Analytical and Bioanalytical Chemistry (v.406, #25)
ABC Spotlight on carbon nanotubes (CNTs) by Günter Gauglitz (6077-6079).
is Senior Professor at the Eberhard-Karls-University of Tübingen working in analytical and physical chemistry. He was chairman of the GDCh Division of Analytical Chemistry and chaired the Europt(r)ode VIII meeting. For more than 15 years his main scientific interests have centered on research and development in chemical and biochemical sensors with special focus on the characterization of interfaces of polymers and biomembrane surfaces, spectroscopic techniques, use of spectral interferometry to monitor changes in optical thickness of thin layers, and effects of Fresnel reflectivity at interfaces. He has been Editor of Analytical and Bioanalytical Chemistry (ABC) since 2002.
Letter to the Editor regarding “Pitfalls in quality assurance” by Jens E. T. Andersen (6081-6082).
Yukihiro Ozaki, Katrin Kneipp, Ricardo Aroca (Eds.): Frontiers of surface-enhanced Raman scattering: single nanoparticles to single cells by Zachary D. Schultz (6083-6084).
Gwen O’Sullivan and Court Sandau (Eds.): Environmental forensics for persistent organic pollutants by Ethel Eljarrat (6085-6086).
Size-exclusion chromatography—from high-performance to ultra-performance by Elena Uliyanchenko (6087-6094).
Size-exclusion chromatography (SEC) enables measurement of the average molecular weights and molecular-weight distributions of polymers. Because these characteristics may, in turn, be correlated with important performance characteristics of plastics, SEC is an essential analytical technique for characterization of macromolecules. Although SEC is one of the oldest instrumental chromatographic techniques, it is still under continuous development, as a result of the great demand for increased resolution and faster analysis in SEC. Ultra-high-pressure size-exclusion chromatography (UHPSEC) was recently introduced to satisfy the growing demands of analytical chemists. Using instrumentation capable of generating very high pressures and columns packed with small particles, this technique enables greater separation efficiency and faster analysis than are achieved with conventional SEC. UHPSEC is especially advantageous for high-resolution analysis of oligomers, for very rapid polymer separations, and as a second dimension in comprehensive two-dimensional liquid chromatography of polymers. In this paper we discuss the benefits of UHPSEC for separation of macromolecules, with examples from the literature.
Keywords: Size-exclusion chromatography; Ultra-high-pressure liquid chromatography; Advanced polymer chromatography; Rapid polymer separations; High-resolution oligomer separations; Two-dimensional liquid chromatography
Liquid chromatographic enantiomer separation with special focus on zwitterionic chiral ion-exchangers by Michael Lämmerhofer (6095-6103).
This article provides a condensed introduction to principles of chiral separation, gives a historic overview of the genesis of the most important concepts regarding chiral stationary phase (CSPs), and summarizes the state of the art in a concise manner. Some recent developments in the field of polysaccharide CSPs are outlined. Finally, the article focusses on the new concept of zwitterionic chiral stationary phases and their application profile and peculiarities. Some other trends in column technology, including sub-2 μm and core–shell CSP particles and the emerging field of (UP)SFC, are briefly discussed. Figure ᅟ
Keywords: Chiral separation; Enantioselective (U)HPLC and SFC; Chiral stationary phase; Cinchona alkaloid; Quinine and quinidine carbamates; Amino acids
Trends in analyzing emerging drugs of abuse – from seized samples to body samples by Markus R. Meyer (6105-6110).
This article summarizes the current status of and new trends of analytical approaches in the field of forensic/clinical toxicology for analyzing emerging drugs of abuse. Instruments and devices used for compound identification will be presented as well as types of biosample used to check for drug intake. Finally, a new and promising strategy will be presented, which allows to monitor the consumption of emerging drugs of abuse without using real body samples.
Keywords: Drugs of abuse; Toxicology; NPS; Identification
Plasma-based ambient desorption/ionization mass spectrometry: state-of-the-art in qualitative and quantitative analysis by Anastasia Albert; Jacob T. Shelley; Carsten Engelhard (6111-6127).
Ambient desorption/ionization mass spectrometry (ADI-MS) aims to enable direct analysis of gaseous, liquid, and/or solid samples under ambient conditions. In ADI-MS, different types of desorption/ionization sources are classified according to their basic method of operation, namely spray-based, laser-based, or plasma-based. This review discusses many of the plasma-based techniques coupled to mass spectrometry in terms of their current performance in fast qualitative screening and quantitative analysis. Critical aspects, for example sample preparation and introduction, quantification, and matrix effects, are addressed. Furthermore, the applicability of plasma-based sources to portable mass spectrometers and their capabilities in imaging experiments are summarized. The applications discussed are of two types. In one, direct screening is performed without any or with minimal sample pretreatment. Samples with low matrix content are qualitatively analyzed without interferences. The other, more challenging applications, namely samples with high matrix content and most quantitative analysis, typically require sample preparation ranging from simple dilution to extensive multi-step procedures. Fig ᅟ
Keywords: Ambient desorption/ionization mass spectrometry; Plasma-based ion sources; State-of-the-art; Critical review; Fast screening; Quantitative analysis
Progress in stacking techniques based on field amplification of capillary electrophoresis by Dong-Sheng Lian; Shu-Jin Zhao; Jian Li; Bing-Ling Li (6129-6150).
Numerous strategies have been developed to mitigate the intrinsic low detection sensitivity that is a limitation of capillary electrophoresis. Among them, in-line stacking is an effective strategy to address the sensitivity challenge, and among the different stacking techniques, stacking based on field amplification is the most effective and simplest method of achieving high sensitivity without special complicated mechanisms or operations. This review introduces several stacking techniques based on field amplification. Field-amplified sample stacking, large-volume sample stacking, matrix field-amplified stacking injection (FASI), head-column FASI, matrix FASI combined with head-column FASI, FASI coupled with extraction and clean-up methods, electrokinetic supercharging, cation–anion selective exhaustive injection-sweeping-micellar electrokinetic chromatography, and newly developed techniques based on field amplification combined with other methods are included, and examples of straightforward methods for solving the sensitivity problem are provided. We also present a brief overview of the advantages, limitations, and future developments of these techniques. Graphical Abstract ᅟ
Keywords: Field amplification; Stacking; Pre-concentration; Sensitivity
Analytical approaches for the determination of PCB metabolites in blood: a review by Natalia Quinete; Thomas Schettgen; Jens Bertram; Thomas Kraus (6151-6164).
Polychlorinated biphenyls (PCBs) are among the most ubiquitous pollutants in the environment, and their metabolism leads to the formation of hydroxylated PCBs (OH-PCBs) and methyl sulfone PCBs (MeSO2-PCBs). These metabolites are generally more hydrophilic than the parent compound, and therefore are more easily eliminated from the body. However, some congeners have been shown to be strongly retained in human blood, binding to transthyretin with an affinity that is, in general, greater than that of the natural ligand thyroxin itself, which could result in toxicological effects, particularly on the thyroid system. Currently available analytical methods require, in general, extensive sample preparation, which includes a series of time-consuming and low-throughput liquid–liquid and back extractions, evaporations, several cleanup steps, and in some cases, derivatization prior to analysis by gas chromatography (GC) or liquid chromatography (LC) coupled with mass spectrometry (MS). Recent developments in the use of LC coupled with tandem MS (MS/MS) have brought some improvements in terms of sample preparation for the determination of PCB metabolites in blood, although there are still possibilities for continued development. The selected literature has evidenced few studies of LC–MS/MS-based methods, a lack of analytical standards, nonassessment of lower-chlorinated OH-PCBs, and scarce attention to MeSO2-PCBs in blood. This review aims to evaluate critically the currently available analytical methods for determination of OH-PCBs and MeSO2-PCBs in blood.
Keywords: Analytical methods; Hydroxylated PCBs; Methyl sulfone PCBs; Liquid chromatography–tandem mass spectrometry; Gas chromatography–tandem mass spectrometry; Endocrine disruptor
Detection of potentially skin sensitizing hydroperoxides of linalool in fragranced products by Susanne Kern; Hafida Dkhil; Prisca Hendarsa; Graham Ellis; Andreas Natsch (6165-6178).
is a research scientist in the analytical chemistry department at Givaudan Fragrance S+T. She has a PhD degree in environmental analytical chemistry from Eawag/Swiss Federal Institute of Technology. is an analytical chemist in the perfume analysis department at Givaudan France. She has a master’s degree in organic spectrochemistry analysis and physical chemistry from Pierre and Marie Curie University. was a perfume analyst trainee in the perfume analysis department at Givaudan France. She has a master’s degree in analytical chemistry and theoretical physics from Pierre and Marie Curie University. studied chemistry at the University of Wales, Cardiff, and toxicology at Birmingham University in the UK. He is now Head of Global Toxicology for the fragrance division at Givaudan and is responsible for regulatory affairs and product safety for Europe, the Middle East and Africa, with a specific focus on fragrance allergy. His recent research focus has been on the development and use of exposure data in risk assessment for fragrances, further developing the quantitative risk assessment tool for sensitization. studied at the Swiss Federal Institute of Technology and received his PhD degree in environmental microbiology. His current focus is on developing and implementing in vitro assays to study toxicological risks associated with cosmetic and fragrance ingredients without using animal testing. On prolonged exposure to air, linalool can form sensitizing hydroperoxides. Positive hydroperoxide patch tests in dermatitis patients have frequently been reported, but their relevance has not been established. Owing to a lack of analytical methods and data, it is unclear from which sources the public might be exposed to sufficient quantities of hydroperoxides for induction of sensitization to occur. To address this knowledge gap, we developed analytical methods and performed stability studies for fine fragrances and deodorants/antiperspirants. In parallel, products recalled from consumers were analysed to investigate exposure to products used in everyday life. Liquid chromatography–mass spectrometry with high mass resolution was found to be optimal for the selective and sensitive detection of the organic hydroperoxide in the complex product matrix. Linalool hydroperoxide was detected in natural linalool, but the amount was not elevated by storage in a perfume formulation exposed to air. No indication of hydroperoxide formation in fine fragrances was found in stability studies. Aged fine fragrances recalled from consumers contained a geometric mean linalool concentration of 1,888 μg/g and, corrected for matrix effects, linalool hydroperoxide at a concentration of around 14 μg/g. In antiperspirants, we detected no oxidation products. In conclusion, very low levels of linalool hydroperoxide in fragranced products may originate from raw materials, but we found no evidence for oxidation during storage of products. The levels detected are orders of magnitude below the levels inducing sensitization in experimental animals, and these results therefore do not substantiate a causal link between potential hydroperoxide formation in cosmetics and positive results of patch tests. Graphical Abstract Formation of hydroperoxides from linalool and detection by LC-MS with high resolution
Keywords: Skin sensitization; Allergy; Hydroperoxides; High-resolution mass spectrometry; Fragrance; Linalool
Evaluation of sphingomyelin, cholester, and phosphatidylcholine-based immobilized artificial membrane liquid chromatography to predict drug penetration across the blood-brain barrier by Mike De Vrieze; Dieter Verzele; Roman Szucs; Pat Sandra; Frédéric Lynen (6179-6188).
is doctoral researcher at the Separation Science Group at the Department of Organic and Macromolecular Chemistry in the Faculty of Sciences of Ghent University. His work is focused around testing and developing methods for the prediction of drug penetration across the blood-brain barrier is currently a post-doctoral team leader in medicinal chemistry in the department of pharmaceutical sciences at the University of Antwerp. During his post-doctoral research at the Pfizer Analytical Research Center at Ghent University, he developed advanced sphingomyelin based stationary phases for immobilized artificial membrane (IAM) chromatography. is currently a Senior Research Fellow at Pfizer (Sandwich, UK). The development and implementation of separation methods and technologies to the Full-Development portfolio continues to be his primary interest. He is Chair of the Science Implementation Panel for the Pfizer Analytical Research Center program, which includes the Universities of Ghent (Belgium) and Tasmania (Australia). Roman is a visiting Professor at the University of Ghent, Belgium and Adjunct Professor at Dublin City University, Republic of Ireland. is director of the Research Institute for Chromatography (RIC), Kortijk, Belgium, Emeritus Professor in Separation Science at Ghent University, Belgium, and director of the Pfizer Analytical Research Center-UGent, Belgium. Pat is author or co-author of more than 500 scientific papers, and is a visiting Professor at the University of Evora (Portugal) and at the University of Stellenbosch (South Africa). He is active in all fields of separation sciences (GC, LC, SFC, and CE), and major areas of his research are high-throughput, high-resolution, miniaturization, hyphenation, and automation to study chemicals, pharmaceuticals, natural products, and pollution. is Associate Professor at Ghent University (Belgium), where he is in charge of the Separation Science Group. He is author or co-author of over 80 scientific papers and organizer of the international conference of hyphenated techniques in chromatography. His research interests comprise the development of approaches to increase peak capacities in separation sciences, reaching the attomole range sensitivities via innovative detection and sample preparation strategies, stationary phase synthesis, green chromatography, advanced macro- and biomolecular separations, electrochromatography, high temperature LC, SFC, and nontargeted metabolomics projects. Over the past decades, several in vitro methods have been tested for their ability to predict drug penetration across the blood-brain barrier. So far, in high-performance liquid chromatography, most attention has been paid to micellar liquid chromatography and immobilized artificial membrane (IAM) LC. IAMLC has been described as a viable approach, since the stationary phase emulates the lipid environment of a cell membrane. However, research in IAMLC has almost exclusively been limited to phosphatidylcholine (PC)-based stationary phases, even though PC is only one of the lipids present in cell membranes. In this article, sphingomyelin and cholester stationary phases have been tested for the first time towards their ability to predict drug penetration across the blood-brain barrier. Upon comparison with the PC stationary phase, the sphingomyelin- and cholester-based columns depict similar predictive performance. Combining data from the different stationary phases did not lead to improvements of the models. Figure Schematic representation of how IAM-LC is used to predict drug penetration across the blood-brain barrier.
Keywords: Blood-brain barrier; Liquid chromatography; Immobilized artificial membrane; Phosphatidylcholine; Sphingomyelin; Cholester
Solid-phase extraction and field-amplified sample injection–capillary zone electrophoresis for the analysis of benzophenone UV filters in environmental water samples by Miquel Purrà; Roser Cinca; Jessica Legaz; Oscar Núñez (6189-6202).
has a degree in chemistry (2013) from the Universitat de Barcelona (UB) and did his final degree project at the Department of Analytical Chemistry (UB) under the supervision of Dr. O. Núñez. He is currently a product development scientist in a cosmetics company and studying for a master’s degree in fine chemicals experimentation at the Universitat Autònoma de Barcelona (UAB). has a degree in chemistry (2014) from the Universitat de Barcelona (UB) and did her final degree project at the Department of Analytical Chemistry (UB) under the supervision of Dr. O. Núñez. She is currently a product development scientist in an antifouling paints company and studying for a master’s degree in research, development and control of drugs at the Universitat de Barcelona. has a degree in chemistry (2014) from Universitat de Barcelona (UB) and did her final degree project at the Department of Analytical Chemistry under the supervision of Dr. O. Núñez. She is currently a product development scientist in a cosmetics company and studying for a degree in business administration and management at the Universitat Oberta de Catalunya (UOC). is an associate professor working in the chromatography, capillary electrophoresis and mass spectrometry group at the Department of Analytical Chemistry (Universitat de Barcelona). With more than 40 scientific papers and book chapters to his name, he has been working for several years on the development of capillary electrophoresis, liquid chromatography, mass spectrometry, and high resolution mass spectrometry methods for the analysis of environmental and food samples. A field-amplified sample injection–capillary zone electrophoresis (FASI-CZE) method for the analysis of benzophenone (BP) UV filters in environmental water samples was developed, allowing the separation of all compounds in less than 8 min. A 9- to 25-fold sensitivity enhancement was obtained with FASI-CZE, achieving limits of detection down to 21–59 μg/L for most of the analyzed BPs, with acceptable run-to-run and day-to-day precisions (relative standard deviations lower than 17 %). In order to remove water sample salinity and to enhance FASI sensitivity, an off-line solid-phase extraction (SPE) procedure using a Strata X polymeric reversed-phase sorbent was used and afforded recoveries up to 72–90 % for most BPs. With the combination of off-line SPE and FASI-CZE, limits of detection in the range 0.06–0.6 μg/L in a river water matrix, representing a 2,400- to 6,500-fold enhancement, were obtained. Method performance was evaluated by quantifying a blank river water sample spiked at 1 μg/L. For a 95 % confidence level, no statistical differences were observed between found concentrations and spiked concentrations (probability at the confidence level, p value, of 0.60), showing that the proposed off-line SPE-FASI-CZE method is suitable for the analysis of BP UV filters in environmental water samples at low microgram per liter levels. The method was successfully applied to the analysis of BPs in river water samples collected up- and downstream of industrialized and urban areas, and in some drinking water samples.
Keywords: Solid-phase extraction; Field-amplified sample injection; Capillary zone electrophoresis; Benzophenone UV filters; Water analysis
Analysis of drug interactions with very low density lipoprotein by high-performance affinity chromatography by Matthew R. Sobansky; David S. Hage (6203-6211).
High-performance affinity chromatography (HPAC) was utilized to examine the binding of very low density lipoprotein (VLDL) with drugs, using R/S-propranolol as a model. These studies indicated that two mechanisms existed for the binding of R- and S-propranolol with VLDL. The first mechanism involved non-saturable partitioning of these drugs with VLDL, which probably occurred with the lipoprotein’s non-polar core. This partitioning was described by overall affinity constants of 1.2 (±0.3) × 106 M−1 for R-propranolol and 2.4 (±0.6) × 106 M−1 for S-propranolol at pH 7.4 and 37 °C. The second mechanism occurred through saturable binding by these drugs at fixed sites on VLDL, such as represented by apolipoproteins on the surface of the lipoprotein. The association equilibrium constants for this saturable binding at 37 °C were 7.0 (±2.3) × 104 M−1 for R-propranolol and 9.6 (±2.2) × 104 M−1 for S-propranolol. Comparable results were obtained at 20 and 27 °C for the propranolol enantiomers. This work provided fundamental information on the processes involved in the binding of R- and S-propranolol to VLDL, while also illustrating how HPAC can be used to evaluate relatively complex interactions between agents such as VLDL and drugs or other solutes.
Keywords: Very low density lipoprotein; Propranolol; Drug-protein binding; High-performance affinity chromatography; Frontal analysis
Quantification of cocaine and metabolites in exhaled breath by liquid chromatography-high-resolution mass spectrometry following controlled administration of intravenous cocaine by Kayla N. Ellefsen; Marta Concheiro; Olof Beck; David A. Gorelick; Sandrine Pirard; Marilyn A. Huestis (6213-6223).
Breath has been investigated as an alternative matrix for detecting recent cocaine intake; however, there are no controlled cocaine administration studies that investigated the drug’s disposition into breath. Breath was collected from 10 healthy adult cocaine users by asking them to breathe into a SensAbues device for 3 min before and up to 22 h following 25 mg intravenous (IV) cocaine dosing on days 1, 5, and 10, and assayed with a validated liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method to quantify breath cocaine, benzoylecgonine (BE), ecgonine methyl ester (EME), and norcocaine. The assay was linear from 25 to 1,000 pg/filter, extraction efficiencies were 83.6–126 %, intra- and inter-assay imprecision was <10.6 %, and bias was between −8.5 and 16.8 %. No endogenous or exogenous interferences were observed for more than 75 tested. Analytes were generally stable under short-term storage conditions. Ion suppression was less than 46 %. Of breath specimens collected after controlled cocaine administration, 2.6 % were positive for cocaine (26.1–66 pg/filter, 1–9.5 h), 0.72 % BE (83.3–151 pg/filter, 6.5–12.5 h), and 0.72 % EME (50–69.1 pg/filter, 6.5–12.5 h); norcocaine was not detected. Methanolic extraction of the devices themselves, after filters were removed, yielded 19.2 % positive cocaine tests (25.2–36.4 pg/device, 10 min–22 h) and 4.3 % positive BE tests (26.4–93.7 pg/device, 10 min–22 h), explaining differences between the two extraction techniques. These results suggest that the device reflects the drug in oral fluid as well as lung microparticles, while the filter reflects only drug-laden microparticles. A sensitive and specific method for cocaine, BE, EME, and norcocaine quantification in breath was developed and validated. Cocaine in breath identifies recent cocaine ingestion, but its absence does not preclude recent use. Graphical abstract ᅟ
Keywords: Cocaine; Exhaled breath; LC-HRMS; Metabolites; SensAbues
Surfactant protein C metabolism in human infants and adult patients by stable isotope tracer and mass spectrometry by Manuela Simonato; Aldo Baritussio; Barbara Pioselli; Carlo Ori; Silvia Catinella; Virgilio P. Carnielli; Paola E. Cogo (6225-6233).
Surfactant protein C (SP-C) is deemed as the surfactant protein most specifically expressed in type II alveolar epithelial cells and plays an important role in surfactant function. SP-C turnover in humans and its meaning in the clinical context have never been approached. In this study, we used mass spectrometry to investigate SP-C turnover in humans. We studied four infants and eight adults requiring mechanical ventilation. All patients had no lung disease. Patients received a 24-h continuous infusion of 13C-leucine as precursor of SP-C, and serial tracheal aspirates and plasma samples were obtained every 6 h till 48 h. SP-C was isolated from tracheal aspirates by sorbent-phase chromatography. 13C-leucine SP-C enrichment could be successfully measured in three infant and in four adult samples by using mass spectrometry coupled with a gas chromatographer. Median SP-C fractional synthesis rate, secretion time, and peak time were 15.7 (14.1–27.5) %/day, 6.0 (4.7–11.5) h, and 24 (20–27) h. In conclusion, this study shows that it is feasible to accurately determine SP-C turnover in humans by stable isotopes.
Keywords: Surfactant protein C; Lung surfactant; Isotope; Mass spectrometry
Solid-phase methylamidation for sialoglycomics by MALDI-MS by Henghui Li; Xing Zhao; Qiwei Zhang; Xiaojun Feng; Bi-Feng Liu; Xin Liu (6235-6246).
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been a major approach for glycan analysis. However, the preferential cleavage of the sialic acid moiety by in- and post-source decay influences the determination of sialylated glycans by MALDI-MS. Many chemical derivatization methods were introduced to stabilize the sialylated glycan during MALDI-MS. Among current derivatization methods, methylamidation is a promising means for simultaneous analysis of natural sialylated glycans regardless of their sialic acid linkage types. Here, a novel derivatization method was developed, in which proteins were conjugated on the solid-phase support in order to stabilize the sialic acids by methylamidation and to reduce sample loss and contamination during the derivatization process. This derivatization strategy was used to investigate N-glycans from fetuin, a glycoprotein containing different types of complex N-glycans. The developed method was also applied to the N-glycan profiling of human serum from patients and healthy volunteers. Results were consistent with N-glycan profiling by HPLC-fluorescence detection. This new method provided a sensitive, simple, and robust approach for profiling glycan structures of complex samples.
Keywords: Solid-phase labeling; Glycosylation; Matrix-assisted laser desorption/ionization mass spectrometry; Methylamidation; Sialic acid; High-performance liquid chromatography
Quantitative proteomics reveals the kinetics of trypsin-catalyzed protein digestion by Yanbo Pan; Kai Cheng; Jiawei Mao; Fangjie Liu; Jing Liu; Mingliang Ye; Hanfa Zou (6247-6256).
Trypsin is the popular protease to digest proteins into peptides in shotgun proteomics, but few studies have attempted to systematically investigate the kinetics of trypsin-catalyzed protein digestion in proteome samples. In this study, we applied quantitative proteomics via triplex stable isotope dimethyl labeling to investigate the kinetics of trypsin-catalyzed cleavage. It was found that trypsin cleaves the C-terminal to lysine (K) and arginine (R) residues with higher rates for R. And the cleavage sites surrounded by neutral residues could be quickly cut, while those with neighboring charged residues (D/E/K/R) or proline residue (P) could be slowly cut. In a proteome sample, a huge number of proteins with different physical chemical properties coexists. If any type of protein could be preferably digested, then limited digestion could be applied to reduce the sample complexity. However, we found that protein abundance and other physicochemical properties, such as molecular weight (Mw), grand average of hydropathicity (GRAVY), aliphatic index, and isoelectric point (pI) have no notable correlation with digestion priority of proteins. Graphical Abstract Sequence logos of four cleavage site types with different kinetics (very fast, fast, slow, and very slow sites)
Keywords: Trypsin; Protein digestion; Kinetics; Stable isotope dimethyl labeling; Mass spectrometry
Separation and quantification of monoclonal-antibody aggregates by hollow-fiber-flow field-flow fractionation by Jun Fukuda; Takafumi Iwura; Shigehiro Yanagihara; Kenji Kano (6257-6264).
Hollow-fiber-flow field-flow fractionation (HF5) separates protein molecules on the basis of the difference in the diffusion coefficient, and can evaluate the aggregation ratio of proteins. However, HF5 is still a minor technique because information on the separation conditions is limited. We examined in detail the effect of different settings, including the main-flow rate, the cross-flow rate, the focus point, the injection amount, and the ionic strength of the mobile phase, on fractographic characteristics. On the basis of the results, we proposed optimized conditions of the HF5 method for quantification of monoclonal antibody in sample solutions. The HF5 method was qualified regarding the precision, accuracy, linearity of the main peak, and quantitation limit. In addition, the HF5 method was applied to non-heated Mab A and heat-induced-antibody-aggregate-containing samples to evaluate the aggregation ratio and the distribution extent. The separation performance was comparable with or better than that of conventional methods including analytical ultracentrifugation–sedimentation velocity and asymmetric-flow field-flow fractionation.
Keywords: Antibodies aggregates; Hollow-fiber-flow field-flow fractionation; Size-exclusion chromatography; Analytical ultracentrifugation; Asymmetric-flow field-flow fractionation
Site-specific qualitative and quantitative analysis of the N- and O-glycoforms in recombinant human erythropoietin by Jing Jiang; Fang Tian; Yun Cai; Xiaohong Qian; Catherine E. Costello; Wantao Ying (6265-6274).
Recombinant human erythropoietin (rhEPO) has been extensively used as a pharmaceutical product for treating anemia. Glycosylation of rhEPO affects the biological activity, immunogenicity, pharmacokinetics, and in-vivo clearance rate of rhEPO. Characterization of the glycosylation status of rhEPO is of great importance for quality control. In this study, we established a fast and comprehensive approach for reliable characterization and relative quantitation of rhEPO glycosylation, which combines multiple-enzyme digestion, hydrophilic-interaction chromatography (HILIC) enrichment of glycopeptides, and tandem mass spectrometry (MS) analysis. The N-linked and O-linked intact glycopeptides were analyzed with high-resolution and high-accuracy (HR–AM) mass spectrometry using an Orbitrap. In total, 74 intact glycopeptides from four glycosylation sites at N24, N38, N83, and O126 were identified, with the simultaneous determination of peptide sequences and glycoform compositions. The extracted ion chromatograms based on the HR–AM data enabled relative quantification of glycoforms. Our results could be extended to quality control of rhEPO or could help establish detection approaches for glycosylation of other proteins. Graphical Abstract ᅟ
Keywords: Site-specific glycosylation; Recombinant human erythropoietin; Tandem mass spectrometry
Evaluation of molecularly imprinted polymers using 2′,3′,5′-tri-O-acyluridines as templates for pyrimidine nucleoside recognition by Aleksandra Krstulja; Stefania Lettieri; Andrew J. Hall; Raphael Delépée; Patrick Favetta; Luigi A. Agrofoglio (6275-6284).
In this paper, we describe the synthesis and evaluation of molecularly imprinted polymers (MIPs), prepared using 2′,3′,5′-tri-O-acyluridines as ‘dummy’ templates, for the selective recognition of uridine nucleosides. The MIPs were synthesised using a non-covalent approach with 2,6-bis-acrylamidopyridine (BAAPy) acting as the binding monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linking agent. The MIPs were evaluated in terms of capacity, selectivity and specificity by analytical and frontal liquid chromatography measurements. The results obtained in organic mobile phases suggest that the nucleosides are specifically bound to the polymer by the complementary hydrogen bonding motifs of the binding monomer and the nucleoside bases. The MIPs exhibited relatively high imprinting factors for 2′,3′,5′-tri-O-acyluridines, while they did not show any binding capacity for other nucleosides lacking the imide moiety on their base. Moreover, the presence of ester-COO groups in the EGDMA cross-linker may lead to the formation of additional hydrogen bonds with the 2′,3′ and/or 5′-OH of sugar part, allowing enhancement of the recognition of the uridine nucleosides. In aqueous media, results show that the binding is driven by hydrophobic interactions.
Keywords: Hydrogen bonds; Molecular recognition; 2′,3′,5′-Tri-O-acyluridines; Nucleosides; Imprinting
CIEF separation, UV detection, and quantification of ampholytic antibiotics and bacteria from different matrices by Marie Horká; Marie Vykydalová; Filip Růžička; Jiří Šalplachta; Veronika Holá; Milada Dvořáčková; Anna Kubesová; Karel Šlais (6285-6296).
The effect of antibiotics on the microbial cells and concentration of antibiotics in the human body is essential for the effective use of antimicrobial therapy. The capillary isoelectric focusing is a suitable technique for the separation and the detection of bacteria, and amphoteric substances from nature. However, the determination of isoelectric points of ampholytic antibiotics by conventional techniques is time consuming. For this reason, capillary isoelectric focusing seems to be appropriate as a simple and reliable way for establishing them. The separation conditions for the capillary isoelectric focusing of selected ampholytic antibiotics with known isoelectric points and pK as, ampicillin (pI 4.9), ciprofloxacin (pI 7.4), ofloxacin (pI 7.1), tetracycline (pI 5.4), tigecycline (pI 9.7), and vancomycin (pI 8.1), were found and optimized in the suitable pH ranges pH 2.0–5.3, 2.0–9.6, and 9.0–10.4. The established values of isoelectric points correspond with those found in the literature except tigecycline. Its pI was not found in the literature. As an example of a possible procedure for direct detection of both ampholytic antibiotics and bacteria, Staphylococcus epidermidis, in the presence of culture media or whole human blood, was found. The changes of the bacterial cells after their treatment with tetracycline were confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Capillary isoelectric focusing allows the fast and simple determination of isoelectric points of relevant antibiotics, their quantification from the environment, as well as studying their effectiveness on microorganisms in biological samples. Graphical Abstract ᅟ
Keywords: Capillary isoelectric focusing with UV detection; Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; Ampholytic antibiotics; Staphylococcus epidermidis ; Human whole blood
Potential of liquid-isoelectric-focusing protein fractionation to improve phosphoprotein characterization of Pseudomonas aeruginosa PA14 by Tassadit Ouidir; Frédérique Jarnier; Pascal Cosette; Thierry Jouenne; Julie Hardouin (6297-6309).
Protein phosphorylation on serine, threonine, and tyrosine is known to be involved in a wide variety of cellular processes and signal transduction in bacteria. Bacterial-proteome analysis is required to determine which proteins have been conditionally expressed and whether any post-translational modifications are present. One of the greatest challenges of proteome analysis is the fractionation of these complex protein mixtures to detect low-abundance phosphoproteins. Liquid-phase isoelectric focusing (IEF) is a promising analytical tool in proteomics, but as far as we are aware no work has studied the reproducibility of this approach. In this study, we investigated the phosphoproteome of Pseudomonas aeruginosa strain PA14. We first tested in-solution IEF protein fractionation, and then used this technique to fractionate the proteins in the complex mixture. Next, phosphopeptides were enriched with titanium dioxide and analyzed by high-resolution, high-accuracy liquid chromatography–mass spectrometry. With this approach, we succeeded in characterizing 73 unique phosphorylated peptides belonging to 63 proteins. Interestingly, we observed a higher percentage of modified tyrosine, revealing the importance of this phosphorylated residue in bacteria.
Keywords: Protein fractionation; Phosphoproteins; Proteomics; Mass spectrometry
Characterization of poly(2-vinylpyridine)-block-poly(methyl methacrylate) copolymers and blends of their homopolymers by liquid chromatography at critical conditions by Muhammad Imran Malik; Tooba Mahboob; Shakil Ahmed (6311-6317).
Poly(2-vinylpyridine)s (P2VPs) are important polymers with extensive applications in modern day material science. P2VP is an exceptional case for liquid chromatography because of certain polar interactions with most of the stationary phases. In the present study, we established the critical adsorption point (CAP) of P2VP for the first time. The effectiveness of the method is demonstrated by analyses of blends and block copolymers of P2VP and PMMA. The CAP of PMMA is established for determination of molar mass of P2VP component of above mentioned blends and block copolymers. The methods successfully demonstrate the separation of both types of homopolymers from the rest of the samples in conjunction with the determination of molar mass distribution of noncritical block or component. Graphical Abstract ᅟ
Keywords: Polymer blends; Hybrid materials; Block copolymers; Critical adsorption Point (CAP); Liquid chromatography at critical conditions (LCCC); Poly(2-vinylpyridine)
Identification of 3-chloro-1,2-propandiol using molecularly imprinted composite solid-phase extraction materials by Yun Li; Chuangmu Zheng; Xiulan Sun; Ben Ouyang; Ping Ni; Yingzhi Zhang (6319-6327).
A novel molecularly imprinted material based on silica microparticles was synthesized by surface polymerization with 3-chloro-1,2-propandiol (3-MCPD) as a template molecule. The molecularly imprinted polymer (MIP) was characterized by infrared spectroscopy and scanning electron microscopy. The adsorption of 3-MCPD by MIP was measured by gas chromatography with electron capture detection (GC-ECD) and an equilibrium binding experiment. Scatchard analysis revealed that the maximum apparent binding capacities of the MIP and non-imprinted polymer (NIP) were 67.64 and 23.31 μmol/g, respectively. The new adsorbent was successfully used in solid-phase extraction (SPE) to selectively enrich and determine 3-MCPD in soy sauce samples. The MIP-SPE column achieves recoveries higher than 92.7 % with a relative standard deviation of less than 1.83 %. The MIP-SPE-GC protocol improved the selectivity and eliminated the effects of template leakage on quantitative analysis and could be used for the determination of 3-MCPD in other complex food samples. Graphical Abstract The MIP-SPE column developed by us achieves recoveries higher than 92.7 % with a relative standard deviation of less than 1.83 % for determining the 3-MCPD in the soy sauce matrix (mixed with 3-MCPD, 2-MPCD and 1,3-DCP).
Keywords: 3-MCPD; Molecular imprinting; Silica; Microparticles; Adsorption
UV-polymerized butyl methacrylate monoliths with embedded carboxylic single-walled carbon nanotubes for CEC applications by María Navarro-Pascual-Ahuir; Rafael Lucena; Soledad Cárdenas; Guillermo Ramis-Ramos; Miguel Valcárcel; José Manuel Herrero-Martínez (6329-6336).
The preparation of polymeric monoliths with embedded carboxy-modified single-walled carbon nanotubes (c-SWNTs) and their use for capillary electrochromatography (CEC) is described. Carbon nanotube composites were obtained by preparing a polymerization mixture in the presence of increasing c-SWNT concentrations, followed by UV initiation. The novel stationary phases were studied by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Using short UV-polymerization times, the optimized porogenic solvent (a binary mixture of 1,4-butanediol and 2-propanol) gave rise to polymeric beds with homogenously dispersed embedded c-SWNTs. The CEC features of these monoliths were evaluated using polycyclic aromatic hydrocarbons (PAHs), non-steroidal anti-inflammatory drugs (NSAIDs) and chiral compounds. The monolith prepared in the presence of c-SWNTs showed enhanced resolution of the text mixtures, including a remarkable capability to separate enantiomers. Graphical Abstract UV-polymerized polymeric monoliths with embedded c-SWNTs for CEC applications
Keywords: Carboxylic carbon nanotubes; Methacrylate monolithic columns; UV initiation; CEC; Chiral separations
A wide range optical pH sensor for living cells using Au@Ag nanoparticles functionalized carbon nanotubes based on SERS signals by Peng Chen; Zhuyuan Wang; Shenfei Zong; Hui Chen; Dan Zhu; Yuan Zhong; Yiping Cui (6337-6346).
p-Aminothiophenol (pATP) functionalized multi-walled carbon nanotubes (MWCNTs) have been demonstrated as an efficient pH sensor for living cells. The proposed sensor employs gold/silver core-shell nanoparticles (Au@Ag NPs) functionalized MWCNTs hybrid structure as the surface-enhanced Raman scattering (SERS) substrate and pATP molecules as the SERS reporters, which possess a pH-dependent SERS performance. By using MWCNTs as the substrate to be in a state of aggregation, the pH sensing range could be extended to pH 3.0∼14.0, which is much wider than that using unaggregated Au@Ag NPs without MWCNTs. Furthermore, the pH-sensitive performance was well retained in living cells with a low cytotoxicity. The developed SERS-active MWCNTs-based nanocomposite is expected to be an efficient intracellular pH sensor for bio-applications.
Keywords: p-Aminothiophenol; SERS; Multi-wall carbon nanotubes; pH sensor
Applicability of UV laser-induced solid-state fluorescence spectroscopy for characterization of solid dosage forms by Eva Woltmann; Hans Meyer; Diana Weigel; Heinz Pritzke; Tjorben N. Posch; Pablo A. Kler; Klaus Schürmann; Jörg Roscher; Carolin Huhn (6347-6362).
High production output of solid pharmaceutical formulations requires fast methods to ensure their quality. Likewise, fast analytical procedures are required in forensic sciences, for example at customs, to substantiate an initial suspicion. We here present the design and the optimization of an instrumental setup for rapid and non-invasive characterization of tablets by laser-induced fluorescence spectroscopy (with a UV-laser (λ ex = 266 nm) as excitation source) in reflection geometry. The setup was first validated with regard to repeatability, bleaching phenomena, and sensitivity. The effect on the spectra by the physical and chemical properties of the samples, e.g. their hardness, homogeneity, chemical composition, and granule grain size of the uncompressed material, using a series of tablets, manufactured in accordance with design of experiments, was investigated. Investigation of tablets with regard to homogeneity, especially, is extremely important in pharmaceutical production processes. We demonstrate that multiplicative scatter correction is an appropriate tool for data preprocessing of fluorescence spectra. Tablets with different physical and chemical characteristics can be discriminated well from their fluorescence spectra by subjecting the results to principal component analysis.
Keywords: Tablet analysis; Solid-state fluorescence spectroscopy; Grain size; Photobleaching; Scattering effects; Homogeneity
Electrochemical magnetoimmunosensor for the ultrasensitive determination of interleukin-6 in saliva and urine using poly-HRP streptavidin conjugates as labels for signal amplification by I. Ojeda; M. Moreno-Guzmán; A. González-Cortés; P. Yáñez-Sedeño; J. M. Pingarrón (6363-6371).
A novel magnetoimmunosensor design for interleukin-6 (IL-6) which involved the covalent immobilization of anti-IL-6 antibodies onto carboxyl-functionalized magnetic microparticles and a sandwich-type immunoassay with signal amplification using poly-HRP-streptavidin conjugates is reported. All the variables concerning the preparation and the electroanalytical performance of the immunosensor were optimized. The use of poly-HRP-strept conjugates as enzymatic labels instead of conventional HRP-strept allowed enhanced signal-to-blank current ratios to be obtained. A linear calibration plot between the measured steady-state current and the log of IL-6 concentration was achieved in the 1.75 to 500 pg/mL range, which was not feasible when using HRP-strep as label. A limit of detection of 0.39 pg/mL IL-6 was obtained. The anti-IL-6-MB conjugates exhibited an excellent storage stability providing amperometric responses with no significant loss during at least 36 days. The magnetoimmunosensor showed also an excellent selectivity against potentially interfering substances. The immunosensor was used to determine IL-6 in urine samples spiked at three different concentration levels with clinical relevance. Moreover, IL-6 was measured in three different saliva samples corresponding to a periodontitis patient, a smoker volunteer, and a non-smoker volunteer. The obtained results were statistically in agreement with those provided by a commercial ELISA kit.
Keywords: Interleukin-6; Electrochemical magnetoimmunosensor; Signal amplification; Poly-HRP-streptavidin; Urine; Saliva
Analysis of N-acylhomoserine lactone dynamics in continuous cultures of Pseudomonas putida IsoF by use of ELISA and UHPLC/qTOF-MS-derived measurements and mathematical models by Katharina Buddrus-Schiemann; Martin Rieger; Marlene Mühlbauer; Maria Vittoria Barbarossa; Christina Kuttler; Burkhard A. Hense; Michael Rothballer; Jenny Uhl; Juliano R. Fonseca; Philippe Schmitt-Kopplin; Michael Schmid; Anton Hartmann (6373-6383).
In this interdisciplinary approach, the dynamics of production and degradation of the quorum sensing signal 3-oxo-decanoylhomoserine lactone were studied for continuous cultures of Pseudomonas putida IsoF. The signal concentrations were quantified over time by use of monoclonal antibodies and ELISA. The results were verified by use of ultra-high-performance liquid chromatography. By use of a mathematical model we derived quantitative values for non-induced and induced signal production rate per cell. It is worthy of note that we found rather constant values for different rates of dilution in the chemostat, and the values seemed close to those reported for batch cultures. Thus, the quorum-sensing system in P. putida IsoF is remarkably stable under different environmental conditions. In all chemostat experiments, the signal concentration decreased strongly after a peak, because emerging lactonase activity led to a lower concentration under steady-state conditions. This lactonase activity probably is quorum sensing-regulated. The potential ecological implication of such unique regulation is discussed.
Keywords: Pseudomonas putida IsoF; Continuous culture; N-acylhomoserine lactones; Mathematical modelling; ELISA; Quorum sensing
Correction of the lack of commutability between plasmid DNA and genomic DNA for quantification of genetically modified organisms using pBSTopas as a model by Li Zhang; Yuhua Wu; Gang Wu; Yinglong Cao; Changming Lu (6385-6397).
Plasmid calibrators are increasingly applied for polymerase chain reaction (PCR) analysis of genetically modified organisms (GMOs). To evaluate the commutability between plasmid DNA (pDNA) and genomic DNA (gDNA) as calibrators, a plasmid molecule, pBSTopas, was constructed, harboring a Topas 19/2 event-specific sequence and a partial sequence of the rapeseed reference gene CruA. Assays of the pDNA showed similar limits of detection (five copies for Topas 19/2 and CruA) and quantification (40 copies for Topas 19/2 and 20 for CruA) as those for the gDNA. Comparisons of plasmid and genomic standard curves indicated that the slopes, intercepts, and PCR efficiency for pBSTopas were significantly different from CRM Topas 19/2 gDNA for quantitative analysis of GMOs. Three correction methods were used to calibrate the quantitative analysis of control samples using pDNA as calibrators: model a, or coefficient value a (Cva); model b, or coefficient value b (Cvb); and the novel model c or coefficient formula (Cf). Cva and Cvb gave similar estimated values for the control samples, and the quantitative bias of the low concentration sample exceeded the acceptable range within ±25 % in two of the four repeats. Using Cfs to normalize the Ct values of test samples, the estimated values were very close to the reference values (bias −13.27 to 13.05 %). In the validation of control samples, model c was more appropriate than Cva or Cvb. The application of Cf allowed pBSTopas to substitute for Topas 19/2 gDNA as a calibrator to accurately quantify the GMO. Graphical Abstract ᅟ
Keywords: GMO quantification; Plasmid DNA calibrator; Genomic DNA calibrator; Commutability; Coefficient value; Coefficient formula
Fatty acid desaturation index in human plasma: comparison of different analytical methodologies for the evaluation of diet effects by Jost Klawitter; Stephan Bek; Marjorie Zakaria; Chenhui Zeng; Andrea Hornberger; Richard Gilbert; Touraj Shokati; Jelena Klawitter; Uwe Christians; K. Olaf Boernsen (6399-6408).
Stearoyl-CoA desaturase 1 (SCD1) plays a role in the development of obesity and related conditions, such as insulin resistance, and potentially also in neurological and heart diseases. The activity of SCD1 can be monitored using the desaturation index (DI), the ratio of product (16:1n-7 and 18:1n-9) to precursor (16:0 and 18:0) fatty acids. Here, different analytical strategies were applied to identify the method which best supports SCD1 biology. A novel effective approach was the use of the SCD1-independent fatty acid (16:1n-10) as a negative control. The first approach was based on a simple extraction followed by neutral loss triglyceride fatty acid analysis. The second approach was based on the saponification of triglycerides followed by fatty acid analysis (specific for the position of the double bond within monounsaturated fatty acids (MUFAs)). In addition to the analytical LC-MS assays, different matrices (plasma total triglyceride fraction and the very low-density lipoprotein (VLDL) fraction) were investigated to identify the best for studying changes in SCD1 activity. Samples from volunteers on a high-carbohydrate diet were analyzed. Both ultra HPLC (UHPLC)-MS-based assays showed acceptable accuracies (75–125 % of nominal) and precisions (<20 %) for the analysis of DI-specific fatty acids in VLDL and plasma. The most specific assay for the analysis of the liver SCD activity was then validated for specificity and selectivity, intra- and interday accuracy and precision, matrix effects, dilution effects, and analyte stability. After 3 days of high-carbohydrate diet, only the specific fatty acids in human plasma VLDL showed a significant increase in DI and associated SCD1 activity.
Keywords: Bioanalytical methods; Biological samples; Enzymes; UHPLC; Mass spectrometry
A novel and rapid HPGPC-based strategy for quality control of saccharide-dominant herbal materials: Dendrobium officinale, a case study by Jun Xu; Song-Lin Li; Rui-Qi Yue; Chun-Hay Ko; Jiang-Miao Hu; Jing Liu; Hing-Man Ho; Tao Yi; Zhong-Zhen Zhao; Jun Zhou; Ping-Chung Leung; Hu-Biao Chen; Quan-Bin Han (6409-6417).
Qualitative and quantitative characterization of natural saccharides, especially polysaccharides, in herb materials remains a challenge due to their complicated structures and high macromolecular masses. Currently available methods involve time-consuming and complicated operations, and present poor specificity. Here, a novel and rapid high-performance gel permeation chromatography (HPGPC)-based approach is described for quality assessment of saccharide-dominant herbal materials by simultaneous qualitative and quantitative analysis of saccharide components. Dendrobium officinale, one of the rarest tonic herbs worldwide, was employed as the model herb in this study. First, a HPGPC fingerprint based on the molecular weight distribution of its carbohydrate components was established for qualitative identification of D. officinale. Then, HPGPC-guided dominant holistic polysaccharide marker was separated using ultra-filtration followed by HPGPC determination for quantitative evaluation of D. officinale. The experimental results suggest that this method is more efficient, stable, and convenient compared with the currently available methods for authentication and quality evaluation of D. officinale, and we expect the method will have similar advantages when used for quality control of other saccharide-dominant herbal materials and products. Graphical Abstract The characteristic HPGPC fingerprint of Dendrobium officinale compared with other confused Dendrobium species
Keywords: HPGPC fingerprints; Saccharide-dominant herbal materials; Holistic polysaccharide marker; Quality evaluation; Dendrobium officinale
Online solid phase extraction LC–MS/MS method for the analysis of succinate dehydrogenase inhibitor fungicides and its applicability to surface water samples by Anna Gulkowska; Ignaz J. Buerge; Thomas Poiger (6419-6427).
A sensitive and selective analytical method, based on online solid phase extraction coupled to LC–MS/MS, was developed and validated to determine traces of several recently introduced fungicides in surface water and wastewater. The list of target analytes included eight succinate dehydrogenase inhibitors (bixafen, boscalid, fluopyram, flutolanil, fluxapyroxad, isopyrazam, penflufen, and penthiopyrad), and two other fungicides with different modes of action, fenpyrazamine and fluopicolide. Detection and quantification limits in various matrices were in the range of 0.1 to 2 and 0.5 to 10 ng/L, respectively. Moderate signal suppression was observed in surface water (≤15 %) and wastewater (≤25 %) and was well compensated by the selected internal standard. The intra- and inter-day precisions were generally <10 and <20 %, respectively. The applicability of the method was demonstrated in a study on the occurrence of fungicides in the river Glatt, Switzerland, that drains a catchment area of 419 km2 with a substantial proportion of agricultural land. Of the studied compounds, only boscalid and fluopicolide were detected in flow-proportional weekly composite samples, generally at low concentrations up to 15 and 5 ng/L, respectively. While fluopicolide was detected in only 30 % of the samples above the LOD of 0.5 ng/L, boscalid was detected in all samples analyzed between March and October 2012. Graphical Abstract Concentration of the fungicides boscalid and fluopicolide in flow-proportional weekly-composite watersamples from River Glatt, Switzerland in 2012
Keywords: Succinate dehydrogenase inhibitors; Fungicides; Carboxamides; LC–MS/MS; Online SPE; Boscalid
Characterization and analysis of structural isomers of dimethyl methoxypyrazines in cork stoppers and ladybugs (Harmonia axyridis and Coccinella septempunctata) by Petra Slabizki; Charlotte Legrum; Reinhard Meusinger; Hans-Georg Schmarr (6429-6439).
The three constitutional isomers of dimethyl-substituted methoxypyrazines: 3,5-dimethyl-2-methoxypyrazine 1; 2,5-dimethyl-3-methoxypyrazine 2; and 2,3-dimethyl-5-methoxypyrazine 3 are potent flavor compounds with similar mass spectrometric, gas chromatographic, and nuclear magnetic resonance spectroscopic behavior. Therefore, unambiguous analytical determination is critical, particularly in complex matrices. The unequivocal identification of 1–3 could be achieved by homo- and heteronuclear NMR correlation experiments. The observed mass fragmentation for 1–3 is proposed and discussed, benefitting from synthesized partially deuterated 1 and 2. On common polar and apolar stationary phases used in gas chromatography (GC) 1 and 2 show similar behavior whereas 3 can be separated. In our focus on off-flavor analysis with respect to wine aroma, 1 has been described as a “moldy” off-flavor compound in cork and 2 as a constituent in Harmonia axyridis contributing to the so-called “ladybug taint,” whereas 3 has not yet been described as a constituent of wine aroma. A successful separation of 1 and 2 could be achieved on octakis-(2,3-di-O-pentyl-6-O-methyl)-γ-cyclodextrin as stationary phase in GC. Applying heart-cut multidimensional GC analysis with tandem mass spectrometric detection we could confirm the presence of 1 as a “moldy” off-flavor compound in cork. However, in the case of Harmonia axyridis, a previous identification of 2 has to be reconsidered. In our experiments we identified the constitutional isomer 1, which was also found in Coccinella septempunctata, another species discussed with respect to the “ladybug taint.” The analysis of such structurally related compounds is a demonstrative example for the importance of a chromatographic separation, as mass spectrometric data by itself could not guarantee the unequivocal identification.
Keywords: Dimethyl methoxypyrazines; NMR; H/C MDGC-MS-MS; Linear retention index; Ladybug; Cork
A novel approach using electrospray ionization mass spectrometry to study competitive binding of small molecules with mixed DNA sequences by Sarah Laughlin; Siming Wang; Arvind Kumar; David W. Boykin; W. David Wilson (6441-6445).
Minor groove binding compounds have been shown to induce changes in global DNA conformation, allosterically inhibiting DNA-protein interactions necessary for transcriptional processes. Many minor groove binders are specific for AT base pairs but have little preference over alternating AT or A-tract sequences. Few compounds, other than polyamides, show selectivity for mixed sequences with AT and GC base pairs. Electrospray ionization mass spectrometry (ESI-MS) can provide insight on the stoichiometry and relative affinities in minor groove recognition of different DNA sequences with a library of minor groove binders. A goal in our current research is to develop new compounds that recognize mixed sequences of DNA. In an effort to optimize screening for compounds that target mixed AT and GC base pair sequences of DNA, ESI-MS was used to study the competitive binding of compounds with a mixed set of DNA sequences. The method identified preferred binding sites, relative affinities, and concentration-dependent binding stoichiometry for the minor groove binding compounds netropsin and DB75 with AT-rich sequences and DB293 with ATGA and AT sites. Graphical abstract A cartoon representation for screening complex interactions by ESI-MS with multiple, mixed DNA sequences in a single solution. An oversimplification shows several distinguishable species and spectra of free DNA and DNA-ligand complexes
Keywords: Electrospray ionization mass spectrometry; Mixed DNA sequences; Selectivity; Minor groove recognition; Minor groove binders
xMAP-based analysis of three most prevalent staphylococcal toxins in Staphylococcus aureus cultures by Maria A. Simonova; Elena. E. Petrova; Olga A. Dmitrenko; Ravilya L. Komaleva; Natalia S. Shoshina; Larisa V. Samokhvalova; Tatiana I. Valyakina; Eugene V. Grishin (6447-6452).
Detection of staphylococcal toxins presents a great interest for medical diagnostics. Screening of clinical samples for the presence of several types of staphylococcal toxins using traditional methods—biological tests on animals or cell cultures as well as ELISA—is laborious. Multiplex detection methods would simplify testing. We have designed an xMAP-based assay to detect three staphylococcal toxins—enterotoxins A and B (SEA and SEB) and toxic shock syndrome toxin (TSST)—in cultural supernatants obtained from different strains of Staphylococcus aureus. The limits of detection of SEA, SEB, and TSST multiplex detection in S. aureus growth medium were 10, 1,000, and 5 pg/mL, respectively. Fifty-nine samples of S. aureus cultural supernatants were tested with the xMAP assay. The developed assay has proved highly effective detection of the natural toxins in the samples obtained due to bacterial cells cultivation. In prospect, the developed test system can be used in clinical diagnostics and in monitoring of foodstuffs and environmental objects.
Keywords: Monoclonal antibodies; Staphylococcal toxins; xMAP immunoassay; Multiplex assay