Analytical and Bioanalytical Chemistry (v.396, #4)
James Weifu Lee, Robert S. Foote (Eds.): Micro and nano technologies in bioanalysis. Methods and protocols by Rosario Pereiro (1371-1372).
Quartz crystal microbalance, a valuable tool for elucidation of interactions between apoB-100 peptides and extracellular matrix components by Lucia D’Ulivo; Julien Saint-Guirons; Björn Ingemarsson; Marja-Liisa Riekkola (1373-1380).
Atherosclerosis has received wide attention as a primary cause of premature death in developed countries. The retention of low-density lipoprotein (LDL) particles in the intima, the inner layer of the capillaries, has been imputed as the main cause of the development of atherosclerotic plaques. The entrapment of LDL is mainly due to the specific interaction between the lysine-rich site on apolipoprotein B-100 (apoB-100), a major apolipoprotein of LDL, and extracellular matrix (ECM) components such as collagen, proteoglycans, and glycosaminoglycans (GAGs). Although valuable techniques already exist for studies on apoB-100 and ECM interactions, there is continued need for miniaturized tools that can complement the tools already available and even provide totally new data. This work explores the applicability of the quartz crystal microbalance (QCM) for interaction studies between apoB-100 peptide fragments and various components of the ECM. Two positive peptide fragments, PP and PP2, and two components of the ECM, collagen I and a selected GAG, chondroitin 6-sulfate (C6S), were immobilized on polystyrene and carboxyl sensor chips. C6S was injected as analyte for PP- and PP2-coated surfaces, while PP was the analyte for collagen I and C6S surfaces. The estimated dissociation constant (K D) indicates that the interactions occur via the positive residues, lysine and arginine, of apoB-100. The continuous-flow QCM system employed in this study is shown to be an excellent tool for the elucidation of interactions between these types of biomolecules. Figure Binding of PP to a C6S aldehyde coupled carboxyl crystal. PP concentrations ranged from 50 to 250 µg/mL. Running buffer: PBS pH 7.4. Flow rate: 25 µL/min. Experiments were carried out at room temperature
Keywords: Apolipoprotein B-100; Atherosclerosis; Collagen I; Extracellular matrix; Low-density lipoproteins; Quartz crystal microbalance
SERS as tool for the analysis of DNA-chips in a microfluidic platform by Katharina K. Strelau; Robert Kretschmer; Robert Möller; Wolfgang Fritzsche; Jürgen Popp (1381-1384).
A sequence-specific detection method of DNA is presented combining a solid chip surface for immobilisation of capture DNAs with a microfluidic platform and a readout of the chip based on SERS. The solid chip surface is used for immobilisation of different capture DNAs, where target strands can be hybridised and unbound surfactants can be washed away. For the detection via SERS, short-labelled oligonucleotides are hybridised to the target strands. This technique is combined with a microfluidic platform that enables a fast and automated preparation process. By applying a chip format, the problems of sequence-specific DNA detection in solution phase by means of SERS can be overcome. With this setup, we are able to distinguish between different complementary and non-complementary target sequences in one sample solution.
Keywords: SERS; DNA detection; Microfluidics; Multiplexing; Biochip
Metabolomic investigation of gastric cancer tissue using gas chromatography/mass spectrometry by Hao Wu; Ruyi Xue; Zhaoqing Tang; Chunhui Deng; Taotao Liu; Huazong Zeng; Yihong Sun; Xizhong Shen (1385-1395).
Gastric cancer screening or diagnosis is mainly based on endoscopy and biopsy. The aim of this study was to identify the difference of metabolomic profile between normal and malignant gastric tissue, and to further explore tumor biomarkers. Chemical derivatization together with gas chromatography/mass spectrometry (GC/MS) was utilized to obtain the metabolomic information of the malignant and non-malignant tissues of gastric mucosae in 18 gastric cancer patients. Acquired metabolomic data was analyzed using the Wilcoxon rank sum test to find the tissue metabolic biomarkers for gastric cancer. A diagnostic model for gastric cancer was constructed using principal component analysis (PCA), and was assessed with receiver-operating characteristic (ROC) curves. Results showed that 18 metabolites were detected differently between the malignant tissues and the adjacent non-malignant tissues of gastric mucosa. Five metabolites were also detected differently between the non-invasive tumors and the invasive tumors. The diagnostic model could discriminate tumors from normal mucosae with an area under the curve (AUC) value of 0.9629, and another diagnostic model constructed for clinical staging was assessed with an AUC value of 0.969. We conclude that the metabolomic profile of malignant gastric tissue was different from normal, and that the selected tissue metabolites could probably be applied for clinical diagnosis or staging for gastric cancer.
Keywords: Metabolomic profile; Gastric cancer; Biomarker; Gas chromatography/mass spectrometry
A rapid and universal bacteria-counting approach using CdSe/ZnS/SiO2 composite nanoparticles as fluorescence probe by Xin Fu; Kelong Huang; Suqin Liu (1397-1404).
In this paper, a rapid, simple, and sensitive method was described for detection of the total bacterial count using SiO2-coated CdSe/ZnS quantum dots (QDs) as a fluorescence marker that covalently coupled with bacteria using glutaraldehyde as the crosslinker. Highly luminescent CdSe/ZnS were prepared by applying cadmium oxide and zinc stearate as precursors instead of pyrophoric organometallic precursors. A reverse-microemulsion technique was used to synthesize CdSe/ZnS/SiO2 composite nanoparticles with a SiO2 surface coating. Our results showed that CdSe/ZnS/SiO2 composite nanoparticles prepared with this method possessed highly luminescent, biologically functional, and monodispersive characteristics, and could successfully be covalently conjugated with the bacteria. As a demonstration, it was found that the method had higher sensitivity and could count bacteria in 3 × 102 CFU/mL, lower than the conventional plate counting and organic dye-based method. A linear relationship of the fluorescence peak intensity (Y) and the total bacterial count (X) was established in the range of 3 × 102–107 CFU/mL using the equation Y = 374.82X − 938.27 (R = 0.99574). The results of the determination for the total count of bacteria in seven real samples were identical with the conventional plate count method, and the standard deviation was satisfactory. Figure The synthesis and coupling process of CdSe/ZnS/SiO2 composite nanoparticles with bacterial cells.
Keywords: CdSe/ZnS/SiO2 nanoparticles; Bacterial count; Fluorescence detection; Reverse microemulsion
Determination of the natural abundance δ15N of nortropane alkaloids by gas chromatography–isotope ratio mass spectrometry of their ethylcarbamate esters by Katarzyna Kosieradzka; Illa Tea; Emmanuel Gentil; Richard J. Robins (1405-1414).
An important route for the detoxification of tropane alkaloids involves N-demethylation to the nor-compounds followed by further degradation. In order to study the mechanisms of the pertinent reactions, a suitable means to determine the isotope ratios of the substrates and products is required. However, the polarity and functionality of the nortropane compounds makes their analysis as free bases difficult. A method is described which allows both the quantification of nortropane alkaloids and the determination of their natural abundance δ15N values. The protocol exploits the derivatisation of the alkaloids by reaction with ethyl chloroformate in aqueous medium and the quantitative extraction of the ensuing ethylcarbamate esters. The improved chromatographic properties of these derivatives gives ample separation of the isomeric nortropine and norpseudotropine for measurement of their δ15N (‰) values by isotope ratio mass spectrometry interfaced to gas chromatography. Adequate separation could not be achieved with the underivatised compounds. Repeatability and precision are sufficient to allow differences in the δ15N values (∆δ15N) > 0.8‰ to be measured, with a standard deviation routinely ∼0.3‰. The methodology has been tested by determining the changes in the δ15N values of nortropine and norpseudotropine during degradation by cell suspension cultures of a Pseudomonas strain expressing a specific capacity for tropine catabolism. The precision and reproducibility are shown sufficient to allow the evolution of the δ15N values to be followed during the fermentation.
Keywords: Derivatisation; Isotope ratio measurement by mass spectrometry; Nortropine; Reaction mechanism; Tropane alkaloids
DNA–WT1 protein interaction studied by surface-enhanced Raman spectroscopy by Bhuwan Joshi; Ayan Chakrabarty; Christopher Bruot; Hannah Ainsworth; Gail Fraizer; Qi-Huo Wei (1415-1421).
Interactions of proteins with DNA play an important role in regulating the biological functions of DNA. Here we propose and demonstrate the detection of protein–DNA binding using surface-enhanced Raman scattering (SERS). In this method, double-stranded DNA molecules with potential protein-binding sites are labeled with dye molecules and immobilized on metal nanoparticles. The binding of proteins protects the DNA from complete digestion by exonuclease and can be detected by measuring the SERS signals before and after the exonuclease digestion. As a proof of concept, this SERS-based protein–DNA interaction assay is validated by studying the binding of a zinc finger transcription factor WT1 with DNA sequences derived from the promoter of the human vascular endothelial growth factor. Figure A representative dark-field optical microscopic image of Ag nanoparticles attached with dye labeled DNA molecules and two Raman spectra from AAg nanoparticles attached with FAM (left) and TAMRA (right) labeled DNA molecules respectively.
Keywords: SERS; Protein–DNA interactions; Surface plasmons; WT1
Methylene blue as an electrochemical indicator for DF508 cystic fibrosis mutation detection by Hany Nasef; Valerio Beni; Ciara K. O’Sullivan (1423-1432).
Cystic fibrosis is one of the most common life-shortening, childhood-onset inherited diseases. Among the 1,000 known cystic fibrosis-related mutations, DF508 is the most common, with a frequency varying between 50% and 70% according to geographical areas and population typology. In this work, we report the use of methylene blue as an electrochemical reporting agent in the discrimination of synthetic PCR analogue of the DF508 cystic fibrosis mutation (Mut) from the wild type (Wt). At optimum experimental condition, a discrimination factor between mutant and wild type of approximately 1.5-fold was found. The proposed assay was quantitative and linear in the range of 10–100 nM, exhibiting a limit of detection of 2.64 nM. Electrochemical studies at variable ionic strength conditions allowed further elucidation of the mechanism of the methylene blue (MB)–DNA interaction. To the best of our knowledge, this is the first report of detection of hybridisation solely via guanine-specific MB–DNA interaction simultaneously in MB solution, independent of electrostatic interaction as demonstrated in the ionic strength study. The introduction of formamide in the hybridization buffer, to improve discrimination, was also investigated. Finally, mutant wild type discrimination was demonstrated, at 10 nM concentration, with the use of a multi-sensor setup. Figure Electrochemical response before and after sensor regeneration
Keywords: Methylene blue; Cystic fibrosis; DF508; DNA sensor; Electrochemistry
Stability of Se species in plant extracts rich in phenolic substances by Petra Cuderman; Vekoslava Stibilj (1433-1439).
Since there is growing awareness of the strong dependence of the antioxidative function of selenium (Se) upon its chemical form, the stability of Se species during sample preparation is an important factor in obtaining qualitative and quantitative results. Many plant samples are rich in phenolic compounds (antioxidants), but data about their effect on specific Se species in extracts of plant samples are scarce. Therefore, the aim of this study was to investigate the effect of the most common phenolic substances in plant parts, namely tannin and the flavonoid rutin, on the concentration and/or transformation of several Se species (SeMet, SeCys2, SeMeSeCys, Se(VI) and Se(IV)) during sample preparation (24 h incubation at 37 °C) and storage (4 days at 4 °C). Moreover, the effect observed was then studied in a real sample, buckwheat, because this plant is known as a rich source of phenolics, especially tannin and rutin. Se speciation was carried out by on-line coupling of ion-exchange HPLC-ICP-MS after water and enzymatic (protease) hydrolysis. The results showed that the ratio between the two antioxidants has an important role. When the antioxidants were present together, the response for Se(IV) was observed to start to decrease only at a ratio of rutin to tannin of 1:100 (w/w), indicating the ratio between antioxidants in buckwheat seeds. After water extraction, only 40% and after enzymatic extraction 80% of Se(IV) remained, but no other Se compound was detected with the system used. Furthermore, the extracts were not stable during storage at 4 °C. Signals for other Se species were stable. The results obtained for buckwheat seeds showed a decrease in Se(IV) response during sample preparation and storage, comparable to the one obtained with the experiments performed in vitro. However, Se species in extracts of other buckwheat parts (leaves, stems and sprouts) were stable. These results indicate that reactions in the extraction process and during storage may affect Se speciation and may result in misidentifications and inaccurate values.
Keywords: Se species; Phenolic substances; Stability; Buckwheat; HPLC-ICP-MS; Trace elements; Quality assurance/control; Biological samples
Synchrotron FTIR microspectroscopy of the yeast Saccharomyces cerevisiae after exposure to plasma-deposited nanosilver-containing coating by C. Saulou; F. Jamme; C. Maranges; I. Fourquaux; B. Despax; P. Raynaud; P. Dumas; M. Mercier-Bonin (1441-1450).
The present work was focused on elucidating changes in the model yeast Saccharomyces cerevisiae (cell composition, ultrastructure) after exposure to antimicrobial plasma-mediated nanocomposite films. In order to achieve this, a nanosilver-containing coating was deposited onto stainless steel using radiofrequency HMDSO plasma deposition, combined with simultaneous silver sputtering. X-ray photoelectron spectroscopy (XPS) confirmed the presence of silver nanoparticles embedded in an organosilicon matrix. In addition, scanning electron microscopy (SEM) demonstrated the nanoparticle-based morphology of the deposited layer. The antifungal properties towards S. cerevisiae were established, since a 1.4 log reduction in viable counts was observed after a 24-h adhesion compared to control conditions with the matrix alone. Differences in cell composition after exposure to the nanosilver was assessed for the protein region using, for the first time, synchrotron Fourier-transform infrared (FTIR) microspectroscopy of single S. cerevisiae cells, through in situ mapping with sub-cellular spatial resolution. IR spectrum of yeast cells recovered after a 24-h adhesion to the nanosilver-containing coating revealed a significant downshift (20 cm−1) of the amide I peak at 1655 cm−1, compared to freshly harvested cells. This lower band position, corresponding to a loss in α-helix structures, is indicative of the disordered secondary structures of proteins, due to the transition between active and inactive conformations under nanosilver-induced stress conditions. No significant effect on the nucleic acid region was detected. The inhibitory action of silver was targeted against both cell wall and intracellular proteins such as enzymes. Transmission electron microscopy (TEM) observations of the yeast ultrastructure confirmed serious morphological and structural damages. A homogeneous protein-binding distribution of nanosilver all over the cell was assumed, since the presence of electron-dense silver clusters was detected not only on the cell surface but also within the cell. For control experiments with the organosilicon matrix alone, no antimicrobial effect was observed, which was consistent with synchrotron FTIR results and TEM observations.
Keywords: Saccharomyces cerevisiae ; Nanosilver-containing coating; Cold plasma; Antifungal effect; Synchrotron FTIR microspectroscopy; Biological samples; Interface/Surface analysis; IR spectroscopy/Raman spectroscopy; Thin films; Biomaterials; Nanoparticles/Nanotechnology
Identification of biochemical changes in lactovegetarian urine using 1H NMR spectroscopy and pattern recognition by Jingjing Xu; Shuyu Yang; Shuhui Cai; Jiyang Dong; Xuejun Li; Zhong Chen (1451-1463).
A vegetarian diet has been demonstrated to have a profound influence on human metabolism as well as to aid the prevention of several chronic diseases relative to an omnivorous diet. However, there have been no systematic metabolomic studies on all of the biochemical changes induced in human subjects by long-term vegetarianism. In this study, 1H NMR spectroscopy in combination with multivariate statistical analysis was applied to explore the variability in the metabolic urinary profiles of healthy populations from four groups: lactovegetarian male (VEGMALE), lactovegetarian female (VEGFEMALE), omnivorous male (OMNMALE), and omnivorous female (OMNFEMALE). Differences in metabolic profiles were examined in relation to diet and gender by principal component analysis (PCA) and spectral integrals. It was found that the most influential low molecular weight metabolites responsible for the differences between the diet groups were N-acetyl glycoprotein (NAG), succinate, citrate, trimethylamine-N-oxide (TMAO), taurine, glycine, hippurate, phenylalanine, methylhistidine and formate, whereas for the differences in gender groups the most discriminatory metabolites were NAG, succinate, creatinine, arginine, TMAO, taurine, hippurate, mannitol, phenylalanine, and methylhistidine. The results from the PCA of all four groups indicated that diet plays a greater role in influencing metabolite differences than gender. As an exploration, this work shows the potential of metabolomics when applied to nutritional and physiological studies, and it will aid further studies.
Keywords: NMR; Metabolomics; Lactovegetarian; Gender; Principal component analysis; Metabolic profiles
Feasibility study for the rapid screening of target molecules using translational diffusion coefficients: diffusion-ordered NMR spectroscopy of biological toxins by Terry J. Henderson (1465-1471).
A panel of 15 biological toxins ranging between ~60–28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D t. Toxin D t values were measured by pulsed-field gradient 1H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D t values were determined from five independent measurements at both 25 and 37 °C for all toxins in the panel. In the protocol, D t values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within ±0.25 × 10−6 cm2/s of both reference D t values for at least one toxin in the panel. Only solution viscosity was found to influence sample D t measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D t value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to ≤2 possibilities in virtually all cases.
Keywords: Bioanalytical methods; Biomaterials; Forensics/toxicology; NMR/ESR
The effects of abundant plasma protein depletion on global glycan profiling using NanoLC FT-ICR mass spectrometry by Michael S. Bereman; David C. Muddiman (1473-1479).
We report the results of abundant plasma protein depletion on the analysis of underivatized N-linked glycans derived from plasma proteins by nanoLC Fourier-transform ion cyclotron resonance mass spectrometry. N-linked glycan profiles were compared between plasma samples where the six most abundant plasma proteins were depleted (n = 3) through a solid-phase immunoaffinity column and undepleted plasma samples (n = 3). Three exogenous glycan standards were spiked into all samples which allowed for normalization of the N-glycan abundances. The abundances of 20 glycans varying in type, structure, composition, and molecular weight (1,200–3,700 Da) were compared between the two sets of samples. Small fucosylated non-sialylated complex glycans were found to decrease in abundance in the depleted samples (greater than or equal to tenfold) relative to the undepleted samples. Protein depletion was found to marginally effect (less than threefold) the abundance of high mannose, hybrid, and large highly sialylated complex species. The significance of these findings in terms of future biomarker discovery experiments via global glycan profiling is discussed.
Keywords: HILIC; NanoLC FT-ICR MS; Glycan profiling; N-linked glycans; Protein depletion
MALDI-TOF MS stability study of model poly(p-phenylene terephthalamide)s by Anthony P. Gies; Anton Schotman; David M. Hercules (1481-1490).
In the present study, we address the possibility of matrix-assisted laser desorption/ionization (MALDI)–time-of-flight MS analysis-induced chain fragmentation in poly(p-phenylene terephthalamide) (PPD-T) by considering two possible sources: (1) grinding-induced fragmentation resulting from the evaporation–grinding MALDI sample preparation method (E-G method) and (2) in-source/metastable fragmentation induced by the MALDI laser. An analysis of variance (ANOVA) statistical study found, with a high probability, that obtaining MALDI spectra with the effective laser area as large as possible (the “fanned-out” setting) did not cause any chain fragmentation due to the E-G MALDI sample preparation method, even when three additional grinding steps were used. However, the effect of laser fluence was less clear. A significant effect of laser fluence was observed for lower mass oligomers (<1,400 Da), but there was essentially no effect for higher mass species up to our limit of ANOVA measurement (∼2,300 Da). Plausible explanations are presented to explain these observations. The most likely scenario is that “unexpected” end-group modifications occur during PPD-T synthesis, producing small quantities of low mass species, which are amplified by the MALDI-EG extraction procedure. Figure MALDI-TOF MS stability studies indicate that analysis-induced fragmentation, due to sample grinding and laser-induced fragmentation, is not observed.
Keywords: MALDI-TOF MS; ANOVA statistics; Poly(p-phenylene terephthalamide)
Evaluation of microwave-assisted enzymatic digestion and tandem mass spectrometry for the identification of protein residues from an inorganic solid matrix: implications in archaeological research by Stanley M. Stevens Jr; Steve Wolverton; Barney Venables; Andrew Barker; Kent W. Seeley; Prem Adhikari (1491-1499).
A method based on microwave-assisted enzymatic digestion and liquid chromatography–tandem mass spectrometry analysis is presented for the identification of proteins incorporated within solid matrices using protein standards bound to experimental cooking pottery as a validation model. The implementation of microwave irradiation allowed for a significant decrease in overall analysis time in addition to select enhancement of peptide recovery as determined by label-free relative quantitation. We envision that the reported methodology will provide new avenues for scientific discovery in areas such as archaeology and forensics. Results of this series of experiments are part of an ongoing project directed at developing a comprehensive methodology for extracting proteinaceous residues from archaeological pottery.
Keywords: Microwave; Archaeoproteomics; Tandem mass spectrometry; Protein extraction; Forensics; Paleoproteomics
Evaluation of the state-of-the-art measurement capabilities for selected PBDEs and decaBB in plastic by the international intercomparison CCQM-P114 by R. Zeleny; S. Voorspoels; M. Ricci; R. Becker; C. Jung; W. Bremser; M. Sittidech; N. Panyawathanakit; W. F. Wong; S. M. Choi; K. C. Lo; W. Y. Yeung; D. H. Kim; J. Han; J. Ryu; S. Mingwu; W. Chao; M. M. Schantz; K. A. Lippa; S. Matsuyama (1501-1511).
An international intercomparison involving eight national metrology institutes (NMIs) was conducted to establish their current measurement capabilities for determining five selected congeners from the brominated flame retardant classes polybrominated diphenyl ethers and polybrominated biphenyls. A candidate reference material consisting of polypropylene fortified with technical mixtures of penta-, octa- and decabromo diphenyl ether and decabromo biphenyl, which was thoroughly assessed for material homogeneity and stability, was used as study material. The analytical procedures applied by the participants differed with regard to sample pre-treatment, extraction, clean-up, employed calibrants and type of calibration procedure as well as regarding analytical methods used for separation, identification and quantification of the flame retardant congeners (gas chromatography coupled to an electron capture detector (GC-ECD), gas chromatography-mass spectrometry in the electron ionisation mode (GC-EI-MS), gas chromatography-mass spectrometry in the electron capture negative ionisation mode (GC-ECNI-MS), and liquid chromatography-inductive coupled plasma-mass spectrometry (LC-ICP-MS)). The laboratory means agreed well with relative standard deviations of the mean of means of 1.9%, 4.8%, 5.5% and 5.4% for brominated diphenyl ether (BDE) 47, 183 and 209 and for the brominated biphenyl (BB) congener 209, respectively. For BDE 206, a relative standard deviation of 28.5% was obtained. For all five congeners, within-laboratory relative standard deviations of six measurements obtained under intermediate precision conditions were between 1% and 10%, and reported expanded measurements uncertainties typically ranged from 4% to 10% (8% to 14% for BDE 206). Furthermore, the results are in good agreement with those obtained in the characterization exercise for determining certified values for the flame retardant congeners in the same material. The results demonstrate the state-of-the-art measurement capabilities of NMIs for quantifying representative BDE congeners and BB 209 in a polymer. The outcome of this intercomparison (pilot study) in conjunction with possible improvements for employing exclusively calibrants with thoroughly assessed purity suggests that a key comparison aiming at underpinning calibration and measurement capability (CMC) claims of NMIs can be conducted. Figure Mass fraction of deca-brominated diphenyl ether (BDE 209) in the polypropylene study material analysed in the international intercomparison CCQM-P114
Keywords: Flame retardants; Polymer; Polybrominated diphenyl ethers (PBDEs); Polybrominated biphenyls (PBBs); International intercomparison
Applications of LC/ESI-MS/MS and UHPLC QqTOF MS for the determination of 148 pesticides in fruits and vegetables by Jian Wang; Willis Chow; Daniel Leung (1513-1538).
This paper presented the applications of liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) and ultra-high-pressure liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC QqTOF MS) for the determination of 148 pesticides in fruits and vegetables. Pesticides were extracted from fruits and vegetables using a buffered QuEChERS method. Quantification was achieved using matrix-matched standard calibration curves with isotopically labeled standards or a chemical analog as internal standards in an analytical range from 5 to 500 μg/kg. The method performance parameters including overall recovery, intermediate precision, and measurement uncertainty were evaluated according to a statistically designed experiment, i.e., a nested design. For LC/ESI-MS/MS, 95% of the pesticides had recoveries between 81% and 110%; 97% had an intermediate precision ≤20%; and 95% (in fruits) or 93% (in vegetables) showed measurement uncertainty ≤40%. Compared to LC/ESI-MS/MS, UHPLC QqTOF MS showed a relatively poor repeatability and large measurement uncertainty. About 93% (in fruits) or 94% (in vegetables) of the pesticides had recoveries between 81% and 110%; 86% (in fruits) or 90% (in vegetables) had an intermediate precision ≤20%; and 79% (in fruits) or 88% (in vegetables) showed measurement uncertainty ≤40%. LC/ESI-MS/MS proved to be the first choice for quantification or pre-target analysis due to its superior sensitivity and good repeatability. UHPLC QqTOF MS provided accurate mass measurement and isotopic patterns, and was an ideal tool for post-target screening and confirmation.
Keywords: LC/ESI-MS/MS; UHPLC QqTOF; Pesticides; Fruits; Vegetables; Measurement uncertainty
Fate of antibacterial spiramycin in river waters by P. Calza; S. Marchisio; C. Medana; C. Baiocchi (1539-1550).
Spiramycin, a widely used veterinary macrolide antibiotic, was found at traceable levels (nanograms per litre range) in Po River water (N-Italy). The aqueous environmental fate of this antibiotic compound was studied through drug decomposition, the identification of the main and secondary transformation products (TPs), assessment of mineralisation and the investigation of drug TPs toxicity. Initially, laboratory experiments were performed, with the aim of stimulating the antibacterial transformation processes followed in aquatic systems. The TPs were identified through the employment of the liquid chromatography (LC)-mass spectrometry technique. Under illumination, spiramycin degraded rapidly and transformed into numerous organic (intermediate) compounds, of which 11 could be identified, formed through five initial transformation routes. These laboratory simulation experiments were verified in situ to check the mechanism previously supposed. Po River water was sampled and analysed (by LC-high-resolution mass spectrometry) at eight sampling points. Among the previously identified TPs, five of them were also found in the river water. Three of them seem to be formed through a direct photolysis process, while the other two are formed through indirect photolysis processes mediated by natural photo sensitisers. The transformation occurring in the aquatic system involved hydroxylation, demethylation and the detachment of forosamine or mycarose sugars. Toxicity assays using Vibrio fischeri proved that even if spiramycin did not exhibit toxicity, its transformation proceeded through the formation of toxic products.
Keywords: Spiramycin; Antibiotics; Photochemistry; Transformation products; River water; Toxicity
Sensitive determination of fluoroquinolone residues in waters by capillary electrophoresis with laser-induced fluorescence detection by Manuel Lombardo-Agüí; Laura Gámiz-Gracia; Ana M. García-Campaña; Carmen Cruces-Blanco (1551-1557).
A sensitive capillary electrophoresis –laser-induced fluorescence method has been developed for the determination of six fluoroquinolones of human (ofloxacin, lomefloxacin, and norfloxacin) and veterinary use (danofloxacin, enrofloxacin, and sarafloxacin) in different kinds of water. Fluorescence detection was achieved using a He-Cd laser, with a wavelength of 325 nm. Separation was performed in a fused-silica capillary, and conditions were optimized to obtain the most adequate separation and with the best sensitivity. The separation was carried out in a 70-cm-long capillary (75 μm internal diameter, effective length 55 cm) by using a 125 mM phosphoric acid separation buffer at pH 2.8, with 36% of methanol. The water sample pretreatment involved the separation and preconcentration of the analytes by solid phase extraction. Two reverse-phase cartridges have been evaluated, namely Oasis hydrophilic–liphophilic balance and Strata-X; the latter provided the best recoveries for the selected analytes. The method shows very low detection limits (0.3–1.9 ng/L) with acceptable recoveries and precisions and has been successfully applied to the analysis of well and tap water samples.
Keywords: Capillary electrophoresis; Fluoroquinolones; Laser-induced fluorescence; SPE; Water samples
Advances in identification of plant gums in cultural heritage by thermally assisted hydrolysis and methylation by Chiara Riedo; Dominique Scalarone; Oscar Chiantore (1559-1569).
Plant gums are present in works of art as binding media for watercolours and adhesives for cellulosic substrates. Thermally assisted hydrolysis and methylation (THM) in combination with analytical pyrolysis coupled to GC/MS has been applied to the characterisation of plant gums typically used in artworks. THM products from standard samples of arabic gum, tragacanth gum and cherry gum were characterised. The main products identified are permethylated and partially methylated aldonic acids, characteristic of specific epimeric sugars. Aldonic acids were formed by alkaline hydrolysis of free reducing sugars and of reducing polysaccharide terminal groups, while methylation occurs during pyrolysis. The presence of these characteristic markers allows gum identification. A systematic analysis of all the parameters that can affect the marker yields was performed. In particular, the influence of pyrolysis temperature, reagent concentration and contact time between tetramethylammonium hydroxide and sample were studied, and different kinds of sample preparation procedures were tested. Some analyses on real watercolours were performed, and gum binders were classified using the peak area ratio of the main monosaccharide markers. Figure Classification of gums on the basis of marker area peaks ratio
Keywords: Plant gum; Pyrolysis; Thermally assisted hydrolysis and methylation; Gas chromatography/mass spectrometry; Cultural heritage; Watercolours
Evaluation of migration behaviour of therapeutic peptide hormones in capillary electrophoresis using polybrene-coated capillaries by Ghiulendan Aptisa; Fernando Benavente; Victoria Sanz-Nebot; Elisabeta Chirila; José Barbosa (1571-1579).
Modelling electrophoretic mobility as a function of pH can be simultaneously used for determination of ionization constants and for rapid selection of the optimum pH for separation of mixtures of the modelled compounds. In this work, equations describing the effect of pH on electrophoretic behaviour were used to investigate migration of a series of polyprotic amphoteric peptide hormones between pH 2 and 12 in polybrene-coated capillaries. Polybrene (hexadimethrin bromide) is a polymer composed of quaternary amines that is strongly adsorbed by the fused-silica inner surface, preventing undesired interactions between the peptides and the inner capillary wall. In polybrene-coated capillaries the separation voltage must be reversed, because of the anodic electroosmotic flow promoted by the polycationic polymer attached to the inner capillary wall. The possibility of using polybrene-coated capillaries for determination of accurate ionization constants has been evaluated and the optimum pH for separation of a mixture of the peptide hormones studied has been selected. Advantages and disadvantages of using bare fused-silica and polybrene-coated capillaries for these purposes are discussed.
Keywords: Capillary electrophoresis; Coated capillary; Dissociation constant; Hexadimethrin bromide; Peptide; prediction
Study on elution behavior of poly(amidoamine) dendrimers and their interaction with bovine serum albumin in asymmetrical flow field-flow fractionation by Seungho Lee; Hai Doo Kwen; Sung Kwang Lee; Sachin Vilas Nehete (1581-1588).
Polyamidoamine (PAMAM) dendrimers have an amine surface and an ethylenediamine core and are of great interest in various applications such as in drug delivery. Physiochemical properties of PAMAM dendrimers vary with pH. At neutral to basic pH, PAMAM dendrimers are either weakly charged or uncharged and tend to adsorb on to the neutral packing material, making chromatographic separation of the dendrimers difficult. Asymmetrical flow field-flow fractionation (AsFlFFF) was tested as an alternative to the chromatographic techniques for separation of the PAMAM dendrimers. AsFlFFF provided generation-based separation of the dendrimers even at neutral and basic pH. The elution time increased gradually as the generation number (and thus the size) increased. Separation of impurities such as generational or missing-arm impurities and aggregates from the main population was also achieved. Electrostatic and hydrophobic interactions (e.g., repulsive elecrostatic interaction among the dendrimer molecules or attractive hydrophobic interaction between the dendrimer molecules and the membrane) may result in an inaccurate size measurement. Careful optimization of experimental conditions such as the flow rate, pH, and the salt concentration may be required to minimize the interactions with the membrane. AsFlFFF was also tested for a study on the interaction between the PAMAM dendrimers and proteins. AsFlFFF was able to show the growth in the size of bovine serum albumin (BSA) when BSA is mixed with increasing amounts of PAMAM dendrimers. Results suggest that, with proper optimization, AsFlFFF could become a useful tool for separation and characterization of large charged molecules such as PAMAM dendrimers.
Keywords: PAMAM dendrimers; Asymmetrical flow field-flow fractionation; Separation; Interaction; Hydrodynamic diameter
Determining the absolute, chemical-heterogeneity-corrected molar mass averages, distribution, and solution conformation of random copolymers by Imad A. Haidar Ahmad; André M. Striegel (1589-1598).
We present a method by which to obtain the absolute, chemical-heterogeneity-corrected molar mass (M) averages and distributions of copolymers and apply the method to a gradient random copolymer of styrene and methyl methacrylate in which the styrene percentage decreases from approximately 30% to 19% as a function of increasing molar mass. The method consists of separation by size-exclusion chromatography (SEC) with detection using multi-angle static light scattering (MALS), differential viscometry (VISC), differential refractometry (DRI), and ultraviolet absorption spectroscopy (UV) and relies on the preferential absorption of styrene over methyl methacrylate at 260 nm. Using this quadruple-detector SEC/MALS/UV/VISC/DRI approach, the percentage of styrene (%St) in each elution slice is determined. This %St is then used to determine the specific refractive index increment, corrected for chemical composition, at each elution slice, which is then used to obtain the molar mass at each slice, corrected for chemical composition. From this corrected molar mass and from the chemical-composition-corrected refractometer response, the absolute, chemical-heterogeneity-corrected molar mass averages and distribution of the copolymer are calculated. The corrected molar mass and intrinsic viscosity at each SEC elution slice are used to construct a chemical-heterogeneity-corrected Mark–Houwink plot. The slice-wise-corrected M data are used, in conjunction with the MALS-determined R G,z of each slice, to construct a conformation plot corrected for chemical heterogeneity. The corrected molar mass distribution (MMD) of the gradient copolymer extends over an approximately 30,000 g/mol wider range than the uncorrected MMD. Additionally, correction of the Mark–Houwink and conformation plots for the effects of chemical heterogeneity shows that the copolymer adopts a more compact conformation in solution than originally concluded. Figure Table of Contents Graphic
Keywords: Chemical heterogeneity; Copolymers; Multi-detector size-exclusion chromatography; Molar mass; Solution conformation
Influence of salt ions on binding to molecularly imprinted polymers by Henrik Kempe; Maria Kempe (1599-1606).
Salt ions were found to have an influence on template binding to two model molecularly imprinted polymers (MIPs), targeted to penicillin G and propranolol, respectively, in water–acetonitrile mixtures. Water was detrimental to rebinding of penicillin G whereas propranolol bound in the entire water–acetonitrile range tested. In 100% aqueous solution, 3-M salt solutions augmented the binding of both templates. The effects followed the Hofmeister series with kosmotropic ions promoting the largest increase. Binding was mainly of a non-specific nature under these conditions. In acetonitrile containing low amounts of water, the specific binding to the MIPs increased with the addition of salts. Binding of penicillin G followed the Hofmeister series while an ion-exchange mechanism was observed for propranolol. The results suggest that hydration of kosmotropic ions reduces the water activity in water-poor media providing a stabilizing effect on water-sensitive MIP–template interactions. The effects were utilized to develop a procedure for molecularly imprinted solid-phase extraction (MISPE) of penicillin G from milk with a recovery of 87%. Figure Binding augmentation to a penicillin G imprinted MIP at the addition of kosmotropic ions.
Keywords: Hofmeister effect; Molecular imprinting; Molecular recognition; Penicillin G; Propranolol; Solid-phase extraction
Microwave-assisted sol–gel synthesis for molecular imprinting by Liang Feng; Barathi Pamidighantam; Paul C. Lauterbur (1607-1612).
Molecularly imprinted polymers have been the subject of intense research for several decades in both academic and industrial settings. In this paper, we introduce a novel microwave-assisted sol–gel method for molecular imprinting of silica microspheres. The microspheres were characterized, and their adsorption of imprint and non-imprint molecules was investigated. The dye molecules methyl orange and ethyl orange were used as templates. Good molecular imprinting was observed as evaluated by the re-adsorption of dye into the silica matrix followed by the removal of dye from the supernatant solution. We describe a novel microwave-assisted sol-gel method for molecular imprinting of silica microspheres. The microspheres were smooth and well dispersed. The adsorption capacity, relative adsorption capacity, specific adsorption capacity, and different effects for imprinted and non-imprinted microspheres were determined for dye molecules as the molecular imprints. This synthetic methodology has promise for use in preparation of molecularly imprinted solids
Keywords: Molecular imprinting; Microwave-assisted; Sol–gel
Erratum to: Signal limitations in tip-enhanced Raman scattering: the challenge to become a routine analytical technique by Samuel Berweger; Markus B. Raschke (1613-1613).