Electrospray Ionization Orbitrap Mass Spectrometry Research Articles

Selective Profiling of Carboxylic Acid in Crude Oil by Halogen Labeling Combined with Liquid Chromatography and High-Resolution Mass Spectrometry.

Carboxylic acids are a small but essential compound class within petroleum chemistry, influencing crude oil behaviors in production and processing and causing environmental impacts. Detailed structural information is fundamental to understanding their influence on petroleum characteristics. However, characterizing acids in crude oil remains challenging due to matrix effects, structural diversity, and low abundance. In this work, we present a new methodology for profiling carboxylic acids by liquid-liquid extraction and selective derivatization using 4-bromo-N-methylbenzylamine (4-BNMA) followed by liquid chromatography and electrospray ionization Orbitrap mass spectrometry (LC-ESI-Orbitrap MS). The fragmentation of 4-BNMA derivatives produces a unique product ion pair, m/z 169/171, enabling the identification of chromatographic fractions containing carboxylic acids. The mass spectra of the corresponding fractions are extracted, and the acids are further computationally isolated based on the isotopic pattern. The method was optimized and validated using acid standards and systematic experimental designs, assuring robustness and sensitivity for nontarget screening purposes. This method detected up to 380 carboxylic acids in six Danish North Sea crude oils, with up to two carboxyl and other heteroatom functionalities (NSO). The results indicated that the most populated species are fatty acids (double bond equivalent (DBE) = 1) and small aromatic acids (DBE = 2-6). The predominance and diversities of compound classes in different samples are consistent with their corresponding bulk properties. Polyfunctional acids (Ox, NxOx, and SxOx) were observed due to exposure to oxidation and biodegradation. Also, the approach's applicability benefits high-resolution MS analysis by simplifying data processing for crude oil and potentially other high-organic and aqueous samples.

Comprehensive Identification of the Chemical Substances in Effective Component Groups of Polygalae Radix Based on Targeted Tandem Mass Spectrometry Analysis Strategy

ABSTRACTPolygalae Radix is a commonly used traditional Chinese medicine with multiple pharmacological activities. Modern research have revealed that saponins, xanthones, and oligosaccharide esters are its effective component groups. However, up to date the chemical substances in these effective component groups are still unclear, which has become a fundamental scientific issue needing to be addressed. In our study, an analysis strategy based on targeted tandem mass spectrometry (MS/MS) analysis was proposed to comprehensively identify the chemical substances in effective component groups. First, the extract of the Polygalae Radix was detected by ultra‐performance liquid chromatography coupled with electrospray ionization–orbitrap mass spectrometry in a full MS scan mode to minimize the losses of signals; second, the precursor ions of all compounds were extracted from the obtained full MS scan data using Compound Discoverer software; third, the interested precursor ions were locked based on their molecular features and constructed in a precursor ion list; finally, each precursor ion in the list was subjected to targeted MS/MS analysis for structure characterization. Using our analysis strategy, a total of 565 components were successfully identified.

Differential Extraction and Preliminary Identification of Polyphenols from Ugni candollei (White Murta) Berries.

Ugni candollei, commonly known as white murta, is a native Chilean berry with a polyphenol composition that has been underexplored. This study aimed to establish a comprehensive profile of white murta polyphenols using ultra-performance liquid chromatography electrospray ionization Orbitrap mass spectrometry (UPLC-ESI-ORBITRAP MS). Additionally, it compared the efficacy of conventional extraction methods with emerging techniques such as deep eutectic solvent (DES) extraction and hot pressurized water extraction (HPWE). The analysis tentatively identified 107 phenolic compounds (84 of them reported for the first time for this cultivar), including 25 phenolic acids, 37 anthocyanins, and 45 flavonoids. Among the prominent and previously unreported polyphenols are ellagic acid acetyl-xyloside, 3-p-coumaroylquinic acid, cyanidin 3-O-(6'-caffeoyl-glucoside, and phloretin 2'-O-xylosyl-glucoside. The study found HPWE to be a promising alternative to traditional extraction of hydroxybenzoic acids, while DES extraction was less effective across all categories. The findings reveal that white murta possesses diverse phenolic compounds, potentially linked to various biological activities.

A guide to precise measurements of isotope abundance by ESI-Orbitrap MS.

Stable isotopes of carbon, hydrogen, nitrogen, oxygen and sulfur are widespread in nature. Nevertheless, their relative abundance is not the same everywhere. This is due to kinetic isotope effects in enzymes and other physical principles such as equilibrium thermodynamics. Variations in isotope ratios offer unique insights into environmental pollution, trophic relationships in ecology, metabolic disorders and Earth history including climate history. Although classical isotope ratio mass spectrometry (IRMS) techniques still struggle to access intramolecular information like site-specific isotope abundance, electrospray ionization-Orbitrap mass spectrometry can be used to achieve precise and accurate intramolecular quantification of isotopically substituted molecules ('isotopocules'). This protocol describes two procedures. In the first one, we provide a step-by-step beginner's guide for performing multi-elemental, intramolecular and site-specific stable isotope analysis in unlabeled polar solutes by direct infusion. Using a widely available calibration solution, isotopocules of trifluoroacetic acid and immonium ions from the model peptide MRFA are quantified. In the second approach, nitrate is used as a simple model for a flow injection routine that enables access to a diverse range of naturally occurring isotopic signatures in inorganic oxyanions. Each procedure takes 2-3 h to complete and requires expertise only in general mass spectrometry. The workflows use optimized Orbitrap IRMS data-extraction and -processing software and are transferable to various analytes amenable to soft ionization, including metabolites, peptides, drugs and environmental pollutants. Optimized mass spectrometry systems will enable intramolecular isotope research in many areas of biology.

Oxygen Isotope Analysis of Nanomole Phosphate Using PO3- Fragment in ESI-Orbitrap-MS.

The oxygen isotope composition of phosphate is a useful tool for studying biogeochemical phosphorus cycling. However, the current Ag3PO4 method is not only tedious in PO43- extraction and purification but also requires a large-sized sample at the micromole level, thereby limiting its application. Here, we present an approach to measuring the oxygen isotope composition, δ18O, of dissolved phosphate at the nanomole level using electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap-MS). We compared the reproducibility of δ18O measurements using the H2PO4- ions (m/z = 97 and 99 for H2P16O4- and H2P18O16O3-, respectively) and using the PO3- fragment ions (m/z = 79 and 81 for P16O3- and P18O16O2-, respectively) generated by source fragmentation and by higher-energy collisional dissociation, respectively. The results demonstrate that phosphate δ18O can be more reliably measured by the PO3- ions than by the H2PO4- ions. PO3- generated by source fragmentation at 40 V achieved the highest reproducibility for δ18O based on precision tests. Furthermore, the mass spectrum for a 50:50 μM mixed solution of phosphate and sulfate revealed that PO3- ions resulting from source fragmentation at 40 V are the predominant species in the Orbitrap analyzer. Notably, P16O3- ions (m/z: 79) are not interfered with by 32S16O3- (m/z: 80) ions. This is in contrast to the case for 1H2P16O4- ions, which share the same m/z value with 1H32S16O4- ions and exhibit much lower signal intensity than HSO4- ions. Using the PO3- fragment method and six phosphate standards with a wide range of δ18O values, we obtained a calibration line with a slope of 0.94 (R2 = 0.98). The overall uncertainty for ESI-Orbitrap-MS phosphate δ18O measurement was 0.8‰ (n = 30; 1 SD). With much room for improvement, the PO3- fragment method presents a better approach to measuring the phosphate oxygen isotope composition, applicable to nanomole sample sizes in a liquid phase.

Molecular transformation of heavy oil during slurry phase hydrocracking process: A comparison between thermal cracking and hydrocracking

To systematically investigate the reaction mechanism of heavy oil in the slurry phase hydrocracking process, comparative experiments of thermal cracking and slurry phase hydrocracking of a residual oil were carried out. The molecular composition of sulfur and nitrogen compounds in the feedstock and their products was comprehensively characterized by gas chromatography and electrospray ionization Orbitrap mass spectrometry. The participation of hydrogen makes the apparent cracking rate in hydrocracking process significantly lower than that in the thermal cracking process, leading to a more controllable cracking degree and higher liquid yield. Nitrogen- and sulfur-containing aromatics with high molecular condensation degree are the key refractory heteroatoms because of large steric hindrance. Aromatics with ring number over 4 have high saturation reactivity, as well as the exposed five-membered heteroaromatic rings. The mutual influence of cracking, aromatic saturation, and hydrodeheteroatom during hydrocracking were also discussed according to bulk properties and molecular composition. The results deepen the understanding of the complex reaction network and mechanism of heavy oil hydrocracking process from both thermal reaction and hydrogenation perspectives, which will be instructive for the catalyst design and the process optimization.

Pattern Recognition Analysis of Metabolites in Escherichia coli Based on ESI-Orbitrap Mass Spectrometry.

To achieve rapid detection of carbapenem-resistant Escherichia coli strains, a pattern recognition method based on electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap MS) was used for the analysis of drug-resistant, and sensitive strains of metabolites were analyzed. Results of five clustering methods applied to analytical data of metabolites were evaluated using iso-phenotypic coefficients. The effectiveness of three methods, principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and orthogonal partial least squares discriminant analysis (OPLS-DA), was compared. Univariate statistics such as t-test and fold change (FC) were also used to examine the screened differential information. Both PLS-DA and OPLS-DA could achieve rapid identification of strain classes, and OPLS-DA was more powerful in screening 96 significantly different ions. This work is expected to be useful for rapid and accurate identification of strains.

Phytochemical analysis and in vitro and in vivo antioxidant properties of Plagiorhegma dubia Maxim as a medicinal crop for diabetes treatment

In traditional medicine, Plagiorhegma dubia Maxim (PD) is used to treat diabetes, irritability, insomnia, high fever, and coma. In this study, to identify the components in PD, we first performed three preliminary phytochemical tests, which were all positive for the presence of alkaloids. Next, we evaluated the total alkaloid content and performed 13 different in vitro antioxidant experiments for three solvent extracts of PD. According to the results, the methanol extract was selected for further research. Ultra-performance liquid chromatography with electrospray ionization Orbitrap mass spectrometry was used to identify 41 compounds in the methanol extract. Thirty-eight of these compounds were alkaloids, and the main components were magnoflorine, berberrubine, and betaine. Addition of the methanol extract to cooking oil increased the stability against oxidation and greatly reduced the peroxide value. Cell viability and oral acute toxicity studies in mice indicated that the methanol extract was relatively non-toxic. Histopathological examination and biochemical analysis showed that the methanol extract was protective against liver damage in rats induced by d-galactosamine. The methanol extract also showed a good antidiabetic effect for streptozotocin-induced diabetes in rats, where it lowered blood sugar levels and protected vital organs against damage. Lipid profile parameters and oxidative stress parameters also improved. The therapeutic effects towards diabetes and liver damage were attributed to the ability of the three main components in the methanol extract to resist oxidative stress. Our results show that the alkaloid-rich methanol extract of PD is potential candidate for treatment of diseases associated with oxidative imbalances. This understanding of the hepatoprotective effect and antidiabetic activity of PD provides new insight for its use as a substitute for Coptis chinensis and establishes a foundation for development of PD as an economic crop.

Study on molecular structure characteristics of natural dissolved organic nitrogen by use of negative and positive ion mode electrospray ionization Orbitrap mass spectrometry and collision-induced dissociation

Dissolved organic nitrogen (DON) in aquatic systems is an important component of the global nitrogen cycle. However, the molecular structural information of DON in natural water is still unknown. In this study, the molecular structural characteristics of DON molecules in three natural waters were studied by using negative and positive ion mode electrospray ionization (ESI) Orbitrap mass spectrometry and collision-induced dissociation (CID). The DON compounds in these natural water samples could be selectively ionized by a positive ESI source with formic acid as the ionization promoter. A fraction of DON may exist as amphoteric substance. Then, possible chemical structures were assigned for some of these DON molecules by CID. Possible O-containing functional groups could be assigned as carboxyl, hydroxyl, carbonyl and methoxyl in negative/positive ESI tandem mass spectra, and neutral loss of NH3 corresponding to amino groups was observed for the first time in a positive ESI CID MSMS analysis, which demonstrated that a fraction of DON in natural water may exist as amino acid-like compounds. The results demonstrate that the positive/negative ESI CID Orbitrap MSMS method could provide valuable molecular structure information on DON in natural water.

Differential Accumulation of Short-, Medium-, and Long-Chain Chlorinated Paraffin in Free-Range Laying Hens from an E-Waste Recycling Area.

Chlorinated paraffins (CPs) are environmental pollutants of emerging concern. Long-chain CPs (LCCPs) are considered of lesser concern than other CPs in food due to their lower accumulation in most organisms. However, LCCPs have been shown to accumulate preferentially in birds. We used ultrahigh-performance liquid chromatography combined with electrospray ionization Orbitrap mass spectrometry (UPLC-ESI-Orbitrap MS) to analyze CPs (C10-26Cl4-12) in tissues of free-range hens, their feed, and local soils. Feed was found to be the main source of CP intake. The CP carbon chain length had little impact on their absorption. C18-CPs were excreted in preference to C13-CPs by laying. The metabolic elimination rates of CPs (0.2 μg/mL) estimated using chicken liver microsomes were in the order C12Cl6 (91%) > C12Cl8 (57%) > C18Cl6 (12%) > C18Cl8 (6%). CPs with longer carbon chains accumulated preferentially in muscle and adipose tissues, and the accumulation of specific carbon chain lengths was related to the content and composition of different CPs in the intake source.

Minimizing ion competition boosts volatile metabolome coverage by secondary electrospray ionization orbitrap mass spectrometry

Secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS) is an emerging technique for the detection of volatile metabolites. However, sensitivity and reproducibility of SESI-HRMS have limited its applications in untargeted metabolomics profiling. Ion suppression in the SESI source has been considered to be the main cause. Here, we show that besides ion suppression, ion competition in the C-trap of Orbitrap instruments is another important factor that influences sensitivity and reproducibility of SESI-MS. Instead of acquiring the full mass-to-charge ratio (m/z) range, acquisition of consecutive m/z windows to minimize the ion competition effect allows the detection of more features. m/z window ranges are optimized to fill the C-trap either with an equal number of features or an equal cumulative intensity per window. Considering a balance between maximizing scanning speed and minimizing ion competition, splitting the m/z = 50–500 range into 4 windows is selected for measuring human breath and bacterial culture samples on SESI-Orbitrap MS, corresponding to a duty cycle of 2.3 s at a resolution of 140′000. In a small cohort of human subjects, the proposed splitting into 4 windows allows three times more features to be detected compared to the classical full m/z range method.

Characterization of Severely Biodegraded Crude Oils Using Negative-Ion ESI Orbitrap MS, GC-NCD and GC-SCD: Insights into Heteroatomic Compounds Biodegradation

A slightly and two severely biodegraded crude oils with the same origin were analysed using negative-ion electrospray ionization Orbitrap mass spectrometry (ESI Orbitrap MS), gas chromatography-nitrogen chemiluminescence detector (GC-NCD), and GC-sulfur chemiluminescence detector (GC-SCD) to investigate the composition of heteroatomic compounds and their fate during severe biodegradation and to provide insights into biodegradation pathway of hopanes, nitrogen- and sulfur-containing compounds. Twelve heteroatomic compound classes, including O1–O5, N1, N2, N1O1–N1O3, N1S1 and O3S1, were detected and assigned unambiguous molecular formulae. The O1 species are likely phenols with additional naphthenic and/or aromatic rings. Carboxylic acids (O2 species) are originated from oxidation of hydrocarbons, and the tricyclic naphthenic acids are the most resistant, followed by bicyclics. Hopanes could be biodegraded by demethylation or by unstable hopanoic acids as intermediates to yield 25-norhopanes. The N1 species are pyrrolic compounds with naphthenic and/or aromatic rings and are dominated by carbazole analogues. Carbazoles with more aromatic rings are more resistant to biodegradation. The N1 species could be converted to N1O1 and N1O2 compounds via ring-opening and hydroxylation pathways. The N1S1 species contain a pyrrolic and cyclic sulfide structure, which are highly recalcitrant to biodegradation. Benzothiophenes and dibenzothiophenes might be biodegraded via the complete pathway or the sulfur-specific pathway rather than by other pathways to yield acidic oxygenated sulfur compounds.

The acid and neutral nitrogen compounds characterized by negative ESI Orbitrap MS in a heavy oil before and after oxidation

One heavy crude oil from Liaohe Basin, NE China and its oxidized counterparts at 200 and 400 °C have been characterized geochemically by negative-ion electrospray ionization Orbitrap mass spectrometry to investigate the variation of acid and neutral nitrogen compounds during in-situ combustion. The heteroatom compounds of acid and neutral nitrogen detected in the samples are mainly N1, N1O1, N1O2, O1, O2, O3 and O4 classes, dominated by N1, O1 and O2. The N1 class predominated by carbazole and benzocarbazole with double bond equivalents (DBE) 9 and 12, is relatively stable and resistant to oxidation, while the N1O1 and N1O2 classes vary without a clear trend during oxidation. The O1 class is generally low in raw sample and the 200 °C oxidized oil but increases sharply in the 400 °C oxidized oil. The O2 class is peaked in the 200 °C oxidized oil but its relative concentration declines drastically in the 400 °C oxidized oil. The O1 and O2 class compounds show a similar DBE and carbon number (CN) distribution trend with increasing temperatures. Lower DBE and CN compounds are enriched in the 400 °C oxidized oil after alkyl side chain cleavage, where small proportion of high DBE compounds derived from aromatization and condensation has also been observed. The relative abundance of O1 and O2 species with specific DBE values and carbon number ranges are sensitive to in-situ thermal upgrading and ratios of DBE1/DBE4-O1 and DBE1/DBE3-O2 endure the potential as geochemical proxies to monitor the degree of oil upgrading.

Pesticide residues quantification in frozen fruit and vegetables in Chilean domestic market using QuEChERS extraction with ultra-high-performance liquid chromatography electrospray ionization Orbitrap mass spectrometry

Pesticide residues on foods are a global concern due to the impact on human health. Many countries have adopted regulations to establish Maximum Residue Levels (MRLs) to control use of pesticides. This study aimed to determine pesticide residues in frozen fruit and vegetables from Chilean retail stores using UHPLC-Orbitrap MS and QuEChERS™ multiresidue-extraction kit. 237 samples of frozen produce were sampled from different supermarkets and times during the year. Abamectin, Chlorpyrifos, Imidacloprid, Iprodione, λ-cyhalothrin, Spinosad A, and Spinosad D were quantified. Results showed that Iprodione, Spinosad A, and D were the most detected molecules. Pesticides were detected in 96.6% of samples and 21 samples exceeded MRL. Corn and faba beans showed the highest concentration of Iprodione with an average of 6.7 and 5.4 mg/Kg, respectively. Existence of nonconformity in samples highlights the importance to control pesticide residues of Chilean frozen produce, since it represents a latent health threat on consumers.

Characterization of Athabasca lean oil sands and mixed surficial materials: Comparison of capillary electrophoresis/low-resolution mass spectrometry and high-resolution mass spectrometry.

Oil sands mining in Alberta, Canada, requires removal and stockpiling of considerable volumes of near-surface overburden material. This overburden includes lean oil sands (LOS) which cannot be processed economically but contain sparingly soluble petroleum hydrocarbons and naphthenic acids, which can leach into environmental waters. In order to measure and track the leaching of dissolved constituents and distinguish industrially derived organics from naturally occurring organics in local waters, practical methods were developed for characterizing multiple sources of contaminated water leakage. Capillary electrophoresis/positive-ion electrospray ionization low-resolution time-of-flight mass spectrometry (CE/LRMS), high-resolution negative-ion electrospray ionization Orbitrap mass spectrometry (HRMS) and conventional gas chromatography/flame ionization detection (GC/FID) were used to characterize porewater samples collected from within Athabasca LOS and mixed surficial materials. GC/FID was used to measure total petroleum hydrocarbon and HRMS was used to measure total naphthenic acid fraction components (NAFCs). HRMS and CE/LRMS were used to characterize samples according to source. The amounts of total petroleum hydrocarbon in each sample as measured by GC/FID ranged from 0.1 to 15.1mg/L while the amounts of NAFCs as measured by HRMS ranged from 5.3 to 82.3mg/L. Factors analysis (FA) on HRMS data visually demonstrated clustering according to sample source and was correlated to molecular formula. LRMS coupled to capillary electrophoresis separation (CE/LRMS) provides important information on NAFC isomers by adding analyte migration time data to m/z and peak intensity. Differences in measured amounts of total petroleum hydrocarbons by GC/FID and NAFCs by HRMS indicate that the two methods provide complementary information about the nature of dissolved organic species in a soil or water leachate samples. NAFC molecule class Ox Sy is a possible tracer for LOS seepage. CE/LRMS provides complementary information and is a feasible and practical option for source evaluation of NAFCs in water.

Fate and behavior of oil sands naphthenic acids in a pilot-scale treatment wetland as characterized by negative-ion electrospray ionization Orbitrap mass spectrometry

Large volumes of oil sands process-affected water (OSPW) are generated during the extraction of bitumen from oil sands in the Athabasca region of northeastern Alberta, Canada. As part of the development of treatment technologies, molecular characterization of naphthenic acids (NAs) and naphthenic acid fraction compounds (NAFC) in wetlands is a topic of research to better understand their fate and behavior in aquatic environments. Reported here is the application of high-resolution negative-ion electrospray Orbitrap-mass spectrometry for molecular characterization of NAs and NAFCs in a non-aerated constructed treatment wetland. The effectiveness of the wetlands to remove OSPW-NAs and NAFCs was evaluated by monitoring the changes in distributions of NAFC compounds in the untreated sample and non-aerated treatment system. After correction for measured evapotranspiration, the removal rate of the classical NAs followed approximately first-order kinetics, with higher rates observed for structures with relatively higher number of carbon atoms. These findings indicate that constructed wetland treatment is a viable method for removal of classical NAs in OSPW. Work is underway to evaluate the effects of wetland design on water quality improvement, preferential removal of different NAFC species, and reduction in toxicity.

Chemical Analysis of Astragali Complanati Semen and Its Hypocholesterolemic Effect Using Serum Metabolomics Based on Gas Chromatography-Mass Spectrometry.

The hypocholesterolemic protective effect of the dried seed of Astragalus complanatus (ACS) was investigated in rats fed with normal diet, high cholesterol diet (HCD), and HCD plus 70% ethanol extract of ACS (600 mg/kg/day) by oral gavage for four weeks. ACS extract was tested to be rich in antioxidants, which may be contributed to its high content of phenolic compounds. Consumption of ACS remarkably suppressed the elevated total cholesterol (p < 0.01) and LDL-C (p < 0.001) induced by HCD. Chemical constituents of ACS extract were analyzed by ultra-performance liquid chromatography coupled with electrospray ionization orbitrap mass spectrometry and the results showed that the ACS extract mainly consisted of phenolic compounds including flavonoids and flavonoid glycosides. In addition, based on the serum fatty acid profiles, elucidated using gas chromatography-mass spectrometry, free and esterified fatty acids including docosapentaenoic acid, adrenic acid, dihomo-γ-linolenic acid and arachidonic acid were regulated in ACS treatment group. Western blot results further indicated the protein expression of peroxisome proliferator-activated receptor alpha (PPARα) (p < 0.05) in liver was upregulated in ACS treatment group. To conclude, our results clearly demonstrated that ACS provides beneficial effect on lowering HCD associated detrimental change.

Nitrogen-Containing Low Volatile Compounds from Pinonaldehyde-Dimethylamine Reaction in the Atmosphere: A Laboratory and Field Study.

Pinonaldehyde, which is among the most abundant oxidation products of α-pinene, and dimethylamine were selected to study the formation of N-containing low volatile compounds from aldehyde-amine reactions in the atmosphere. Gas phase reactions took place in a Tedlar bag, which was connected to a mass spectrometer ionization source via a short deactivated fused silica column. In addition to on-line analysis, abundance of gaseous precursors and reaction products were monitored off-line. Condensable products were extracted from the bag's walls with a suitable solvent and analyzed by gas chromatography coupled to chemical ionization high-resolution quadrupole time-of-flight mass spectrometry and by ultra-high-performance liquid chromatography coupled to electrospray ionization Orbitrap mass spectrometry. The reactions carried out resulted in several mid-low vapor pressure nitrogen-containing compounds that are potentially important for the formation of secondary organic aerosols in the atmosphere. Further, the presence of brown carbon, confirmed by liquid chromatography-UV-vis-mass spectrometry, was observed. Some of the compounds identified in the laboratory study were also observed in aerosol samples collected at SMEAR II station (Hyytiälä, Finland) in August 2015 suggesting the importance of aldehyde-amine reactions for the aerosol formation and growth.

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry

In this study we evaluated a method for the characterization of complexes, formed in different relative ratios of mercury(II) to dicysteinyl tetrapeptide, by electrospray ionization orbitrap mass spectrometry. This strategy is based on previous successful characterization of mercury-dicysteinyl complexes involving tripeptides by utilizing mass spectrometry among other techniques. Mercury(II) chloride and a dicysteinyl tetrapeptide were incubated in a degassed buffered medium at varying stoichiometric ratios. The complexes formed were subsequently analyzed on an electrospray mass spectrometer consisting of a hybrid linear ion- and orbi- trap mass analyzer. The electrospray ionization mass spectrometry (ESI-MS) spectra were acquired in the positive mode and the observed peaks were then analyzed for distinct mercury isotopic distribution patterns and associated monoisotopic peak. This work demonstrates that an accurate stoichiometry of mercury and peptide in the complexes formed under specified electrospray ionization conditions can be determined by using high resolution ESI MS based on distinct mercury isotopic distribution patterns.

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry.

In this study we evaluated a method for the characterization of complexes, formed in different relative ratios of mercury(II) to dicysteinyl tetrapeptide, by electrospray ionization orbitrap mass spectrometry. This strategy is based on previous successful characterization of mercury-dicysteinyl complexes involving tripeptides by utilizing mass spectrometry among other techniques. Mercury(II) chloride and a dicysteinyl tetrapeptide were incubated in a degassed buffered medium at varying stoichiometric ratios. The complexes formed were subsequently analyzed on an electrospray mass spectrometer consisting of a hybrid linear ion- and orbi- trap mass analyzer. The electrospray ionization mass spectrometry (ESI-MS) spectra were acquired in the positive mode and the observed peaks were then analyzed for distinct mercury isotopic distribution patterns and associated monoisotopic peak. This work demonstrates that an accurate stoichiometry of mercury and peptide in the complexes formed under specified electrospray ionization conditions can be determined by using high resolution ESI MS based on distinct mercury isotopic distribution patterns.