Showing papers on "Atmospheric-pressure chemical ionization published in 2010"

Ambient Ionization Mass Spectrometry

Abstract: Mass spectrometric ionization methods that operate under ambient conditions and require minimal or no sample pretreatment have attracted much attention in such fields as biomedicine, food safety, antiterrorism, pharmaceuticals, and environmental pollution. These technologies usually involve separate ionization and sample-introduction events, allowing independent control over each set of conditions. Ionization is typically performed under ambient conditions through use of existing electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) techniques. Rapid analyses of gas, liquid, and solid samples are possible with the adoption of various sample-introduction methods. This review sorts different ambient ionization techniques into two main subcategories, primarily on the basis of the ionization processes, that are further differentiated in terms of the approach used for sampling.

Development of a candidate reference measurement procedure for the determination of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in human serum using isotope-dilution liquid chromatography-tandem mass spectrometry

Abstract: Vitamin D exists in two major forms, vitamin D3 and vitamin D2. Vitamin D helps the body absorb calcium and promote optimal bone health. Both forms of vitamin D are metabolized to 25-hydroxyvitamin D in the body, and the levels of 25-hydroxyvitamin D3 [25(OH)D3] and 25-hydroxyvitamin D2 [25(OH)D2] in serum are considered the best indicators of vitamin D status. A candidate reference measurement procedure for serum 25(OH)D3 and 25(OH)D2 has been developed and critically evaluated. The deuterated compounds 25(OH)D3-d3 and 25(OH)D2-d3 are used as internal standards for 25(OH)D3 and 25(OH)D2, respectively. The 25(OH)D3 and 25(OH)D2 and their respective labeled internal standards are simultaneously extracted from serum using liquid−liquid extraction prior to reversed-phase liquid chromatography−tandem mass spectrometry (LC−MS/MS). Chromatographic separation was performed using a cyano (CN) column for both 25(OH)D3 and 25(OH)D2. Atmospheric pressure chemical ionization (APCI) in the positive ion mode and multip...

Electrospray and MALDI Mass Spectrometry: Fundamentals, Instrumentation, Practicalities, and Biological Applications

Abstract: Foreword: Desorption Ionization and Spray Ionization: Connections and Progress ( R. Graham Cooks). Foreword to the First Edition (John B. Fenn). Preface (Richard B. Cole). Contributors. Part I Fundamentals of ES. 1. On the Mechanism of Electrospray Ionization Mass Spectrometry (ESIMS) (Paul Kebarle and Udo H. Verkerk). 2. Selectivity in Electrospray Ionization Mass Spectrometry (Nadja B. Cech and Christie G. Enke). 3. Electrochemistry of the Electrospray Ion Source (Gary J. Van Berkel and Vilmos Kertesz). 4. ESI Source Design (Andries P. Bruins). Part II Fundamentals of MALDI. 5. MALDI Ionization Mechanisms: an Overview (Richard Knochenmuss). 6. The Development of Matrix-Assisted Laser Desorption/Ionization Sources (Peter B. O'Connor). 7. A Comparison of MALDI Matrices (Mahmud Hossain and Patrick A. Limbach). 8. MALDI Imaging Mass Spectrometry (Alain Brunelle and Olivier Laprevote). Part III ES and MALDI Coupling to Mass Spectrometry Instrumentation. 9. Coupling ESI and MALDI Sources to the Quadrupole Mass Filter, Quadrupole Ion Trap, Linear Quadrupole Ion Trap, and Orbitrap Mass Analyzers (Mark E. Bier). 10. Time-of-Flight Mass Spectrometry (Robert J. Cotter). 11. Fourier Transform Ion Cyclotron Resonance and Magnetic Sector Analyzers for ESI and MALDI (Jeremy J. Wolff and I. Jonathan Amster). 12. Ion Mobility Mass Spectrometry (John A. McLean, J. Albert Schultz, and Amina S. Woods). Part IV Practical Aspects of ES and MALDI. 13. ESI, APCI, and MALDI A Comparison of the Central Analytical Figures of Merit: Sensitivity, Reproducibility, and Speed (Thomas R. Covey, Bradley B. Schneider, Hassan Javaheri, J.C. Yves LeBlanc, Gordana Ivosev, Jay J. Corr, and Peter Kovarik). 14. Charge State Distributions in Electrospray and MALDI (Yan Li and Richard B. Cole). 15. Probing Noncovalent Interactions by Electrospray Ionization and Matrix-Assisted Laser Desorption/Ionization (Sonal Mathur, Alexis Nazabal, and Renato Zenobi). 16. Ion Activation Methods for Tandem Mass Spectrometry (Kristina H&aakansson and John S. Klassen). 17. Dissociation of Even-Electron Ions (Carlos Afonso, Richard B. Cole, and Jean-Claude Tabet). Part V Biological Applications of ES and MALDI. 18. The Role of Mass Spectrometry for Peptide, Protein, and Proteome Characterization (A. Jimmy Ytterberg, Jason Dunsmore, Shirley H. Lomeli, Mario Thevis, Yongming Xie, Rachel R. Ogorzalek Loo, and Joseph A. Loo). 19. Carbohydrate Analysis by ESI and MALDI (David J. Harvey). 20. Applications of ESI and MALDI to Lipid Analysis (Xianlin Han). 21. In Vitro ADME Profiling and Pharmacokinetic Screening in Drug Discovery (Daniel B. Kassel). Index.

Athabasca oil sands process water: characterization by atmospheric pressure photoionization and electrospray ionization fourier transform ion cyclotron resonance mass spectrometry.

Abstract: The Athabasca oil sands in Canada are a less conventional source of oil which have seen rapid development. There are concerns about the environmental impact, with particular respect to components in oil sands process water which may enter the aquatic ecosystem. Naphthenic acids have been previously targeted for study, due to their implications in toxicity toward aquatic wildlife, but it is believed that other components, too, contribute toward the potential toxicity of the oil sands process water. When mass spectrometry is used, it is necessary to use instrumentation with a high resolving power and mass accuracy when studying complex mixtures, but the technique has previously been hindered by the range of compounds that have been accessible via common ionization techniques, such as electrospray ionization. The research described here applied Fourier transform ion cyclotron resonance mass spectrometry in conjunction with electrospray ionization and atmospheric pressure photoionization, in both positive-ion...

Ion suppression and enhancement effects of co‐eluting analytes in multi‐analyte approaches: systematic investigation using ultra‐high‐performance liquid chromatography/mass spectrometry with atmospheric‐pressure chemical ionization or electrospray ionization

Abstract: In multi-analyte procedures, sufficient separation is important to avoid interferences, particularly when using liquid chromatography/mass spectrometry (LC/MS) because of possible ion suppression or enhancement. However, even using ultra-high-performance LC, baseline separation is not always possible. For development and validation of an LC/MS/MS approach for quantification of 140 antidepressants, benzodiazepines, neuroleptics, beta-blockers, oral antidiabetics, and analytes measured in the context of brain death diagnosis in plasma, the extent of ion suppression or enhancement of co-eluting analytes within and between the drug classes was investigated using atmospheric-pressure chemical ionization (APCI) or electrospray ionization (ESI). Within the drug classes, five analytes showed ion enhancement of over 25% and six analytes ion suppression of over 25% using APCI and 16 analytes ion suppression of over 25% using ESI. Between the drug classes, two analytes showed ion suppression of over 25% using APCI. Using ESI, one analyte showed ion enhancement of over 25% and five analytes ion suppression of over 25%. These effects may influence the drug quantification using calibrators made in presence of overlapping and thus interfering analytes. Ion suppression/enhancement effects induced by co-eluting drugs of different classes present in the patient sample may also lead to false measurements using class-specific calibrators made in absence of overlapping and thus interfering analytes. In conclusion, ion suppression and enhancement tests are essential during method development and validation in LC/MS/MS multi-analyte procedures, with special regards to co-eluting analytes.

Shotgun lipidomic analysis of human meibomian gland secretions with electrospray ionization tandem mass spectrometry.

Abstract: Lipids secreted from the meibomian glands (meibum) form the outmost layer of tear film covering the ocular surface. A primary function of this superficial lipid layer is to prevent evaporation of the aqueous component in the tear film.1 Changes in lipid profiles of meibum likely lead to ocular surface diseases such as dry eye disease, which is a prevalent condition affecting over 12 million Americans, or 6% to 27% of people worldwide.2 Therefore, it is important to know the identities of the components in meibum to better diagnose and manage ocular surface disease, with the additional goal of future therapeutic development. The conventional methods applied to the analysis of meibum samples include thin layer chromatography (TLC), nuclear magnetic resonance spectroscopy, gas chromatography (GC), and gas chromatography-mass spectrometry (GC-MS).3 With these methods, progress has been made in identifying the lipid components in meibum. Previously, the major components of meibum have been reported to be wax esters (WEs),4–8 cholesteryl esters (CEs),4–8 diesters (DEs),4,5,7 and triacylglycerols (TGs).4–8 The major fatty acid and fatty alcohol moieties of these lipids have also been determined.7,9 However, limitations still exist with these methods, including low sensitivity, low resolution, possible degradation due to prolonged exposure time, low sample recovery due to derivatization, isomerization, and/or decomposition due to sustained high temperature analysis and long analysis time.3 Furthermore, these methods are mainly based on hydrolysis and derivatization followed by GC-MS analysis of all the meibum lipids or a certain subclasses; thus information of the fatty acid or fatty alcohol moieties only has been obtained and the more important qualitative and quantitative information of individual intact lipids was missing. To circumvent these limitations, atmospheric pressure chemical ionization (APCI)-MS coupled with reversed-phase or normal phase high-performance liquid chromatography (HPLC) separation was recently applied for the direct analysis of the meibum lipids including WEs10,11 and CEs12 without derivatization. However, the high energy and the high temperature involved with APCI could cause the dissociation of some lipid species. For instance, saturated CE peaks are spontaneously fragmented with APCI-MS.12 This creates a challenge in providing accurate identification and quantitation. In addition, a large number of samples are required for APCI-MS analysis because only high flow rate (>0.2 mL/min) is compatible with this method. In contrast, electrospray ionization (ESI) is a “softer” ionization method13 and can be operated at low flow rate; thus it is more compatible for the analysis of unstable lipids as well as limited or small volume samples. The application of ESI-MS to meibum samples has been reported recently.11,14,15 In this work, direct ESI-MS and MS/MS analyses were performed for individual meibum samples collected by capillary tube after meibomian gland expression. After minimizing the interference peaks and increasing the signal-to-noise ratio, we confirmed the previously reported major lipid species, including WEs, CEs, DEs, TGs, and free fatty acids (FFAs) in meibum samples. More importantly, we also determined the major molecular components of these lipid species. To the best of our knowledge, this is the most detailed report of the major species in meibum on the molecular level. Furthermore, we also observed a set of peaks reported recently as those of (O-acyl)-ω-hydroxy fatty acids (OAHFAs).16 These OAHFAs may play important role in maintaining the stability of tear film.

Molecular Structures of Asphaltenes Based on the Dissociation Reactions of Their Ions in Mass Spectrometry

Abstract: We report here an examination of the mass spectrometric fragmentation behavior of molecular ions generated (and excited) by electron ionization (EI) from several asphaltene model compounds simulating both the island and archipelago structural models. This behavior is compared to that of protonated molecules generated from the same compounds by atmospheric pressure chemical ionization (APCI) and excited by collision-activated dissociation (CAD). The fragmentation behavior of the protonated molecules and molecular ions is surprisingly similar. Both types of ions yielded distinct fragmentation patterns for both types of model compounds. Ions derived from the island-type model compounds fragment predominantly by losing their alkyl chains (with either all carbons or all but one), one after another, which allows for the identification of the chain lengths and counting the number of chains. Increasing the length of the alkyl chains reduces the extent of spontaneous fragmentation occurring upon EI, likely because...

Systematic investigation of ion suppression and enhancement effects of fourteen stable‐isotope‐labeled internal standards by their native analogues using atmospheric‐pressure chemical ionization and electrospray ionization and the relevance for multi‐analyte liquid chromatographic/mass spectrometric procedures

Abstract: In clinical and forensic toxicology, multi-analyte procedures are very useful to quantify drugs and poisons of different classes in one run. For liquid chromatographic/tandem mass spectrometric (LC/MS/MS) multi-analyte procedures, often only a limited number of stable-isotope-labeled internal standards (SIL-ISs) are available. If an SIL-IS is used for quantification of other analytes, it must be excluded that the co-eluting native analyte influences its ionization. Therefore, the effect of ion suppression and enhancement of fourteen SIL-ISs caused by their native analogues has been studied. It could be shown that the native analyte concentration influenced the extent of ion suppression and enhancement effects leading to more suppression with increasing analyte concentration especially when electrospray ionization (ESI) was used. Using atmospheric-pressure chemical ionization (APCI), methanolic solution showed mainly enhancement effects, whereas no ion suppression and enhancement effect, with one exception, occurred when plasma extracts were used under these conditions. Such differences were not observed using ESI. With ESI, eleven SIL-ISs showed relevant suppression effects, but only one analyte showed suppression effects when APCI was used. The presented study showed that ion suppression and enhancement tests using matrix-based samples of different sources are essential for the selection of ISs, particularly if used for several analytes to avoid incorrect quantification. In conclusion, only SIL-ISs should be selected for which no suppression and enhancement effects can be observed. If not enough ISs are free of ionization interferences, a different ionization technique should be considered. Copyright © 2010 John Wiley & Sons, Ltd.

Potential of atmospheric pressure chemical ionization source in GC-QTOF MS for pesticide residue analysis.

Abstract: The potential applications of a new atmospheric pressure source for GC-MS analysis have been investigated in this work. A list of around 100 GC-amenable pesticides, which includes organochlorine, organophosphorus and organonitrogenated compounds, has been used to evaluate their behavior in the new source. Favoring the major formation of the molecular ion in the source has been the main goal due to the wide-scope screening possibilities that this fact brings in comparison with the traditional, highly fragmented electron ionization spectra. Thus, the addition of water as modifier has been tested as a way to promote the generation of protonated molecules. Pesticides investigated have been classified into six groups according to their ionization/fragmentation behavior. Four of them are characterized by the abundant formation of the protonated molecule in the atmospheric pressure source, mostly being the base peak of the spectrum. These results show that wide-scope screening could be easily performed with this source by investigating the presence of the protonated molecule ion, MH+. The developed procedure has been applied to pesticide screening in different food samples (nectarine, orange and spinach) and it has allowed the presence of several pesticides to be confirmed such as chlorpyriphos ethyl, deltamethrin and endosulfan sulfate. The availability of a quadrupole time-of-flight instrument made it feasible to perform additional MS/MS experiments for both standards and samples to go further in the confirmation of the identity of the detected compounds. Results shown in this paper have been obtained using a prototype source which exhibits promising features that could be applied to other analytical problems apart from those illustrated in this work.

Integrated Ionization Approach for RRLC−MS/MS-based Metabonomics: Finding Potential Biomarkers for Lung Cancer

Abstract: An integrated ionization approach of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) combining with rapid resolution liquid chromatography mass spectrometry (RRLC-MS) has been developed for performing global metabonomic analysis on complex biological samples. This approach was designed to overcome the low ionization efficiencies of endogenous metabolites due to diverse physicochemical properties as well as ion suppression, and obtain comprehensive metabolite profiles in LC-MS analysis. Ionization capability and applicability were manifested by improved ionization efficiency and enlarged metabolite coverage in analysis on typical urinary metabolite standards and urine samples from healthy volunteers. The method was validated by the limit of detection and precision. When applied to the global metabonomic studies of lung cancer, more comprehensive biomarker candidates were obtained to reflect metabolic traits between healthy volunteers and lung cancer patients, including 74 potential biomarkers in positive ion mode and 59 in negative ion mode. Taking identical potential biomarkers of any two or three ionization methods into account, analysis using ESI-MS in positive (+) and negative (-) ion mode contributed to 70 and 64% of the total potential biomarkers, respectively. The biomarker discovery capability of (+/-) APCI-MS accounted for 45 and 42% of the overall; meanwhile (+/-) APPI-MS amounted for 39 and 54%. These results indicated that potential biomarkers with vital biological information could be missed if only a single ionization method was used. Furthermore, 11 potential biomarkers were identified including amino acids, nucleosides, and a metabolite of indole. They revealed elevated amino acid and nucleoside metabolism as well as protein degradation in lung cancer patients. This proposed approach provided a more comprehensive picture of the metabolic changes and further verified identical biomarkers that were obtained simultaneously using different ionization methods.

Laser Diode Thermal Desorption/Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometry Analysis of Selected Steroid Hormones in Wastewater: Method Optimization and Application

Abstract: A rapid and reliable method enabling high-throughput sample analysis for quicker data generation, detection, and monitoring of eight selected steroid hormones in water matrixes was developed and validated. Our approach is based on a novel sample introduction method, the laser diode thermal desorption/atmospheric pressure chemical ionization (LDTD/APCI) coupled to tandem mass spectrometry (MS/MS). The optimization of instrumental parameters and a method application are presented. Our method was successfully applied to spiked effluent wastewater in the low-nanogram per liter concentrations with total analysis time reduced to seconds (15 s) using LDTD/APCI-MS/MS compared to minutes with traditional liquid-chromatography coupled to tandem mass spectrometry (LC−MS/MS) following solid-phase extraction (SPE). The instrumental detection limits for LDTD/APCI-MS/MS ranged from 5 to 24 μg L−1 and from 13 to 43 ng L−1 for the method detection limits. Calibration curves in wastewater matrix showed good linearity (R2 >...

Identification of Organic Nitrates in the NO3 Radical Initiated Oxidation of α-Pinene by Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract: The gas-phase reactions of nitrate radicals (NO3) with biogenic organic compounds are a major sink for these organics during night-time. These reactions form secondary organic aerosols, including organic nitrates that can undergo long-range transport, releasing NOx downwind. We report here studies of the reaction of NO3 with α-pinene at 1 atm in dry synthetic air (relative humidity ∼3%) and at 298 K using atmospheric pressure chemical ionization triple quadrupole mass spectrometry (APCI-MS) to identify gaseous and particulate products. The emphasis is on the identification of individual organic nitrates in the particle phase that were obtained by passing the product mixture through a denuder to remove gas-phase reactants and products prior to entering the source region of the mass spectrometer. Filter extracts were also analyzed by GC-MS and by APCI time-of-flight mass spectrometry (APCI-ToF-MS) with methanol as the proton source. In addition to pinonaldehyde and pinonic acid, five organic nitrates were i...

Quantification of triacylglycerol regioisomers by ultra-high-performance liquid chromatography and ammonia negative ion atmospheric pressure chemical ionization tandem mass spectrometry.

Abstract: The regioisomer composition of triacylglycerols (TAGs) in various vegetable oils was determined with a new liquid chromatography/tandem mass spectrometry (LC/MS/MS method). A direct inlet ammonia negative ion chemical ionization (NICI) MS/MS method was improved by adapting it to LC negative ion (NI) atmospheric pressure chemical ionization (APCI) MS/MS system using ammonia as nebulizer gas. The method is based on the preferential formation of [M-H-RCOOH-100](-) ions during collision-induced dissociation by loss of sn-1/3 fatty acids from [M-H](-) ions. Calibration curves were created from nine reference TAGs: Ala/L/L, Gla/L/L, L/L/O, L/O/O, P/O/O, P/P/O, Po/Po/V, Po/Po/O, and C/O/O. The calibration curves were used to quantify the regioisomer compositions of selected TAGs in rapeseed oil, sunflower seed oil, palm oil, black currant seed oil, and sea buckthorn pulp oil. The method discriminates the different regioisomers and the results obtained by this method were in good agreement with previous results. This proves that this new method can be used for the determination of regiospecific distribution of fatty acids in TAGs.

Development of liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry for analysis of halogenated flame retardants in wastewater

Abstract: Until recently, atmospheric pressure photoionization (APPI) has typically been used for the determination of non-polar halogenated flame retardants (HFRs) by liquid chromatography (LC) tandem mass spectrometry. In this study, we demonstrated the feasibility of utilizing liquid chromatography atmospheric pressure chemical ionization (APCI) tandem mass spectrometry (LC-APCI-MS/MS) for analysis of 38 HFRs. This developed method offered three advantages: simplicity, rapidity, and high sensitivity. Compared with APPI, APCI does not require a UV lamp and a dopant reagent to assist atmospheric pressure ionization. All the isomers and the isobaric compounds were well resolved within 14-min LC separation time. Excellent instrument detection limits (6.1 pg on average with 2.0 μL injection) were observed. The APCI mechanism was also investigated. The method developed has been applied to the screening of wastewater samples for screening purpose, with concentrations determined by LC-APCI-MS/MS agreeing with data obtained via gas chromatography high resolution mass spectrometry.

Simultaneous determination by ultra-performance liquid chromatography–atmospheric pressure chemical ionization time-of-flight mass spectrometry of nitrated and oxygenated PAHs found in air and soot particles

Abstract: An ultra-performance liquid chromatographic-atmospheric pressure chemical ionization time-of-flight mass spectrometric (UPLC-APCIToFMS) method for rapid analysis of twelve nitrated polycyclic aromatic hydrocarbons (NPAHs) and nine oxygenated polycyclic aromatic hydrocarbons (OPAHs) in particle samples has been developed. The extraction step using pressurized liquid extraction was optimized by experimental design methods and the concentrated extracts were analyzed without further clean-up. Matrix effects resulting in suppression or enhancement of the response during the ionization step were not observed. The suitability of the developed method is demonstrated by analysis of six different particle samples including standard reference materials, atmospheric particles collected by a high-volume sampler at an urban background site, and a soot sample from a burner. Results from these measurements showed clear differences between the different kinds of samples. Concentrations from reference materials are in good agreement with those from previous studies. Additionally a clear seasonal trend could be observed in atmospheric NPAH and OPAH concentrations found in real samples, with higher concentrations in winter.

High-throughput quantitation of seven sulfonamide residues in dairy milk using laser diode thermal desorption-negative mode atmospheric pressure chemical ionization tandem mass spectrometry.

Abstract: Sulfonamides are antibiotic compounds widely used in the dairy industry. Their presence in diary milk poses a risk to public health and may also contribute to the spread of antibiotic resistance in bacteria. Sulfonamide residues in dairy milk were quantified by tandem mass spectrometry (MS/MS) using a novel ionization source based on laser diode thermal desorption-negative mode atmospheric pressure chemical ionization (LDTD-APCI(-)). Seven sulfonamides spiked in milk were extracted with acetonitrile, which yielded high recoveries (77.5-101.5%). Calibration curves in the matrix showed good linearity (0.9977 >or= R(2) >or= 0.9658) over the dynamic range (1.6-500 microg L(-1)), and limits of quantitation were between 2 and 14 microg L(-1), lower than or of the same magnitude as maximum residue criteria set by several regulatory agencies (10-100 ng L(-1)). In addition, the run time using the LDTD-MS/MS system was 30 s per sample, as compared to actual methods running from 7 to 84 min for the same sulfonamide residue compounds, which gave the method the high screening throughput capacity necessary for monitoring milk production.

Soluble Chlorofullerenes C60Cl2,4,6,8,10. Synthesis, Purification, Compositional Analysis, Stability, and Experimental/Theoretical Structure Elucidation, Including the X-ray Structure of C1-C60Cl10

Abstract: The efficacy of various analytical techniques for the characterization of products of C60 chlorination reactions were evaluated by (i) using samples of C60Cl6 of known purity and (ii) repeating a number of literature syntheses reported to yield pure C60Cln compounds The techniques were NMR, UV−vis, IR, and Raman spectroscopy, FAB, MALDI, LDI, ESI, and APCI mass spectrometry, HPLC, TGA, elemental analysis, and single-crystal X-ray diffraction Most of these techniques are shown to give ambiguous or erroneous results, calling into question the composition and/or purity of nearly all C60Cln compounds reported to date The optimum analytical method for chlorofullerenes was found to be a combination of HPLC and either MALDI or APCI mass spectrometry For the first time, the chlorination of C60 by ICl, ICl3, and Cl2 was studied in detail using dynamic HPLC analysis and APCI mass spectrometry Suitable conditions were found for the preparation of the new chlorofullerenes 1,7-C60Cl2, 1,9-C60Cl2, 1,6,9,18-C60Cl4,