peak Pressure Angle and Ionization Current Second Peak Angle values corresponding to 90 different operating conditions of a spark ignition engine. A two-sample comparison was first carried out between mean values of Peak Pressure Angle and Ionization Current Second Peak Angle, which showed a statistically significant difference between them. Then Bland-Altman analysis (Lancet, 1986), widely known and used for checking agreement between two different measurement methods, was conducted. It demonstrated that under almost all the experimental operating conditions, there was no agreement between the Ionization Current Second Peak Angle and the Peak Pressure Angle.

Quality control measures of thermoluminescent dosimetry system used in environmental radiation monitoring

Objective To discuss the quality control measures of the thermoluminescent dosimetry system and to verify its propriety of when used in environmental radiation monitoring. Methods The quality control measures included the stability test, the dispersibility screening and the uncertainty evaluation of measurement results of the TLD reader and TLD detector, in addition, the environmental radiation accumulated dose monitoring results obtained by the high pressure ionization chamber were compared with those by the thermoluminescent dosimetry system. Results The variation range of TLD reader’s light source coefficient is within 0.070~0.073 during the preheating and measuring process, which meets the requirements of stability; The χ 2 value of the TLD detector is 2.088, which obeys the normal distribution; The thermoluminescent dosimetry system’s nonlinear response, coefficient of variation and energy response meet the measurement requirements; There is a deviation of −6.58% the largest between the cumulative dose obtained by TLD and the high pressure ionization chamber. Conclusion The quality control measures discussed in this paper can be used as a reference for similar thermoluminescent dosimetry system. Our system has passed all the tests and can meet the environmental radiation cumulative dose monitoring requirements. 摘要： 目的 探讨热释光测量系统的质量控制方法, 验证热释光测量系统能否准确有效的用于环境辐射水平监测。 方法 采取的环境辐射监测用热释光测量系统质量控制方法包括热释光测量系统的稳定性检验、热释光探测器的分 散性筛选、测量结果不确定度评定, 并与高气压电离室测量方法进行对比。 结果 读出器预热及测读过程中光源系数 变化范围在 0.070~0.073, 稳定性符合使用要求; 热释光探测器的 χ 2 值为 2.088, 服从正态分布;热释光测量系统满足 非线性响应、变异系数和能量响应的计量要求; 热释光累积剂量测量结果与高气压电离室相比偏差最大 −6.58%。 结论 本实验室采取的质控措施可作为同类热释光测量系统的质控措施的参考;本实验室的热释光测量系统通过了 各项检验, 满足环境辐射累积剂量监测的使用要求。

A Tapered Capillary-Based Contactless Atmospheric Pressure Ionization Mass Spectrometry for On-Line Preconcentration and Separation of Small Organics

Capillary electrophoresis (CE) is an effective technique for the separation of different analytes. Moreover, online preconcentration of trace analytes in the capillary for CE analysis has been demonstrated. CE and capillary electrochromatography (CEC) are suitable for the separation of analytes with similar polarities. Given that CE and CEC are only used to separate small-volume samples, sensitive mass spectrometry (MS) is a suitable detection tool for CE and CEC. Contactless atmospheric pressure ionization (C-API) is a continuous flow ion source that only uses a short capillary as the ionization emitter operated at atmospheric pressure for MS analysis. In this study, we demonstrated the feasibility of hyphenating CE/CEC with C-API-MS by using a short and tapered capillary as the interface. The short capillary (a few centimeters) can function as the separation/preconcentration tube and the ionization emitter. This hyphenated technique can be used to analyze small organics within a few minutes. The suitability of using the hyphenated technique for online preconcentration, separation, and quantitative analysis for small organics is demonstrated in this study.

Study of atmospheric pressure chemical ionization of phthalates in air by ion mobility spectrometry/mass spectrometry.

Phthalates are widely used in consumer products in the chemical industries. Due to their abundance in the milieu, their potentially harmful effect on the environment, human and animal health there is a need for sensitive and fast methods for their detection. Positive polarity Corona Discharge Atmospheric Pressure Chemical Ionization (CD-APCI) in the air was applied for ionization of phthalates. The ionization method for the phthalates was studied by atmospheric pressure Ion Mobility Spectrometry (IMS) and hybrid IMS/orthogonal acceleration Time-of-Flight Mass spectrometry (IMS-oaTOF-MS). CD-APCI IMS and MS spectra of selected phthalates (dimethyl phthalate, diethyl phthalate, diethyl isophthalate, diethyl terephthalate, dipropyl phthalate, diisopropyl phthalate, dibutyl phthalate, diisobutyl phthalate, and dibutyl terephthalate) were recorded. In the case of the ortho- and "iso"-isomers exclusively the protonated molecular ions [M+H]+ were detected. In the case of the para- and meta-isomers and regioisomers, APCI resulted in the appearance of hydrated protonated molecular ions [M + H]+ ·(H2 O)0,1,2 . The ion mobilities, collision cross-sections of these ions in air, as well as the limits of detection (LODs) for the phthalate vapors, were determined. In the case of isomeric phthalates, we have demonstrated the potential of the IMS technique for their separation. The results show that CD-APCI in combination with IMS and IMS-oaTOF-MS is a suitable method for the fast and sensitive detection of phthalates with the potential to separate some isomers.

Observation of charged droplets from electrospray ionization (ESI) plumes in API mass spectrometers

Electrospray ionization (ESI) generates bare analyte ions from charged droplets, which result from spraying a liquid in a strong electric field. Experimental observations available in the literature suggest that at least a significant fraction of the initially generated droplets remain large, have long lifetimes, and can thus aspirate into the inlet system of an atmospheric pressure ionization mass spectrometer (API-MS). We report on the observation of fragment signatures from charged droplets penetrating deeply the vacuum stages of three commercial mass spectrometer systems with largely different ion source and spray configurations. Charged droplets can pass through the ion source and pressure reduction stages and even into the mass analyzer region. Since droplet signatures were found in all investigated instruments, the incorporation of charged droplets is considered a general phenomenon occurring with common spray conditions in ESI sources.

Acoustic Mist Ionization Mass Spectrometry for Ultrahigh-Throughput Metabolomics Screening.

Incorporating safety data early in the drug discovery pipeline is key to reducing costly lead candidate failures. For a single drug development project, we estimate that several thousand samples per day require screening (<10 s per acquisition). While chromatography-based metabolomics has proven value at predicting toxicity from metabolic biomarker profiles, it lacks sufficiently high sample throughput. Acoustic mist ionization mass spectrometry (AMI–MS) is an atmospheric pressure ionization approach that can measure metabolites directly from 384-well plates with unparalleled speed. We sought to implement a signal processing and data analysis workflow to produce high-quality AMI–MS metabolomics data and to demonstrate its application to drug safety screening. An existing direct infusion mass spectrometry workflow was adapted, extended, optimized, and tested, utilizing three AMI–MS data sets acquired from technical and biological replicates of metabolite standards and HepG2 cell lysates and a toxicity study. Driven by criteria to minimize variance and maximize feature counts, an algorithm to extract the pulsed scan data was designed; parameters for signal-to-noise-ratio, replicate filter, sample filter, missing value filter, and RSD filter were all optimized; normalization and batch correction strategies were adapted; and cell phenotype filtering was implemented to exclude high cytotoxicity samples. The workflow was demonstrated using a highly replicated HepG2 toxicity data set, comprising 2772 samples from exposures to 16 drugs across 9 concentrations and generated in under 5 h, revealing metabolic phenotypes and individual metabolite changes that characterize specific modes of action. This AMI–MS workflow opens the door to ultrahigh-throughput metabolomics screening, increasing the rate of sample analysis by approximately 2 orders of magnitude.

Pattern-Type Separation of Triacylglycerols by Silver Thiolate×Non-Aqueous Reversed Phase Comprehensive Liquid Chromatography

Triacylglycerols (TAGs), as the main components of edible oils and animal fats, are responsible for the nutritional value, organoleptic features and technological properties of foods; each lipid matrix shows a unique TAG profile which can serve as fingerprint to ensure the quality and authenticity of food products. The high complexity of many foodstuffs often makes untargeted elucidation of TAG components a challenging task; thus, more efficient separation techniques may be mandatory. In this research, the TAG profile of a borage (Borago officinalis) seed oil was obtained by two-dimensional comprehensive liquid chromatography (LC×LC), by the coupling of silver thiolate and octadecylsilica monodisperse materials. A total 94 TAG compounds were identified by ion trap-time of flight detection, using atmospheric pressure ionization, with the degree of unsaturation varying from 0 to 9, and partition values ranging from 36 to 56. The group-type separation afforded by this analytical approach may be useful to quickly fingerprint TAG components of oil samples.

Fluid Dynamics of the Open Port Interface for High-Speed Nanoliter Volume Sampling Mass Spectrometry.

The open port interface (OPI) coupled to an atmospheric pressure ion source is used to capture, dilute, focus, and transport nanoliter volume sample droplets for high-speed mass spectrometric analysis. For typical applications, the system has been optimized to achieve 1 Hz nanoliter volume sample transfer rates while simultaneously diluting the sample >1000-fold to minimize sample matrix-induced ionization suppression. Geometric, flow, and dispensing alterations to the system presented here demonstrate that sample transfer rates for the OPI of at least 15 Hz are possible. The fluid dynamic processes that enable sampling rates of 1 Hz and greater are examined in detail by correlating computational fluid dynamics simulations, analytic calculations, experimental data, photographic footage, and reference to the fluid dynamics literature. The resulting models and experimental results provide the rationale underlying the design and tuning of the system as well as information for developing optimized analytical methods. In combination with acoustic droplet dispensing, referred to as acoustic ejection mass spectrometry (AEMS), this system can be considered to be a special case of flow injection analysis with unique features that control the peak width, symmetry, and segregation of the samples transported in a fluid while simultaneously enabling their mixing and dilution with carrier fluids. In addition, conditions are established to prevent direct contact of the sample with a surface enabling, in combination with a contact-free dispenser like acoustic ejection, a dramatic reduction in sample-to-sample carry-over.

Space charge compensation in air by counterion flow in 3D printed electrode structure

Electrospray ionization is commonly employed in modern mass spectrometry experiments for applications ranging from proteomics to environmental science and for fundamental studies of the chemical reactivity of ions. Despite the ubiquity of electrospray ionization, the total ion currents achieved using the technique remain relatively poor. While there are significant losses within the atmospheric pressure interface of the mass spectrometer (MS), many ions are lost due to space charge repulsion before ions and charged microdroplets enter the instrument. Space charge effects also limit the extent to which multiplexing of electrosprays can be used to increase ion currents. In this work, a flow of oppositely charged ions produced by atmospheric pressure chemical ionization (APCI) is employed to mitigate space charge effects in an analyte ion beam produced by nanoelectrospray ionization (nESI) as it is passed through an atmospheric pressure ion guide outside of a mass spectrometer. A decrease in the nESI beam width together with an increase in peak intensity is observed using an ion charge coupled detector in the presence of a counterflow of ions of the opposite charge. This result indicates that focusing occurs in the ion guide. Measurements of the space charge compensated ion beam using an Agilent Ultivo triple quadrupole mass spectrometer are correlated with changes in ion focusing, indicating that space charge compensation occurring before the ion beam enters the mass spectrometer can increase detected ion currents.

Ion density of positive and negative ions at ambient pressure in air at 12-136mm from 4.9 kV soft x-ray source.

The abundance of ions is an essential parameter for ion mobility and mass spectrometry instrument design and for the control or optimization of chemical reactions with reactant ions. This information also advances the study of atmospheric pressure ion kinetics under continuous ionization, which has a role in developing trace level chemical analyzers. In this study, an ionization chamber is described to measure the abundance of ions produced by a 4.9 keV, model L12535, soft x-ray source from Hamamatsu Corporation. Ions of positive and negative polarity were measured independently in an 8 × 30mm2 cross section at distances of 12-136mm at ambient air from an uncollimated beam. Ions were collected using electric fields and 16 sets of plates. The ion current decreased exponentially with distance from the source, and the calculated ion concentration varied between 1.0 × 108 and 3.8 × 105 ionscm-3 on plates. A 2D-COMSOL model including losses by recombination and diffusion was favorably matched to changes in ion current intensity in the ionization chamber. Although the ionization chamber was built to characterize a commercial ion source, the design may be considered generally applicable to other x-ray sources.

Determination of banned dyes in red spices by ultra-high-performance liquid chromatography-atmospheric pressure ionization-tandem mass spectrometry

This paper reports the development of an ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC‒MS/MS) method to determine eight banned dyes (Sudan I-IV, Sudan Orange, Sudan Red 7B, Para Red, Rhodamine B) in turmeric, curry, and chili products. For this purpose, the feasibility of electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) for the ionization of these compounds was evaluated. The tandem mass spectrometry (MS/MS) fragmentation of all targeted compounds was studied and both multistage mass spectrometry and high-resolution mass spectrometry were used to establish the fragmentation pathways and identify common fragmentation behaviors. Among the most significant ions, the most characteristic and abundant product ions observed on the triple quadrupole were selected to propose a selective and sensitive UHPLC‒MS/MS method (multiple reaction monitoring mode, MRM) of these target compounds in spices samples after a quick and easy extraction with acetonitrile. Matrix effect (ME) studies carried out in the three atmospheric pressure ionization sources have demonstrated that APCI showed the best performance with ME values ranging from 2 to 25%. Furthermore, the estimated quality parameters indicated the good performance of the proposed method, providing low method limits of detection (MLODs) (1–48 μg kg−1), good intra-day precision (RSD % < 15%), and accurate quantitation (relative error % < 15%). Finally, the applicability of the developed method was demonstrated by the analysis of turmeric, curry, and chili products. In total, 36 diverse samples coming from different countries were analyzed and although none of these compounds were detected above the MLODs, the analysis of spiked samples showed that the method was able to detect this family of compounds at low μg kg−1.

Rapid and direct detection of artificially aged papers employing easy ambient sonic-spray ionization mass spectrometry.

The effort to make fake documents look real leads to the use of crickets and beverages to produce artificially aged papers, as land titles, based on yellowing caused by the use of these methods. An old practice in Brazil, called "cricketing", has led to the misappropriation of Brazilian land using these documents. We propose a rapid, simple, instantaneous and non-destructive method to identify artificially aged papers by easy ambient sonic-spray ionization mass spectrometry (EASI-MS) analysis. Three typical aging procedures were used to obtain artificially aged papers using coffee, cola drink, and crickets, with the papers being analyzed by EASI-MS. Multivariate statistical analyses were performed on the data to find the sample groups and to study the most relevant ions of each ageing procedure. High-resolution MS (HRMS) was used to obtain the exact masses and attribute formulae to relevant ions present in the samples. The combination of EASI-MS and multivariate statistical analyses allowed us to identify the most relevant ions to classify the adulteration of documents and HRMS identified most of these relevant ions. TMS fingerprinting in combination with multivariate analysis also demonstrated that this approach can qualitatively differentiate all the examined paper samples. We developed a cheap, fast and easy method that can help to elucidate counterfeit documents that have been artificially aged, helping to identify chemical additives and one that can be used in forensic laboratories.

Accelerated Oxidation of Organic Sulfides by Microdroplet Chemistry.

We report the rapid oxidation of organic sulfides to sulfoxides by means of microdroplet chemistry at room temperature using a spray solution containing an organic sulfide dissolved in water/methanol, dilute (11%-14%) sodium hypochlorite (NaClO), and 5% chloroauric acid (HAuCl4). Ultrasonic nebulization, easy ambient sonic-spray ionization, or electrosonic spray ionization serves as the microdroplet source. High-resolution mass spectrometry was used as an online detector, and nuclear magnetic resonance was used as an offline detector. We found that the sulfoxide yields vary between 66 and 95%, the highest rate of product formation is 195 mg/min for benzyl phenyl sulfoxide, and the time required is a few minutes, which is much less than that required for the conventional means of achieving this chemical transformation. We also applied this microdroplet method to protein fingerprinting. We found that protein sequences containing methionine can be quickly oxidized, providing useful information for protein structure determinations.

Impact of Ambient Vapors Present in an Electrospray Ionization Source on Gas-Phase Ion Structures.

According to current consensus, structures of protomeric (or deprotomeric) tautomers of gaseous ions generated by electrospray ionization depend primarily on the nature of the spray solvent. To probe the effect of the spray solvent on protonation, 4-aminobenzoic acid (PABA) has often been selected as the model compound. It is widely accepted that the protonation in the gas phase takes place primarily on the carbonyl oxygen atom when the sample is sprayed in methanol and on the nitrogen atom when acetonitrile is used as the spray solvent. Although this observation is valid, our current results indicate that the determination of the predominant protomer in the gas phase by the spray solvent is an indirect effect moderated by the solvent vapor molecules present in the ambient ion source. To investigate real-time changes in protomer distributions due to solvents, we used ion-mobility mass spectrometry (IM-MS). Initially, when a PABA solution in methanol was electrosprayed, the ion-mobility arrival-time profile recorded showed essentially one peak for the O-protomer. However, when acetonitrile or acetone vapors were introduced to the ambient-pressure ion source via the flowing desolvation gas, the intensity of the O-protomer peak diminished rapidly, and the N-protomer signal became dominant. The moment the acetonitrile (or acetone) vapors were removed from the ion source, the protomer-distribution signals began gradually reverting back to their original intensities. Furthermore, when PABA samples in methanol and acetonitrile were electrosprayed separately via a dual-sprayer setup, which allowed for the selective blocking of the gaseous ion-generation cascade of charged droplets from either sprayer, the predominant signal corresponded only to the N-protomer, irrespective of the position of the mechanical barrier. Because the mechanical barrier prevents only the gaseous ion formation, but not the physical access of solvent vapors to the ion source, it is evident that the solvent vapor that engulfs the ion source is the governing factor that decides the protomer distribution, not the nature of the spray solvent. Noticeably, acetonitrile wields a stronger effect on the manifested protomer distribution than many other solvents, including methanol, water, hexanes, and toluene. Apparently, the so-called "memory" of the solution-phase structures and the phenomenon described as "kinetic trapping" are both due to indirect effects caused by the solvent vapor engulfing the atmospheric-pressure ion source. Moreover, the so-called "memory" effect can either be "saved" or "erased" by exposing the initially formed gaseous ions to different solvent vapors from an alternative source.

Effects of liquid–liquid phase separation and relative humidity on the heterogeneous OH oxidation of inorganic–organic aerosols: insights from methylglutaric acid and ammonium sulfate particles

Abstract. Organic compounds residing near the surface of atmospheric aerosol particles are exposed to chemical reactions initiated by gas-phase oxidants, such as hydroxyl (OH) radicals. Aqueous droplets composed of inorganic salts and organic compounds can undergo phase separation into two liquid phases, depending on aerosol composition and relative humidity (RH). Such phase behavior can govern the surface characteristics and morphology of the aerosols, which in turn affect the heterogeneous reactivity of organic compounds toward gas-phase oxidants. In this work, we used an aerosol flow tube reactor coupled with an atmospheric pressure ionization source (direct analysis in real time) and a high-resolution mass spectrometer to investigate how phase separation in model aqueous droplets containing an inorganic salt (ammonium sulfate, AS) and an organic acid (3-methylglutaric acid, 3-MGA) with an organic-to-inorganic dry mass ratio (OIR) of 1 alters the heterogeneous OH reactivity. At high RH, 3-MGA/AS aerosols were aqueous droplets with a single liquid phase. When the RH decreased, aqueous 3-MGA/AS droplets underwent phase separation at ∼75 % RH. Once the droplets were phase-separated, they exhibited either a core–shell, partially engulfed or a transition from core–shell to partially engulfed structure, with an organic-rich outer phase and an inorganic-rich inner phase. The kinetics, quantified by an effective heterogenous OH rate constant, was found to increase gradually from 1.01±0.02×10-12 to 1.73±0.02×10-12 cm3 molec.−1 s−1 when the RH decreased from 88 % to 55 %. The heterogeneous reactivity of phase-separated droplets is slightly higher than that of aqueous droplets with a single liquid phase. This could be explained by the finding that when the RH decreases, higher concentrations of organic molecules (i.e., 3-MGA) are present at or near the droplet surface, which are more readily exposed to OH oxidation, as demonstrated by phase separation measurements and model simulations. This could increase the reactive collision probability between 3-MGA molecules and OH radicals dissolved near the droplet surface and secondary chain reactions. Even for phase-separated droplets with a fully established core–shell structure, the diffusion rate of organic molecules across the organic-rich outer shell is predicted to be fast in this system. Thus, the overall rate of reactions is likely governed by the surface concentration of 3-MGA rather than a diffusion limitation. Overall, understanding the aerosol phase state (single liquid phase versus two separate liquid phases) is essential to better probe the heterogenous reactivity under different aerosol chemical composition and environmental conditions (e.g., RH).

Long-term measurement of sub-3 nm particles and their precursor gases in the boreal forest

Abstract. The knowledge of the dynamics of sub-3 nm particles in the atmosphere is crucial for our understanding of the first steps of atmospheric new particle formation. Therefore, accurate and stable long-term measurements of the smallest atmospheric particles are needed. In this study, we analyzed over 5 years of particle concentrations in size classes 1.1–1.7 and 1.7–2.5 nm obtained with the particle size magnifier (PSM) and 3 years of precursor vapor concentrations measured with the chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-ToF) at the SMEAR II station in Hyytiälä, Finland. The results show that there are significant seasonal differences in median concentrations of sub-3 nm particles, but the two size classes behave partly differently. The 1.1–1.7 nm particle concentrations are highest in summer, while the 1.7–2.5 nm particle concentrations are highest in springtime. The 1.7–2.5 nm particles exhibit a daytime maximum in all seasons, while the 1.1–1.7 nm particles have an additional evening maximum during spring and summer. Aerosol precursor vapors have notable diurnal and seasonal differences as well. Sulfuric acid and highly oxygenated organic molecule (HOM) monomer concentrations have clear daytime maxima, while HOM dimers have their maxima during the night. HOM concentrations for both monomers and dimers are the highest during summer and the lowest during winter following the biogenic activity in the surrounding forest. Sulfuric acid concentrations are the highest during spring and summer, with autumn and winter concentrations being 2 to 3 times lower. A correlation analysis between the sub-3 nm concentrations and aerosol precursor vapor concentrations indicates that both HOMs (particularly their dimers) and sulfuric acid play a significant role in new particle formation in the boreal forest. Our analysis also suggests that there might be seasonal differences in new particle formation pathways that need to be investigated further.

Determination of selected water-soluble vitamins (thiamine, riboflavin, nicotinamide and pyridoxine) from a food matrix using hydrophilic interaction liquid chromatography coupled with mass spectroscopy

Water-soluble vitamins are essential dietary components with a multitude of important functions that require quantification from food sources to characterise the nutritional status of food. In this study, we have developed a hydrophilic interaction chromatography (HILIC) based method coupled to single-quadrupole mass spectrometry (MS) for the analysis of selected water-soluble vitamins. Due to their involvement in energy release from macronutrients, the quantification of thiamine (B1), riboflavin (B2), nicotinamide (B3) and pyridoxine (B6) offers significant value in food analysis.A commercially available vegetable soup was selected as the food matrix for this study and utilised to develop an efficient extraction procedure for the vitamins of interest. Vitamins were extracted using meta-phosphoric acid coupled with a reducing agent, DL-dithiothreitol (DTT) to produce the parent compound. The extracted vitamins were then analysed using an LC-MS system with electrospray – atmospheric pressure ionization (ES-API) source, operated in positive single ion monitoring (SIM) mode. The MS provided good linearity within the investigated range from 5 to 400 ng/mL with coefficient of determination (r2) ranging from 0.98 to 0.99. Retention times (0.65–9.04 min) were reproducible and no coelution between vitamins was observed. Limit of detection (LOD) varied from 2.4 to 9.0 ng/mL and limit of quantification (LOQ) was from 8 to 30 ng/mL, comparable to previously published studies. The extraction method provided good intra-day (%CV 1.56–6.56) and inter-day precision (%CV 8.07–10.97). Standard injections were used as part of quality control measures and provided excellent reproducibility (%CV 0.9–3.4). The overall runtime of this method was 19 min, including column reconditioning. Using this method, the quantity of thiamine (67 ± 7 ng/g), riboflavin (423 ± 39 ng/g), nicotinamide (856 ± 77 ng/g) and pyridoxine (133 ± 11 ng/g) was determined from a complex food matrix.In conclusion, we have developed a rapid and reliable, HILIC-single quad MS method utilising SIM for the low-level quantification of four B vitamins in a vegetable soup matrix in under 20 min. This method has shown excellent linearity, intra- and inter-day reproducibility and is directly applicable to other plant-based food matrices.

Super Transition Arrays: A Tool for Studying Spectral Properties of Hot Plasmas

For the theoretical study of X and extreme-UV spectra of ions in plasmas, quantum mechanics brings more detailed results than statistical physics. However, it is impossible to handle individually the billions of levels that must be taken into account in order to properly describe hot plasmas. Such levels can be gathered into electronic configurations or superconfigurations (groups of configurations) and the corresponding calculations rely on appropriate statistical methods, for local or non-local thermodynamic equilibrium plasmas. In this article we present the basic principles of the Super-Transition-Array approach as well as its practical implementation. During the last decades, calculations performed with the SCO code (Superconfiguration Code for Opacity) have been compared to opacity measurements. The code includes static screening of ions by plasma and is well suited for studying plasma density effects (for example pressure ionization) on opacity and equation of state. The recently developed SCO-RCG code (Superconfiguration Code for Opacity combined with Robert Cowan’s “G” subroutine) combines statistical methods from SCO and fine-structure (detailed-level-accounting) calculations using subroutine RCG from Cowan’s code. SCO-RCG enables us to obtain very detailed spectra and to significantly improve the interpretation of experimental spectra. The Super-Transition-Array formalism is still the cornerstone of several opacity codes, and new ideas are emerging, such as the Configurationally Resolved-Super-Transition-Array approach or the extension of the Partially Resolved-Transition-Array concept to the superconfiguration method.