Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.378, #6)
Analytical applications of NMR diffusion measurements
by Kristin E. Price; Laura H. Lucas; Cynthia K. Larive (pp. 1405-1407).
Expanding your laboratory by accessing collaboratory resources
by David W. Hoyt; Sarah D. Burton; Michael R. Peterson; James D. Myers; George Chin Jr (pp. 1408-1410).
Research involving NMR spectroscopy at undergraduate institutions in the United States
by Thomas J. Wenzel (pp. 1411-1413).
Characterization of n-butyl acrylate centered triads in poly(n-butyl acrylate-co-carbon monoxide-co-ethylene) by isotopic labeling and two dimensional NMR by Masud Monwar; Sung Joon Oh; Peter L. Rinaldi; Elizabeth F. McCord; Robin A. Hutchinson; Michael M. Buback; Henning Latz (pp. 1414-1427).
Poly(n-butylacrylate-co-carbon monoxide-co-ethylene) (polyEBC) samples prepared from 13C-labeled monomer, n-butyl acrylate, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex structure of the terpolymer, 2D-1H/13C-heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced resonances in the spectra of two polymer samples, one polymer resulting from synthesis with 1-13C-n-butylacrylate monomer and a second polymer obtained from a synthesis with 2-13C-n-butylacrylate monomer. High-resolution 2D-NMR combined with 13C-labeling of the polymer greatly simplifies the 2D-NMR spectra, selectively enhances the weak peaks from low occurrence B-centered triad structures, and aids in their resonance assignments. In all experiments, the sample temperature was 120 °C, to ensure a homogeneous solution and sufficient molecular mobility.
Keywords: Polymer NMR; 2D-NMR; 13C-labeling; Polyethylene
Determination of microscopic acid–base parameters from NMR–pH titrations by Zoltán Szakács; Márta Kraszni; Béla Noszál (pp. 1428-1448).
The theory and practice of proton microspeciation based on NMR–pH titrations are surveyed. Principles of bi-, tri-, tetra-, and n-protic microequilibrium systems are discussed. Evaluation methods are exemplified by case studies on bi- and tetraprotic biomolecules. Selection criteria and properties of ‘reporter’ NMR nuclei are described. Literature data on complete microspeciations of small ligands and site-specific basicity characterizations of peptides and proteins are critically reviewed.
Keywords: Microscopic protonation constant; NMR–pH titration; Chemical shift; Microspeciation
Determination of rotamer populations and related parameters from NMR coupling constants: a critical review by Márta Kraszni; Zoltán Szakács; Béla Noszál (pp. 1449-1463).
Methods to determine rotamer populations from NMR homo- and heteronuclear vicinal coupling constants are reviewed. Theory and practice related to the elucidation of various gauche and trans limiting coupling constants as key parameters in the characterization of discrete rotational isomers are discussed. Properties and capacities of Karplus-type equations are assessed. Continuous models of rotational isomerism are compared to discrete ones. Principles of the highly specific physicochemical parameters rotamer-specific basicity and rotamer-specific partition coefficient are also described.
Keywords: Rotamer population; Vicinal coupling constant; Trans and gauche coupling; Karplus equation; Rotamer-specific basicity; Rotamer-specific partition
Recent developments in the 13C NMR spectroscopic analysis of paramagnetic hemes and heme proteins by Mario Rivera; Gregori A. Caignan (pp. 1464-1483).
Despite the wealth of information that has been obtained from the study of paramagnetic hemes and heme proteins by 1H NMR spectroscopy, there are certain limitations imposed by the nature of paramagnetically affected resonances that are difficult to overcome. Although it has long been recognized that 13C NMR spectroscopy is likely to be a powerful complementary technique to overcome some of these limitations, the low sensitivity and low natural abundance of 13C nuclei has resulted in a lag in the application of 13C NMR spectroscopy to the study of paramagnetic hemes and heme proteins. The tremendous advances in methodology and instrumentation witnessed in the NMR field, coupled to the advent of recombinant DNA methods that have made possible the preparation and purification of significant quantities of proteins, and the biosynthesis of 13C-labeled heme, have contributed to an increased interest in the study of paramagnetic heme active sites by 13C NMR spectroscopy. As a consequence, 13C NMR spectroscopy is emerging as a powerful tool to study heme electronic structure and structure–function relationships in heme-containing proteins. In this report we strive to summarize some of the recent developments in the analysis of paramagnetic hemes and heme-containing proteins by 13C NMR spectroscopy.
Coupling NMR to NOM by Robert L. Cook (pp. 1484-1503).
This work itemizes and critically assesses several 1D and multi-dimensional nuclear magnetic resonance (NMR) techniques, in both the liquid (solvent suppression, APT, DEPT, INEPT, COSY, TOCSY, HSQC, HMQC, HMBC, NOESY, ROESY and others) and solid states (DP, SACP, RAMP-CP, CP-TOSS, MQ-DEPT, 2D 1H–13C HETCOR and others), which are relevant to the characterization of natural organic matter (NOM). The pros and cons of many of the discussed techniques are compared in an effort to provide guidance to the most beneficial utilization of these NMR instrumental techniques for researchers interested in gaining insight into various aspects of NOM.
Keywords: Natural organic matter; Humic acid; Fulvic acid; Solid state; Liquid state; Multi-dimensional; Nuclear magnetic resonance
Solid-state NMR studies of pharmaceutical solids in polymer matrices by Joseph W. Lubach; Brian E. Padden; Stephanie L. Winslow; Jonathon S. Salsbury; David B. Masters; Elizabeth M. Topp; Eric J. Munson (pp. 1504-1510).
Biodegradable drug-delivery systems can be formulated to release drug for hours to years and have been used for the controlled release of medications in animals and humans. An important consideration in developing a drug-delivery matrix is knowledge of the long-term stability of the form of the drug and matrix after formulation and any changes that might occur to the drug throughout the delivery process. Solid-state NMR spectroscopy is an effective technique for studying the state of both the drug and the matrix. Two systems that have been studied using solid-state NMR spectroscopy are presented. The first system studied involved bupivacaine, a local anesthetic compound, which was incorporated into microspheres composed of tristearin and encapsulated using a solid protein matrix. Solid-state 13C NMR spectroscopy was used to investigate the solid forms of bupivacaine in their bulk form or as incorporated into the tristearin/protein matrix. Bupivacaine free base and bupivacaine-HCl have very different solid-state NMR spectra, indicating that the molecules of these compounds pack in different crystal forms. In the tristearin matrix, the drug form could be determined at levels as low as 1:100 (w/w), and the form of bupivacaine was identified upon loading into the tristearin/protein matrix. In the second case, the possibility of using solid-state 13C NMR spectroscopy to characterize biomolecules lyophilized within polymer matrices is evaluated by studying uniformly 13C-labeled asparagine (Asn) in 1:250 (w/w) formulations with poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA). This work shows the capability of solid-state NMR spectroscopy to study interactions between the amino acid and the polymer matrix for synthetic peptides and peptidomimetics containing selective 13C labeling at the Asn residue.
Keywords: Solid-state NMR; CP/MAS; Polymer; Drug–excipient interactions; 13C Labeling
Metabolic profiling of normal and hypertensive rat kidney tissues by hrMAS-NMR spectroscopy by Stephen D. Huhn; Christina M. Szabo; Jerome H. Gass; Adriana E. Manzi (pp. 1511-1519).
Intact kidney tissue samples of normal and spontaneously hypertensive rats (SHRs) were analyzed by hrMAS-NMR spectroscopy and principal component analysis (PCA). Radial components (cortex, outer stripe of the outer medulla, inner stripe of the outer medulla, and papilla) were sampled from various regions across the kidney from multiple animals in order to establish inter- and intra-animal variability. The effects of temperature were also measured. Papilla was differentiated from the other tissue types, and this variation by tissue type was greater than the effect of temperature on the samples (spectra were compared from samples at 2 and 30 °C). This study also revealed long term stability issues of tissue storage at -80 °C. The PCA showed that the greatest differentiation between normal rats and SHRs was found in the cortex and the regions in the NMR spectra that were correlated with this variation were identified.
Keywords: High-resolution magic angle spinning; NMR; Principal component analysis; Metabonomics; Spontaneously hypertensive rats; Hypertension; Kidney tissues
NMR difference spectroscopy with a dual saddle-coil difference probe by Megan A. Macnaughtan; Aaron P. Smith; Peter B. Goldsbrough; Robert E. Santini; Daniel Raftery (pp. 1520-1527).
A new difference probe for nuclear magnetic resonance (NMR) spectroscopy is presented. The difference probe uses two saddle-shaped coils to excite and detect two samples simultaneously. The samples are held in a specially modified 3-mm NMR tube with an Ultem plastic disk to separate the samples. The probe’s resonant circuit contains two crossed diodes that passively switch the relative phase of each coil during the NMR experiment. The result is a difference spectrum from the two samples. The degree of cancellation of common signals was determined to be approximately 90%, and the application of the probe to relaxation-edited difference spectroscopy for identifying protein–ligand interactions was demonstrated using glutathione and glutathione S-transferase binding protein.
Keywords: Difference spectroscopy; Background subtraction; Saddle coils; Protein–ligand interactions; Relaxation
Chiral separation of nanomole amounts of alprenolol with cITP/NMR by Dimuthu A. Jayawickrama; Jonathan V. Sweedler (pp. 1528-1535).
On-line cITP–NMR with chiral selectors separates and concentrates analytes and identifies host–guest interactions of analytes with selectivity enhancers in the electrolyte. An NMR microcoil designed for a 200 μm i.d. capillary creates a high-mass-sensitivity 30 nL NMR cell and is used as an on-line detector for cITP. Using a mixture of 2 nmol racemic alprenolol in acetate buffer with α-cyclodextrin and sulfated β-cyclodextrin at pD 6.0, cITP–NMR successfully separates and concentrates both R- and S-alprenolol. The concentration enhancement for the R isomer is 224-fold and for the S isomer is 200-fold. The estimated concentration at peak maximum for R-alprenolol is ~28 mmol L−1 and a slightly lower concentration, 25 mmol L−1 is achieved for S-alprenolol. These concentrations convert to placing 76% of the injected S-alprenolol and 84% of the R-alprenolol into the 30 nL detection cell at peak maximum. With on-flow cITP–NMR, intermolecular interactions between the cyclodextrins and the alprenolol are observed in the NMR spectra. Aromatic and methyl moieties of R- and S-alprenolol are identified as two important sites that bind with these particular cyclodextrins.
Keywords: Chiral separation; Capillary isotachophoresis; Microcoil NMR; On-flow
Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes by Thomas J. Wenzel; Bailey E. Freeman; David C. Sek; Jason J. Zopf; Takashi Nakamura; Jin Yongzhu; Keiji Hirose; Yoshito Tobe (pp. 1536-1547).
Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in 1H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown–substrate mixtures in methanol-d4 causes shifts in the spectra of substrates and often enhances the chiral discrimination in the 1H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.
Keywords: Crown ether; Chiral recognition; Enantiomeric discrimination; NMR spectroscopy; Lanthanide
A Bloembergen–Purcell–Pound 13C NMR relaxation study of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate by W. R. Carper; P. G. Wahlbeck; J. H. Antony; D. Mertens; A. Dölle; P. Wasserscheid (pp. 1548-1554).
The molecular structure and rotational motion of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were studied over a wide temperature range using the Bloembergen–Purcell–Pound 13C NMR spin–lattice relaxation method and NOE factors. Examination of the spin–lattice relaxation times (T 1) and the rates (R 1=1/T 1) of the 1-butyl-3-methylimidazolium cation reveals the relative motions of each carbon in the imidazolium cation. The rotational characteristics of the [BMIM] cation are supported by ab-initio molecular structures of [BMIM][PF6] using density functional theory (DFT) and Hartree–Fock (HF) methods. The ab-initio gas phase structures of [BMIM][PF6] indicate that the 1-butyl-3-methylimidazolium C2 hydrogen, the ring methyl group, and the butyl side-chain hydrogen atoms form hydrogen bonds with the hexafluorophosphate anion.
Keywords: NMR relaxation; Ionic liquid; Ab-initio calculations
The pH-dependence of preferential solvation as studied by intermolecular homo- and heteronuclear NOE measurements of adenosine in water–trifluoroethanol mixtures by Manuel Angulo; Stefan Berger (pp. 1555-1560).
A study of the state of solvation of the adenine ring in adenosine and adenosine 5′-monophosphate disodium salt in water and in a (7.5:2.5) water–TFE mixture has been carried out by measurement of homo- and heteronuclear intermolecular NOE enhancements between water or TFE and the aromatic protons of these compounds. The results give evidence of site specificity in solute–solvent interaction for both solvent systems and preferential solvation of the solute by TFE in the water–TFE mixture. Significant pH dependence of these interactions has been discovered.
Keywords: NMR; Intermolecular NOE; Preferential solvation; pH dependence; Trifluoroethanol; Adenosine
Characterization of the selenotrisulfide formed by reaction of selenite with end-capped phytochelatin-2 by Stephen M. Spain; Dallas L. Rabenstein (pp. 1561-1567).
The phytochelatins are a family of peptides synthesized by plants in response to exposure to heavy metals and metalloids, including selenium in the form of selenite. The amino acid sequence of the phytochelatin (PC) peptides is (γ-Glu-Cys) n -Gly, where n typically ranges from 2 to 5. In this paper, the products of the reaction of selenite with an end-capped analogue of PC2, Ac-(γ-Glu-Cys)2-Gly-NH2, are characterized. Selenite reacts with Ac-(γ-Glu-Cys)2-Gly-NH2 (Ac-PC2-NH2) to form a compound that contains an intramolecular selenotrisulfide (-SSeS-)-linkage (Se[Ac-PC2-NH2]) and oxidized Ac-PC2-NH2. Both Se[Ac-PC2-NH2] and oxidized Ac-PC2-NH2 were isolated by HPLC and were characterized by MALDI–TOF mass spectrometry, by two-dimensional 1H and 13C NMR and, in the case of Se[Ac-PC2-NH2], by 77Se NMR. Using dihedral angles determined from vicinal 1H–1H coupling constants as constraints for the conformations around the CysCαH–CysCβH bonds, structures were predicted for the most abundant form of both compounds by Monte Carlo molecular mechanics simulations.
Keywords: Phytochelatins; Selenium; Selenotrisulfide; Peptide; NMR
NMR measurements of diffusion in concentrated samples: avoiding problems with radiation damping by Mark A. Connell; Adrian L. Davis; Alan M. Kenwright; Gareth A. Morris (pp. 1568-1573).
Pulsed field gradient spin echo NMR is generally the method of choice for diffusion measurements on liquid samples. With modern high field instruments, however, severe problems can arise when it is applied to samples with very high proton concentrations because of the presence of radiation damping. The problems may be greatly reduced by a suitable choice of experimental parameters, in particular the use of modified stimulated echo pulse sequences with a reduced flip angle for the first pulse.
Keywords: Diffusion; Radiation damping; DOSY; Water; Siloxanes
Tools and strategies for processing diffusion-ordered 2D NMR spectroscopy (DOSY) of a broad, featureless resonance: an application to methylaluminoxane (MAO) by Jan Lasse Eilertsen; Randall W. Hall; Larry S. Simeral; Leslie G. Butler (pp. 1574-1578).
DOSY has been extremely successful in many studies of molecular weight distributions, especially when the components are separable along the chemical shift axis. However, an unresolved NMR resonance yields the familiar problem of overlapping exponential decays. In a study of methylaluminoxane (MAO), a set of data processing and simulation tools were developed: read Bruker data files (Matlab); preliminary non-linear least-squares fit with f-test (Matlab); movie generation of the fits (Matlab); conversion of diffusion coefficients to molecular masses through molecular volumes (Gaussian-98); and simulation of DOSY data sets for various molecular mass distributions (Mathematica). These tools are presented here and briefly compared with other DOSY analysis methods.
Keywords: DOSY; Methylaluminoxane; MAO; Levenberg–Marquardt; Movie; Molecular volume
Characterization of humic substances: Implications for trihalomethane formation by Ceyda Senem Uyguner; Christine Hellriegel; William Otto; Cynthia K. Larive (pp. 1579-1586).
Humic substances are precursors of carcinogenic trihalomethanes (THMs) formed during disinfection by chlorination in water treatment processes. In an effort to understand the relationship between trihalomethane formation potential (THMFP) and physicochemical properties of humic substances, UV-visible absorbance, fluorescence in emission and synchronous scan modes, and NMR spectra were measured for several aquatic fulvic and humic acids. For comparison, a soil fulvic acid was also examined using these methods. The feasibility of the gradient modified spin-echo (GOSE) NMR experiment to selectively measure singlet resonances arising from isolated protons was examined. In addition, diffusion coefficients were measured for DMSO solutions of the fulvic acids using BPPLED and GOSE-edited pulse sequences. Although none of the methods tested produced results that correlated with THMFP, the GOSE intensities determined for different regions of the NMR spectra did reflect the relative abundance of different types of functional groups produced by lignin oxidation. In addition, the GOSE-edited diffusion results suggest that the isolated protons, those most reactive to chlorination, are more likely contained in the larger molecular weight fractions of fulvic acids.
Keywords: Humic substances; NMR; THM; Trihalomethane; Disinfection byproducts
A generic sandwich-type biosensor with nanomolar detection limits by Antje J. Baeumner; Caroline Jones; Ching Yee Wong; Andrew Price (pp. 1587-1593).
A quantitative and highly sensitive, yet simple and rapid, biosensor system was developed for the detection of nucleic acid sequences that can also be adapted to the detection of antigens. A dipstick-type biosensor with liposome amplification, based on a sandwich assay format with optical detection, was combined with a simple coupling reaction that allows the transformation of the generic biosensor components to target specific ones by a mere incubation step. This biosensor platform system was developed and optimized, and its principle was proven using DNA oligonucleotides that provided a nucleic acid biosensor for the specific detection of RNA and DNA sequences. However, the coupling reaction principle chosen can also be used for the immobilization of antibodies or receptor molecules, and therefore for the development of immunosensors and receptor-based biosensors. The generic biosensor consists of liposomes entrapping sulforhodamine B that are coated with streptavidin on the outside, and polyethersulfone membranes with anti-fluorescein antibodies immobilized in the detection zone. In order to transform the generic biosensor into a specific DNA/RNA biosensor, two oligonucleotides that are able to hybridize to the target sequence were labeled with a biotin and a fluorescein molecule, respectively. By simultaneously incubating the liposomes, both oligonucleotides, and the target sequence in a hybridization buffer for 20–30 min at 42 °C, a sandwich complex was formed. The mixture was applied to the polyethersulfone membrane. The complex was captured in the detection zone and quantified using a handheld reflectometer. The system was tested using RNA sequences from B. anthracis, C. parvum and E. coli. Quantitation of concentrations between 10 fmol and 1000 fmol (10–1000 nM) was possible without altering any biosensor assay conditions. In addition, no changes to hybridization conditions were required when using authentic nucleic acid sequence-based amplified RNA sequences, and the generic biosensor compared favorably with those previously developed specifically for the RNA sequences. Therefore, the universal biosensor described is an excellent tool, for use in laboratories or at test sites, for rapidly investigating and quantifying any nucleic acid sequence of interest, as well as potentially any antigen of interest that can be bound by two antibodies simultaneously.
Keywords: Biosensor; Nucleic acid; Antibody; Detection; Nanomolar
Functionalised electrode array for the detection of nitric oxide released by endothelial cells using different NO-sensing chemistries by Joshua Oni; Alain Pailleret; Sonnur Isik; Nizam Diab; Ina Radtke; Andrea Blöchl; Michael Jackson; Fethi Bedioui; Wolfgang Schuhmann (pp. 1594-1600).
In a preliminary study aimed at developing strategies for the simultaneous detection of various biologically important molecules, a procedure is described that allows the electrochemical detection of nitric oxide (NO) released by a population of human umbilical vein endothelial cells (HUVEC) by using an array of electrodes comprising three individually addressable electrodes. Each electrode in the array was modified with a different NO-sensitive electrocatalyst, thereby demonstrating the possibility of modifying the individual electrodes in an array with different sensing chemistries. This study opens a doorway to the development of arrays of electrodes for the simultaneous detection of multiple analytes in a complex environment by suitably tailoring the sensitivity and selectivity of each electrode in the array to a specific analyte in the test medium.
Keywords: Nitric oxide; Electrodes array; Electrocatalysis; Chemically modified electrodes; HUVEC
Fourier-transform infrared spectroscopic study of the interactions of selenium species with living bacterial cells by J. C. Feo; M. A. Castro; L. C. Robles; A. J. Aller (pp. 1601-1607).
A study of the interactions of several selenium species with living bacterial cells was carried out by Fourier-transform infrared (FT-IR) spectroscopy. Bacterial cells consisted of an Escherichia coli strain (K-12) cultivated in a growth medium based on glucose contaminated with selenium species. Equilibrium between the analyte in the solution and the extraction medium was established, and then the effects of selenium species upon the external membrane of the living bacterial cells were characterized by performing FT-IR spectroscopy of whole cells. The presence of the toxicants at various concentrations in the culture medium had an effect on the FT-IR spectra, and the concentration of the selenium species was determined directly in the biomass by FT-IR spectroscopy. The intensity ratios between several absorption lines, which varied as a function of the concentration of the selenium species, were used as the analytical signal.
Keywords: Speciation; Selenium species; Selenomethionine; Selenoethionine; Living bacterial cells; Fourier-transform infrared spectroscopy
Application of laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP–MS) to investigate trace metal spatial distributions in human tooth enamel and dentine growth layers and pulp by Daniel Kang; Dulasiri Amarasiriwardena; Alan H. Goodman (pp. 1608-1615).
Human tooth enamel provides a nearly permanent and chronological record of an individual’s nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196×339 μm2 raster pattern areas (6.6×104 μm2) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine–enamel junction (DEJ), dentine, and the dentine–pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. 43Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA–ICP–MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.
Keywords: Human teeth; Trace metals; Enamel growth layers; Micro spatial distribution; Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS)
Analysis and interpretation of data from real-time PCR trace detection methods using quantitation of GM soya as a model system by Malcolm J. Burns; Hernan Valdivia; Neil Harris (pp. 1616-1623).
Recent years have seen an increased interest in DNA trace detection methods involved in many areas of bioanalytical research, such as quantitation of genetically modified (GM) ingredients in food products. There is little in the way of standardisation of data handling from these methods, and the data generated needs to be analysed appropriately if the results are to be interpreted correctly. This paper describes particular aspects of real-time PCR trace detection methods in order to increase the understanding of data generated using this bioanalytical technique. Using the specific example of GM soya detection and quantitation, it focuses on the production of calibration curves based on the mean and individual data values, the interpretation of correlation coefficients, regression techniques, and discusses suitable data analysis arising from simple and more complex experimental designs following transformation. By using the approaches outlined in this paper, more accurate analysis of data from real-time PCR and GM trace detection methods could be achieved.
Keywords: Real-time PCR; Trace detection; Data analysis; Quality assurance
Determination of the absolute configuration of selenomethionine from antarctic krill by RP-HPLC/ICP-MS using chiral derivatization agents by Jan Bergmann; Stephan Lassen; Andreas Prange (pp. 1624-1629).
A fast and sensitive method was developed for the determination of the absolute configuration of selenomethionine. The enantiomers of selenomethionine were converted into diastereomeric isoindole derivatives by reaction with o-phthaldialdehyde and N-isobutyryl-l-cysteine. This easy-to-handle reaction proceeds quantitatively in a few minutes at room temperature. Separation and detection of the diastereomers was achieved by reversed-phase high-performance liquid chromatography–inductively coupled plasma-mass spectrometry (RP-HPLC/ICP-MS) using a conventional C18 reversed-phase column. Detection limits of about 4 µg L−1 were obtained. The method was applied to the determination of the configuration of selenomethionine extracted from antarctic krill, which turned out to possess the l-configuration.
Keywords: Selenomethionine; Chiral speciation; Enantiomer separation; Inductively coupled plasma mass spectrometry; Krill
Determination of trace elements in wines and classification according to their provenance by Gabriela Thiel; Georg Geisler; Ines Blechschmidt; Klaus Danzer (pp. 1630-1636).
Provenance and authenticity of wines can be recognized on the basis of typical mineral and trace element patterns by means of chemometric methods. Therefore analytical methods were developed for the determination of As, Be, Co, Cs, Ga, Li, Nb, Ni, Rb, Te, Ti, W, Y, and Zr as well as Mo, Cd, Sb, Tl, U, and the rare earth elements in wines by inductively coupled plasma mass spectrometry (ICP-MS). For low risk of contamination or loss of analyte as well as depletion of sample amount and an easy sample pretreatment, direct measurement of diluted wines was studied. The accuracy of the analytical results was proven by recovery experiments by method comparison with standard addition methods and measurement of digested wines. In addition to applying statistical methods for characterizing the precision of the methods, the uncertainty of the measurements was estimated.Results for the elements mentioned above and additional 16 elements (Al, B, Ba, Ca, Cr, Cu, Fe, Mn, Mg, P, Pb, Si, Sn, Sr, V, and Zn) were evaluated by data analytical methods. Due to a specific choice of the analytes for multivariate statistical investigation a prediction rate by cross validation of 88.6% could be achieved.
Transformations of metal species in ageing humic hydrocolloids studied by competitive ligand and metal exchange by Peter Burba; Johan Van den Bergh (pp. 1637-1643).
Transformations of metal species (particularly Al, Ca, Fe, Mg, Mn, Zn) in ageing humic hydrocolloids were studied, applying a competitive ligand and metal exchange approach. For this purpose, metal-containing hydrocolloids, freshly collected from humic-rich German bog lake waters (Hohlohsee (HO), Black Forest; Venner Moor (VM), Muensterland; Arnsberger Wald (AW), Northrhine-Westfalia) and conventionally pre-filtered through 0.45 μm membranes, were subjected on-site to an exchange with EDTA and Cu(II) ions, respectively, as a function of time. EDTA complexes gradually formed, metal fractions exchanged by Cu(II) (as well as free Cu(II) concentrations) were operationally discriminated by means of a small time-controlled tangential-flow ultrafiltration unit (nominal cut-off: 1 kDa). Metal and DOM (dissolved organic matter) fractions obtained this way were determined off-site using instrumental methods (AAS, ICP-OES, carbon analyzer). After weeks of storage, the collected hydrocolloids were studied again by this approach. The EDTA availability of colloid-bound metals (particularly Al and Fe) exhibited different ageing trends, dependent on the sample (VM: decrease of Fe availability (98–76%), HO: increase of Fe availability (76–82%)). In contrast, the Cu(II) exchange equilibria of colloid-bound metals revealed merely low availability of Al (16–38%) and Fe (5–11%) towards Cu(II) ions, also dependent on ageing effects. In particular, the conditional copper exchange constants K ex obtained from the exchange between Cu(II) ions and available metal species (such as Ca, Mg, Mn, Zn) exhibited a strong decrease (by a factor of 2–100) during sample storage, indicating considerable non-equilibria complexation of these metal ions in the original bogwaters studied on-site.
Keywords: Hydrocolloids; Metal species; Transformation; EDTA availability; Cu(II) exchange
Highly-sensitive simultaneous detection of lanthanide(III) ions as kinetically stable aromatic polyaminocarboxylato complexes via capillary electrophoresis using resolution enhancement with carbonate ion by Shingo Saito; Hitoshi Hoshino (pp. 1644-1647).
An aromatic polyaminocarboxylate ligand, 1-(4-aminobenzyl)ethylenediamine-N,N,N′,N′-tetraacetate (ABEDTA), is proposed as a complexing reagent in the pre-capillary mode so as to form kinetically inert Ln(III) complexes, meaning that no added ligand is necessary in alkaline carrier buffer solutions. In addition, highly-sensitive detection is possible through a light-absorbing moiety of an aminobenzyl group in the ligand. The fine-tuning of the electrophoretic mobilities of the Ln-abedta complexes is successfully achieved by adding an auxiliary carbonate ion ligand which alters the charge-to-size ratio of the complexes through fast exchange equilibria in a carrier buffer. In fact, all of the complexes are detectable with very similar analytical sensitivity and acceptable resolution (except for Ln=Sm, Eu, Gd) by using NaOH-borate carrier buffer solution at pH 12.35 with 20 mM of Na2CO3. A typical detection limit for Tb(III) ion (to 3σ) is as low as 0.94 μM, which translates to an absolute amount of 9.4 fmol in a 1.0×10−8 dm-3 (10 nL) injection.
Keywords: Capillary electrophoresis; Lanthanide ions; Polyaminocarboxylate; Inert complex; Ternary complex
Synchronous fluorescence for simultaneous determination of hydroquinone and resorcinol in air samples by M. Pistonesi; M. E. Centurión; M. Pereyra; A. G. Lista; B. S. Fernández Band (pp. 1648-1651).
Several phenolic compounds are present in tobacco smoke. They are formed from the pyrolysis of tobacco during the smoking process and all of them are toxic. Therefore, the determination of these compounds in air samples is important. A rapid, simple, and sensitive method using a synchronous spectrofluorimetry technique was developed to quantify hydroquinone and resorcinol simultaneously. One of the advantages of this method is the simple and rapid sampling technique, which uses water as the absorption solution of the analytes in the air sample. The precision of the method (%RSD) was 1.8% and the detection limits were 0.125 mg m−3 and 0.292 mg m−3 for hydroquinone and resorcinol, respectively.
Keywords: Synchronous fluorescence; Phenolic compounds; Air
Fluorimetric determination of aluminium in water by sequential injection through column extraction by C. Brach-Papa; B. Coulomb; C. Branger; A. Margaillan; F. Théraulaz; P. Van Loot; J.-L. Boudenne (pp. 1652-1658).
A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al3+ at the sub-ppb level (LOD: 0.2 μg L−1 for 1 ml of sample) within a working range of 0.2–500 μg L−1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.
Keywords: Aluminium; Solid phase extraction; Chelating resin; Fluorimetry; Drinking water
A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques by M. Mazloum Ardakani; M. Salavati-Niasari; M. Khayat Kashani; S. M. Ghoreishi (pp. 1659-1665).
A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10−5–1.0×10−1 M and 6.0×10−6–1.0×10−1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10−6 and 6.0×10−6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu2+ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu2+ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.
Keywords: Sol-gel; Thiosemicarbazone; Ion-selective electrodes; Coated-wire electrodes; Copper
Coated wire chromium(III) ion-selective electrode based on azamacrocycles by Aparna Sil; Vijaykumar S. Ijeri; Ashwini K. Srivastava (pp. 1666-1669).
Tetraazacyclotetradecane, tetratosyltetraaza 12C4, and tritosyltriaza 9C3 have been explored as electroactive materials for preparing coated wire ion-selective electrodes (CWISEs) for Cr(III) ions. The best performance was observed for the membrane comprising electroactive material (tetratosyltetraaza 12C4), plasticizer (dibutyl phthalate), and poly(vinyl chloride) in the optimum ratio 5:60:35 (w/w). Linear Nernstian response for this electrode was obtained over the total Cr(III) concentration range of 1×10−1 to 1×10−7 M in 0.05 M NH4NO3 medium, with a slope of 20±1 mV per decade change. The working pH range of the electrode was 1.8–5.5. Selectivity coefficients of some mono, divalent, and trivalent metal ions were determined. Analyses of electroplating bath solutions, chromating, and effluent samples have been carried out using this CWISE and the results are found to be comparable with those obtained by using conventional methods or by AAS.
Keywords: Potentiometry; Coated wire ISE; Chromium(III); Tritosyltriaza 9C3; Tetratosyltetraaza 12C4; Tetraazacyclotetradecane