Pressure Chemical Ionization Mass Research Articles

Extending the known range of glycerol ether lipids in the environment: structural assignments based on tandem mass spectral fragmentation patterns

Glycerol-based alkyl ether lipids are ubiquitous components in marine sediments. In order to explore their structural diversity and biological sources, marine sediment samples from diverse environments were analyzed and the mass spectra of widely distributed, novel glycerol di- and tetraethers were examined systematically. Lipid extracts of twelve globally distributed marine subsurface sediments were analyzed by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Tandem mass (MS/MS) spectra of compounds were obtained with a quadrupole time-of-flight (qTOF) mass spectrometer. In addition to the well-established isoprenoidal glycerol dialkyl glycerol tetraether (isoprenoidal GDGT) and branched GDGT, suites of novel lipids were detected in all studied samples. These lipids include the following classes of tentatively identified compounds: isoprenoidal glycerol dialkanol diether (isoprenoidal GDD), hydroxylated isoprenoidal GDGT (OH-GDGT), hybrid isoprenoidal/branched GDGT (IB-GDGT), hydroxylated isoprenoidal GDD (OH-GDD), overly branched GDGT (OB-GDGT), sparsely branched GDGT (SB-GDGT) and an abundant H-shaped GDGT with the [M+H](+) ion of m/z 1020 (H-1020). Characteristic MS/MS fragmentation patterns provided mass spectral 'fingerprints' for the recognition of diverse and prominent glycerol ether lipids. The ubiquitous distribution and substantial abundance of these glycerol ethers, as well as their structural variability, suggest a significant ecological role of their source organisms in various marine environments.

Analysis of carbohydrates by atmospheric pressure chloride anion attachment tandem mass spectrometry

The ability to characterize oligosaccharides directly in complex mixtures would greatly benefit many research efforts focused on the development of biofuels from lignocellulosic biomass. We report here on the utility of chloride anion attachment in atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) tandem mass spectrometry for MW determination and structural elucidation of several mono-, di- and oligosaccharides directly without sample pretreatment or derivatization. Chloride anion forms stable adducts with these sugars upon ESI or APCI, which can be readily identified due to the chlorine isotope pattern. Fragment anions or other product anions are usually not observed, which is beneficial for mixture analysis. Upon collisional activation in MS2 experiments, these adducts readily lose HCl, which helps verify the molecular weight of each analyte. Isolating the resulting anion and subjecting it to further collision-activated dissociation experiments (MSn; n=3–4) until no ion signal remains yields useful structural information. Examination of equimolar mixtures of mono-, di- and oligosaccharides and mixtures of enzymatically digested biomass demonstrates the ability of this methodology to ionize all the components of the mixtures without bias and with nearly equal efficiency.

High molecular weight non‐polar hydrocarbons as pure model substances and in motor oil samples can be ionized without fragmentation by atmospheric pressure chemical ionization mass spectrometry

High molecular weight non-polar hydrocarbons are still difficult to detect by mass spectrometry. Although several studies have targeted this problem, lack of good self-ionization has limited the ability of mass spectrometry to examine these hydrocarbons. Failure to control ion generation in the atmospheric pressure chemical ionization (APCI) source hampers the detection of intact stable gas-phase ions of non-polar hydrocarbon in mass spectrometry. Seventeen non-volatile non-polar hydrocarbons, reported to be difficult to ionize, were examined by an optimized APCI methodology using nitrogen as the reagent gas. All these analytes were successfully ionized as abundant and intact stable [M-H](+) ions without the use of any derivatization or adduct chemistry and without significant fragmentation. Application of the method to real-life hydrocarbon mixtures like light shredder waste and car motor oil was demonstrated. Despite numerous reports to the contrary, it is possible to ionize high molecular weight non-polar hydrocarbons by APCI, omitting the use of additives. This finding represents a significant step towards extending the applicability of mass spectrometry to non-polar hydrocarbon analyses in crude oil, petrochemical products, waste or food.

Quantitative Real-Time Monitoring of Chemical Reactions by Autosampling Flow Injection Analysis Coupled with Atmospheric Pressure Chemical Ionization Mass Spectrometry

Although qualitative and/or semiquantitative real-time monitoring of chemical reactions have been reported with a few mass spectrometric approaches, to our knowledge, no quantitative mass spectrometric approach has been reported so far to have a calibration valid up to molar concentrations as required by process control. This is mostly due to the absence of a practical solution that could well address the sample overloading issue. In this study, a novel autosampling flow injection analysis coupled with an atmospheric pressure chemical ionization mass spectrometry (FIA/APCI-MS) system, consisting of a 1 μL automatic internal sample injector, a postinjection splitter with 1:10 splitting ratio, and a detached APCI source connected to the mass spectrometer using a 4.5 in. long, 0.042 in. inner diameter (ID) stainless-steel capillary, was thus introduced. Using this system together with an optional FIA solvent modifier, e.g., 0.05% (v/v) isopropylamine, a linear quantitative calibration up to molar concentration has been achieved with 3.4-7.2% relative standard deviations (RSDs) for 4 replicates. As a result, quantitative real-time monitoring of a model reaction was successfully performed at the 1.63 M level. It is expected that this novel autosampling FIA/APCI-MS system can be used in quantitative real-time monitoring of a wide range of reactions under diverse reaction conditions.

Identification of Geometrical Isomers and Comparison of Different Isomeric Samples of Astaxanthin

A high-performance liquid chromatographic (HPLC) analysis system for isomeric astaxanthin was developed. The separation system consisted of a C(30) column and an elution system of methanol/MTBE/water/dichloromethane (77:13:8:2, v/v/v/v). Using the combination of HPLC diode array detector and HPLC atmospheric pressure chemical ionization mass spectrometry, 11 geometrical isomers and 4 epoxides of astaxanthin were successfully identified. Referred to crystal, only isomerization with different degrees was found for solvent dissolving and iodine catalysis, while melting of astaxanthin caused isomerization, slight oxidation, and more noticeable polymerization confirmed by gel permeation chromatography. Chemical changes in isomeric samples all caused a decrease in UV content. The vibrational spectra (infrared and Raman) showed that epoxide was the only new functional group generated for melting. Changes of several key bands and formations of new bands were found in iodine catalysis and melting samples because of isomerization. Practical Application: Eleven geometrical isomers and 4 epoxides, which were normally generated for solvent dissolving, iodine catalysis, and melting of astaxanthin, have been identified by C(30) -HPLC-MS technology. Furthermore, different samples were measured by gel permeation chromatography, UV, infrared, and Raman, based on the analysis of messages, the effect of each processing was well understood.

DETERMINATION AND IDENTIFICATION OF FATTY ACIDS IN MICROULA SIKKIMENSIS SEED OIL USING 1,2-BENZOCARBAZOLE-9-ETHYL-P-TOLUENESULFONATE AS A NOVEL LABELING REAGENT BY HPLC WITH FLUORESCENCE DETECTION AND APCI-MS

Using 1,2-benzocarbazole-9-ethyl-p-toluenesulfonate (BCETS) as the labeling reagent, a sensitive method for the determination of fatty acids by high performance liquid chromatography (HPLC) with fluorescence detection has been developed. The BCETS could easily and quickly label fatty acids in the presence of the K2CO3 catalyst at 90°C for 30 min in N,N-dimethylformamide solvent. All the tested fatty acid derivatives were separated on a reversed-phase Eclipse XDB-C8 column by HPLC in conjunction with gradient elution. The identification was carried out by post-column atmospheric pressure chemical ionization mass spectrometry (APCI/MS) in positive ion detection mode. The fluorescence excitation and emission wavelengths of the derivatives were at λex 279 nm and λem 380 nm, respectively. Linear correlation coefficients for all fatty acid derivatives are more than 0.9994. Detection limits, at a signal-to-noise ratio of 3:1, were 0.21–0.99 µg/L for the labeled fatty acids. In this study, fatty acids from the extracted Microula sikkimensis Hemsl (M. sikkimensis H.) seed were sensitively determined. It was found that the seed oil mainly contained Oleic acid, Linoleic acid, α-Linolenic acid, Hexadecanoic acid, Stearidonic acid, γ-Linolenic acid, and Eicosenoic acid. M. sikkimensis H. seed oil was rich in unsaturated fatty acids and may be used as high-quality edible oil for its health benefits.

A study of the thermodynamics of retention of block (co)oligomers using high-performance liquid chromatography/mass spectrometry

Chromatographic behavior of block (co)oligomers of oxyethylene (EO) and oxypropylene (PO) surfactants in reversed-phase HPLC (RP-HPLC) was investigated. The retention of EO/PO block (co)oligomers depends on the distribution of the individual monomer repeat units, but the sequence of the individual blocks also plays a (less significant) role. The enthalpic and entropic contributions of the EO and PO repeat units to the retention were determined from the data measured at changing temperature. In RP-HPLC, the effect of the repeat PO units on separation is higher than the influence of the repeat EO units. In addition to the enthalpic contributions, the retention is significantly influenced by the entropy (possibly by the change of conformation and solvation of adsorbed molecules); dual molar mass distribution according to the number of EO and PO units complicates correct assignment of the chromatographic peaks to the individual (co)oligomers in complex samples based only on the chromatographic retention data. In spite of imperfect chromatographic separation, HPLC coupled with positive ion mode atmospheric pressure chemical ionization mass spectrometry allow identifying unambiguously the dual monomer distribution in the samples of EO–PO block (co)oligomers.

Isolation and identification of lutein esters, including their regioisomers, in tritordeum (×Tritordeum Ascherson et Graebner) grains: Evidence for a preferential xanthophyll acyltransferase activity

Liquid chromatography in conjunction with UV–visible spectroscopy and atmospheric pressure chemical ionisation (APCI) mass spectrometry has been used for the structural assignment of the lutein esters, including the regioisomeric forms, naturally occurring in the endosperm of tritordeum (×Tritordeum Ascherson et Graebner), a novel cereal. The distinctive mass spectrometry fragmentation pattern of lutein, characterized by a favored loss of the moieties at the position 3′ of the ε-end ring, allowed an unambiguous structural identification of four monoesters (lutein 3′-O-linoleate, lutein 3-O-linoleate, lutein 3′-O-palmitate, lutein 3-O-palmitate) and four diesters (lutein dilinoleate, lutein 3′-O-linoleate-3-O-palmitate, lutein 3′-O-palmitate-3-O-linoleate, lutein dipalmitate). This is the first time that the regioisomers of carotenoid esters have been identified in a cereal. Evidences for a preferential xanthophyll acyltransferase activity regarding the position (3 or 3′) and the acyl moiety are discussed. Further studies should be carried out in order to identify the acyltransferase enzymes and the acyl donor molecules involved in the xanthophyll esterification process.

Separation of Asphaltenes by Reversed-Phase Liquid Chromatography with Fraction Characterization

The use of a 4.6 × 250 mm, 5 μm cyanopropyl column is effective for the liquid chromatography (LC) separation of asphaltenes with sequential ultraviolet (UV) and florescence detection. The mobile-phase composition is an optimized gradient from acetonitrile (MeCN) and water to N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF). A low flow rate of 0.5 mL min–1 is used to maintain lower operating pressure to minimize aggregate formation. Using a 0.02 g L–1 asphaltene sample for preliminary optimization, three peaks, with two partially resolved, are evident in the fluorescence chromatogram. The UV chromatogram revealed an extra weakly retained peak, suggesting aggregates that quench fluorescence. Aggregation of asphaltenes increases with time up to about 10 h and is dependent upon the choice of sample solvent. On the basis of the reversed-phase mobile-phase gradient, the relative polarity of the peaks from least to most retained can be estimated over the polarity index (P′) range from about 6.3–4.3 on a scale of 0.1 for hexane (least polar) to 10.6 for water (most polar). The sample concentration is increased to 1 g L–1 for separation and collection of 12 fractions. Selected fractions are subjected to characterization using atmospheric pressure chemical ionization mass spectrometry (APCI–MS) using a linear quadrupole ion trap (LQIT). The variation of the molecular-weight distribution of the asphaltenes for the 12 fractions is fairly constant, indicating that the retention mechanism is not controlled by size exclusion but likely a partitioning/adsorption mechanism.

Determination of Carotenoids, Total Phenolic Content, and Antioxidant Activity of Arazá (Eugenia stipitata McVaugh), an Amazonian Fruit

The fruit of Arazá (Eugenia stipitata McVaugh) native to the Colombian Amazon is considered a potentially economically valuable fruit for the Andean economy due to its novel and unique taste. The fruit has an intense yellow color, but its chemical composition and properties have not been well studied. Here we report the identification and quantitation of carotenoids in the ripe fruit using high performance liquid chromatography (HPLC) with photodiode array detector (PDA) and atmospheric pressure chemical ionization (APcI) mass spectrometry (MS/MS). The qualitative carotenoid profile of the fruit according to maturity stage was also observed. Furthermore, antioxidant activity of the peel and pulp were assessed using the ferric reducing ability of plasma (FRAP), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods, in addition to chemical indexes and total phenolic content. Multiple carotenoids were identified in the peel and pulp including four xanthophylls (free and esterified as their mono and diesters) and two carotenes. One of the xanthophylls was tentatively identified as zeinoxanthin, while the others were identified as lutein, zeaxanthin, and β-cryptoxanthin. Carotenes included α-carotene and β-carotene. The total carotenoid content was significantly higher in the peel (2484 ± 421 μg/100 g FW) than in the pulp (806 ± 348 μg/100 g FW) with lutein, β-cryptoxanthin, and zeinoxanthin as the major carotenoid components. The unique carotenoid composition of this fruit can differentiate it from other carotenoid-rich fruits and perhaps be useful in authentication procedures. Overall, results from this study suggest that Colombian Arazá may be a good edible source of carotenoids important in retinal health as well as carotenoids with provitamin A activity. Therefore, Arazá fruit can be used as a nutraceutical ingredient and in production of functional foods in the Colombian diet.

Identification of the double-bond position in fatty acid methyl esters by liquid chromatography/atmospheric pressure chemical ionisation mass spectrometry

Fatty acid methyl esters (FAMEs) were analysed by reversed-phase HPLC coupled with atmospheric pressure chemical ionisation (APCI) mass spectrometry. The chromatographic separations of the FAMEs were optimised using acetonitrile or binary acetonitrile gradients and C18 or C30 columns. The gas-phase reactions of acetonitrile and unsaturated FAMEs in the APCI source provided [M+C3H5N]+ adducts. When fragmented, these adducts yielded diagnostic ions, allowing the unambiguous localisation of double bonds. The formation and fragmentation of the acetonitrile-related adduct was utilised for the structural characterisation of the FAMEs separated by HPLC. The APCI-MS detection of FAMEs encompassed a full-spectrum scan (providing information on the number of carbons and double bonds) and a data-dependent MS/MS scan of the [M+C3H5N]+ ions (the position of the double bonds). The utility of this approach was demonstrated using a mixture of FAMEs from blackcurrant-seed oil. All the unsaturated fatty acids known to exist in the sample were correctly identified and several others were newly discovered. In terms of sensitivity, HPLC/APCI-MS appeared to be comparable to GC/EI-MS.

Differentiation of underivatized monosaccharides by atmospheric pressure chemical ionization quadrupole time‐of‐flight mass spectrometry

Differentiation of underivatized monosaccharides is essential in the structural elucidation of oligosaccharides which are closely involved in many life processes. So far, such differentiation has been usually achieved by electrospray ionization mass spectrometry (ESI-MS). As an alternative to ESI-MS, atmospheric pressure chemical ionization mass spectrometry (APCI-MS) should provide complementary results. A quadrupole time-of-flight (QTOF) mass spectrometer with accurate mass measurement ability was used with an APCI heated nebulizer ion source because we believe that a recently published article using a single quadrupole mass spectrometer assigned incorrect identities for APCI ions from hexoses. Using APCI-QTOF, the MS(2) and pseudo-MS(3) mass spectra of 11 underivatized monosaccharides were obtained under various collision voltages. The mass spectra were carefully interpreted after accurate mass measurement. Differentiation of three hexoses was achieved by different MS(2) spectra of their [M + NH(4)](+) and [M - H](-) ions. The MS(2) spectra of the [M + NH(4)](+) ions were also used to distinguish methyl α-D-glucose and methyl β-D-glucose, while the pseudo-MS(3) spectra of the [M + H](+) ions were utilized to differentiate the three hexosamine and N-acetylhexosamine stereoisomers. Unique [M + O(2)](-) ions were observed and their distinctive fragmentation patterns were utilized to differentiate the three hexosamine stereoisomers. Although ESI coupled with single or triple quadrupole and ion trap mass spectrometers has been widely utilized in the differentiation of monosaccharides, this report demonstrated that APCI-QTOF-MS had its own advantages in achieving the same goal.

Abstract LB-10: Distribution and potency of anti-proliferative arachidonic acid metabolites

Abstract Eicosanoids participate in the dysregulation of cell proliferation during tumorigenesis. The up-regulation of cyclooxygenase-2 (COX-2) and down-regulation of 15-prostaglandin dehydrogenase (15-PGDH) have been linked to the switch for a pro-proliferative and pro-angiogenic tumor microenvironment. Previous studies have characterized the effects of increased prostaglandin E2 in tumor progression but the role of many other endogenous lipid mediators has yet to be determined. COX-2 can metabolize arachidonic acid (AA) to hydroxyeicosatetraenoic acids (HETEs), which in turn can be further oxidized by dehydrogenases into oxo-eicosatetraenoic acids (oxo-ETEs). We have previously reported that 11-oxo-ETE and 15-oxo-ETE are major COX-2/15-PGDH derived metabolites formed from human cells expressing COX-2 treated with AA. Although no known G-protein coupled receptor has been reported for either of these metabolites, both 11-oxo- and 15-oxo-ETE have been described from human clinical samples. This study provides a description of the uptake and distribution of 11-oxo-ETE and 15-oxo-ETE as well as their anti-proliferative activity in both human umbilical vein endothelial cells (HUVECs) and LoVo human colon adenocarcinoma cells. Quantification of the intracellular and extracellular levels of 11-oxo- and 15-oxo-ETE was conducted using liquid chromatography electron capture atmospheric pressure chemical ionization mass spectrometry with [13C]-labeled 15-oxo-ETE as an internal standard. The intracellular concentrations of 11-oxo- and 15-oxo-ETE reached peak amounts within 1h followed by a rapid decline. Earlier studies have indicated that glutathione (GSH)-S-transferase further metabolized 11-oxo-ETE to form the 11-oxo-ETE-GSH (OEG)-adduct. In additional experiments, pretreatment with ethacrynic acid (EA), a known inhibitor of GSTs, increased recovery from the cellular extract. In addition, the methyl-ester of both 11-oxo- and 15-oxo-ETE was used for the targeted intracellular delivery of these COX-2/15-PGDH derived eicosanoids. Finally, we have shown that both 11-oxo- and 15-oxo-ETE as well as their methyl ester derivatives significantly inhibit cell proliferation as determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell proliferation assay and Bromodeoxyuridine (BrdU) incorporation in multiple human cell lines. The present study has established the cellular uptake of the short-lived COX-2/15-PGDH derived eicosanoids 11-oxo- and 15-oxo-ETE and potent inhibition of new DNA synthesis and proliferation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-10. doi:1538-7445.AM2012-LB-10

Development and comparison of three liquid chromatography–atmospheric pressure chemical ionization/mass spectrometry methods for determining vitamin D metabolites in human serum

Liquid chromatographic methods with atmospheric pressure chemical ionization mass spectrometry were developed for the determination of the vitamin D metabolites 25-hydroxyvitamin D2 (25(OH)D2), 25-hydroxyvitamin D3 (25(OH)D3), and 3-epi-25-hydroxyvitamin-D3 (3-epi-25(OH)D3) in the four Levels of SRM 972, Vitamin D in Human Serum. One method utilized a C18 column, which separates 25(OH)D2 and 25(OH)D3, and one method utilized a CN column that also resolves the diastereomers 25(OH)D3 and 3-epi-25(OH)D3. Both methods utilized stable isotope labeled internal standards for quantitation of 25(OH)D2 and 25(OH)D3. These methods were subsequently used to evaluate SRM 909c Human Serum, and 25(OH)D3 was the only vitamin D metabolite detected in this material. However, SRM 909c samples contained matrix peaks that interfered with the determination of the [2H6]-25(OH)D3 peak area. The chromatographic conditions for the C18 column were modified to remove this interference, but conditions that separated the matrix peaks from [2H6]-25(OH)D3 on the CN column could not be identified. The alternate internal standard [2H3]-25(OH)D3 did not suffer from matrix interferences and was used for quantitation of 25(OH)D3 in SRM 909c. During the evaluation of SRM 909c samples, a third method was developed using a pentafluorophenylpropyl column that also separates the diastereomers 25(OH)D3 and 3-epi-25(OH)D3. The 25(OH)D3 was measured in SRM 909c using all three methods, and the results were compared.

Efficient liquid chromatographic analysis of mono-, di-, and triglycerols using silver thiolate stationary phase

We show that the characterization of mono-, di- and triglycerols can be readily accomplished by high performance liquid chromatography (HPLC) with silver(I)-mercaptopropyl modified silica gel, or silver thiolate chromatographic material (AgTCM), which can be used with evaporative light scattering detection (ELSD) or atmospheric pressure chemical ionization mass spectroscopy (APCI-MS). Separation of triglycerols varying by degrees of unsaturation and cis/trans configuration in common oil samples can be achieved using a simple linear gradient of hexane and acetone. In addition to double bonds, AgTCM also displays major selectivity for compounds with different levels of polarity, allowing for efficient separation between mono-, di- and triglycerols. In comparison to conventional reversed phase columns, AgTCM produces simple chromatograms for rapid assessment of degrees of unsaturation and the amount of trans fats in triglycerides, which are central issues to food quality determination. In comparison to previous silver-ion based HPLC separations, AgTCM–HPLC based column offers greatly enhanced stability, inertness, durability, and reproducibility allowing routine coupling of the HPLC with a mass spectrometer for detection.

Mass spectrometric elucidation of triacylglycerol content of Brevoortia tyrannus (menhaden) oil using non-aqueous reversed-phase liquid chromatography under ultra high pressure conditions

A non-aqueous reversed phase high performance liquid chromatography method was developed, and optimized for triacylglycerol analysis in a Brevoortia tyrannus (menhaden) oil sample. Four columns were serially coupled to tackle such a task, for a total length of 60cm of shell-packed stationary phase, and operated under ultra high pressure conditions. As detection, positive-ion atmospheric pressure chemical ionization mass spectrometry was used to attain identification of the analyzed sample components. A number of 137 triacylglycerols containing up to 19 fatty acids, with 14–22 carbon atom alkyl chain length and 0–6 double bonds, were positively identified in the complex lipidic sample. This is the first work that reports an extensive characterization of the triacylglycerol fraction of menhaden oil.

Regioisomer separation and identification of triacylglycerols containing vaccenic and oleic acids, and α- and γ-linolenic acids, in thermophilic cyanobacteria Mastigocladus laminosus and Tolypothrix sp.

Reversed phase liquid chromatography–atmospheric pressure chemical ionization mass spectrometry (RP-HPLC/APCI-MS) was used for direct analysis of triacylglycerols (TAGs) from different strains of the cyanobacteria Mastigocladus laminosus, Tolypothrix cf. tenuis and Tolypothrix distorta. This technique enabled us to identify and quantify the specific molecular species of TAGs directly from lipid extracts of the cyanobacteria. The regioisomeric series of TAGs having α-linolenic and γ-linolenic and also oleic and cis-vaccenic acids were separated by RP-HPLC and identified by APCI-MS. M. laminosus produced only a few molecular species of TAGs, including both isomers of octadecenoic (oleic and vaccenic) acid, while T. distorta contained tens of molecular species of TAGs having FAs with up to four double bonds (stearidonic acid and including also its positional isomer, i.e. 3,6,9,12-octadecatetraenoic acid) and both positional isomers (α and γ) of linolenic acids. Individual strains of both cyanobacteria exhibited different contents of polyunsaturated fatty acids (Tolypothrix sp.) and different distribution of positional isomers of monoenoic fatty acids in TAGs (M. laminosus).

Development of a novel direct-infusion atmospheric pressure chemical ionization mass spectrometry method for the analysis of heavy hydrocarbons in light shredder waste

A novel direct-infusion atmospheric pressure chemical ionization mass spectrometry method to identify saturated straight-chain hydrocarbons in light shredder waste fraction has been developed. Ionization of alkanes under nitrogen gas source favored hydrogen abstraction producing mostly (M–H)+ ions, which strictly correspond to their respective series of n-alkanes between n-decane (C10) and n-tetra-contane (C40). The method is shown to produce intact gas phase ions of n-alkane in both reference and real life waste samples. APCI-MS2 fragmentation data assisted in the structural verification of the n-alkanes investigated in both standard and waste mixtures.

Analysis of secondary organic aerosols in air using extractive electrospray ionization mass spectrometry (EESI-MS)

Extractive electrospray ionization mass spectrometry (EESI-MS) has been shown, in other laboratories, to be a useful technique for the analysis of aerosols from a variety of sources. EESI-MS is applied here, for the first time, to the analysis of secondary organic aerosol (SOA) formed from the reaction of ozone and α-pinene. The results are compared to those obtained using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The SOA was generated in the laboratory and merged with electrospray droplets. The recovered ions were directed towards the inlet of a triple quadrupole mass spectrometer. Through the use of a denuder to remove gas phase compounds, the EESI-MS technique was found to be effective for measuring the major ozonolysis products either in particles alone or in a combination of vapor phase and particulate products. Due to its relatively simple setup and the avoidance of sample collection and work-up, EESI-MS shows promise as an excellent tool for the characterization of atmospherically relevant particles.

A tandem mass spectrometric study of bile acids: Interpretation of fragmentation pathways and differentiation of steroid isomers

Bile acids are steroids with a pentanoic acid substituent at C-17. They are the terminal products of cholesterol excretion, and play critical physiological roles in human and animals. Bile acids are easy to detect but difficult to identify by using mass spectrometry due to their poly-ring structure and various hydroxylation patterns. In this study, fragmentation pathways of 18 free and conjugated bile acids were interpreted by using tandem mass spectrometry. The analyses were conducted on ion trap and triple quadrupole mass spectrometers. Upon collision-induced dissociation, the conjugated bile acids could cleave into glycine or taurine related fragments, together with the steroid skeleton. Fragmentations of free bile acids were further elucidated, especially by atmospheric pressure chemical ionization mass spectrometry in positive ion mode. Aside from universally observed neutral losses, eliminations occurred on bile acid carbon rings were proposed for the first time. Moreover, four isomeric 5β-cholanic acid hydroxyl derivatives (3α,6α-, 3α,7β-, 3α,7α-, and 3α,12α-) were differentiated using electrospray ionization in negative ion mode: 3α,7β-OH substituent inclined to eliminate H 2O and CH 2O 2 groups; 3α,6α-OH substituent preferred neutral loss of two H 2O molecules; 3α,12α-OH substituent apt to lose the carboxyl in the form of CO 2 molecule; and 3α,7α-OH substituent exhibited no further fragmentation after dehydration. This study provided specific interpretation for mass spectra of bile acids. The results could contribute to bile acid analyses, especially in clinical assays and metabonomic studies.