Multi-layered analyses using directed partitioning to identify and discriminate between biogenic amines

Multiple layers of statistical analyses were used to decipher the response from a single, cross-reactive conjugated polymer (1) providing enhanced classification accuracies over traditional multivariate statistical approaches. This analysis was demonstrated by classifying a series of seven biologically relevant, nonvolatile amines (i.e. biogenic amines). If only a single layer of analysis was employed (linear discriminant analysis), 89% classification accuracy was achieved lacking any concentration information. However, using this multi-layered, group-ungroup method, the analytes were first categorized based on general class of molecule (directed partitioning), i.e. aromatic, aliphatic, polyamines, with 98% accuracy. In a second analysis layer, these sub-groups were broken down into the individual molecular components, with the aliphatic and aromatic amines classifying near 99%, while the polyamine identification accuracy approached 90%. In the third layer of analysis, the concentration of the analytes in question was determined in the biologically relevant range within approximately 10% accuracy by following trends in the principle component analysis output.     

Tracking human travel using stable oxygen and hydrogen isotope analyses of hair and urine

The stable oxygen and hydrogen isotope compositions of organic samples are increasingly being used to investigate patterns of animal migration. Relatively few studies have applied these techniques to modern humans, despite a variety of potential forensic applications. We analyzed drinking water and food at two geographic locations, East Greenbush, New York (USA) and Fairbanks, Alaska (USA), with different delta(18)O and deltaD values for precipitation and tap water. Foods varied widely in measured delta(18)O and deltaD values, but not systematically by purchase location. We measured delta(18)O and deltaD values of scalp hair from five residents at each location. We used a mixing model to establish the proportion of oxygen and hydrogen in head hair derived from drinking water ( approximately 27% and approximately 36%, respectively). Finally, we analyzed the delta(18)O and deltaD values of facial hair and urine from a subject who traveled from Fairbanks to East Greenbush, on to the UK and back to Fairbanks. Urine delta(18)O and deltaD values responded immediately and strongly to travel-related change in drinking water, and were well described by a single-pool turnover model. Beard hair delta(18)O values tracked changes in urine delta(18)O closely, and oscillated between the values for the resident populations in both locations. In contrast, beard hair deltaD values did not track changes in urine deltaD as well, and retained a signature of the traveler's permanent residence. Our findings show that the delta(18)O and deltaD values of urine and facial hair (specifically delta(18)O) can provide a record of the geographical movements of humans.     

Uranium and thorium analyses by delayed fission neutron counting technique using a small neutron generator

Applicability of a small neutron generator and a dual rectangular tube sample transfer system for analyses of U and Th using delayed fission neutron technique has been investigated. A way of optimizing the timing parameters is reported. At a fast neutron flux of 10⁸ n.cm^–2s^–1, 0.02 w% U can be determined. For thorium determination this method is less sensitive. The Cd difference technique can be used for the simultaneous determination of U and Th but it has lower sensitivity.This work was supported in part by the IAEA.     

In situ investigation of dye adsorption on TiO2 films using a quartz crystal microbalance with a dissipation technique

Dye adsorption plays a crucial role in dye-sensitized solar cells. Herein, we demonstrate an in situ liquid-phase analytical technique to quantify in real time adsorption of dye and coadsorbates on flat and mesoporous TiO(2) films. For the first time, a molar ratio of co-adsorbed Y123 and chenodeoxycholic acid has been measured.     

Thermal degradation characteristics of a novel flame retardant coating using TG-IR technique

A novel phosphate acrylate monomer (TGMAP) has been synthesized by allowing phosphoric acid to react with glycidyl methacrylate. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The char yield was 36.3% at 600 °C. TG data indicate that the material undergoes degradation in three characteristic temperature stages, which can be attributed to the decomposition of the phosphate, thermal pyrolysis of aliphatic chains, and degradation of an unstable structure in char, respectively. The volatilized products formed on thermal degradation of TGMAP indicated that the volatilized products are CO, CO₂, carboxylic acid, acid anhydride, water, alkane, and aromatic compounds according to the temperature of onset formation.     

The isotope exchange depth profiling (IEDP) technique using SIMS and LEIS

The determination of the mass transport kinetics of oxide materials for use in electrochemical systems such as fuel cells, sensors and oxygen separators is a significant challenge. Several techniques have been proposed to derive these data experimentally with only the oxygen isotope exchange depth profile technique coupled with secondary ion mass spectrometry (SIMS) providing a direct measure of these kinetic parameters. Whilst this allows kinetic information to be obtained, there is a lack of knowledge of the surface chemistry of these complex processes. The advent of low-energy ion scattering (LEIS) now offers the opportunity of correlating exchange kinetics with chemical processes at materials atomic surfaces, giving unprecedented levels of information on electrochemical systems with isotopic discrimination. Here, the challenges of these techniques, including sample preparation, are discussed and the advantages of the combined approach of SIMS and LEIS illustrated with reference to key literature data.     

Oxygen evolution on Ru and RuO2 electrodes studied using isotope labelling and on-line mass spectrometry

Oxide layer formation and O₂ evolution on Ru and RuO₂ films have been studied in sulphuric acid using ¹⁸O labelling together with differential electrochemical mass spectrometry (DEMS). It was shown that ¹⁶O¹⁸O is evolved from a H₂¹⁶O solution on a Ru oxide layer previously formed in H₂¹⁸O. ¹⁶O¹⁸O was also observed when oxygen is evolved on Ru¹⁶O₂ in H₂¹⁸O solution. Consequently, the oxide layer takes part in the oxygen evolution process on both types of electrode. In the case of Ru, formation of RuO₄ was observed when oxygen evolution takes place.     

Separation and determination of biogenic amines in fish using MEKC with novel multiphoton excitation fluorescence detection

Biogenic amines are a group of biological molecules derived from the enzymatic decarboxylation of natural amino acids. They can be found in a variety of foods and some of them are involved in essential cellular pathways regulating cellular functions. To address the issues raised by conventional detection methods for biogenic amines, such as laborious sample preparation and limited sensitivity, a new micellar electrokinetic chromatography scheme was developed based on multiphoton excitation fluorescence (MPEF) detection. Six FITC-labeled biogenic amine species were used for the evaluation of this MEKC-MPEF method in comparison to single photon excitation fluorescence detection. The results indicated that MEKC-MPEF had superior resolution with a detection volume as low as aL. Quantitative analysis of varying concentrations of biogenic amine species has also been achieved suggesting a ymole mass detection limit, a linear dynamic range of about two orders of magnitude, and 95-105% recoveries. Furthermore, the biogenic amine profile of decayed oriental crucian carps was successfully determined and quantified using this new method.     

Lectin-carbohydrate affinity measured using a quartz crystal microbalance

The association of two molecules is described by two parameters, association equilibrium and association rate constants, which are characteristic for a given type of interaction. Usually, they are determined for interacting molecules dissolved in solution. However, for many applications one type of molecules is immobilized on a substrate, which may influence the binding kinetics. The studied complex of concanavalin A and carboxypeptidase Y belongs to the lectin-carbohydrate type of interaction involving the recognition of oligosaccharide moieties. The concanavalin A was immobilized on a gold electrode of quartz crystal, while carboxypeptidase Y was added to a buffer (Tris-buffered saline). The constants describing the association of the investigated molecules were determined on the basis of measurements performed using a quartz crystal microbalance in liquid. The obtained values were (0.59+/-0.01)x10(6) M(-1) for the association equilibrium constant and (5.6+/-0.1)x10(4) M(-1)s(-1) for the association rate constant. The saturation binding experiment gave another value of the association constant, (2.7+/-0.02)x10(6) M(-1). The comparison of obtained values with previously published ones verifies that the molecule orientation and binding site accessibility for specific ligands could influence the association equilibrium constant value. The presented measurements demonstrate the ability of a quartz crystal microbalance to detect and to evaluate the association process occurring between molecules.     

Oxygen isotope exchange in oxygen-bearing compounds of uranium

Isotope exchange is reported for gaseous oxygen in contact with the following uranium compounds: -Na₂UO₄, -Na₂UO₄, Na₂U₂O₇, UO₃(A), -UO₃, -UO_2.94 and U₃O₈.; qualitative tests have also been done with UO₂F₂ and Cs₂UO₂Cl₄. The times of half-exchange have been determined as functions of temperature for U₃O₈, -UO_2.94, Na₂U₂O₇ and -Na₂UO₄; diffusion coefficients for oxygen have been calculated for UO₃(A), -UO₃, Na₂U₂O₇, -Na₂UO₄ and -Na₂UO₄. Activation energies have been deduced for diffusion and surface exchange. All the oxygen atoms in these compounds are equivalent as regards isotope exchange; the above activation energies increase with the UO ratio in some cases. Diffusion-limited exchange tends to show periodic oscillations in rate not ascribable to errors of measurement; a mechanism is proposed for this.     

Stable isotope dilution analyses of molybdenum in meteorites

Isotope dilution mass spectrometry is an ideal analytical technique to measure the elemental abundance of Mo in C1 carbonaceous chondrites and the metallic and troilite phases of iron meteorites. The mean abundance of Mo in two C1 meteorites is 0.909 ± 0.040 μg/g which corresponds to a value of 2.55 atoms Mo with respect to Si equal to 10⁶ atoms, which is identical to the currently accepted solar system abundance. The partitioning of Mo between the metallic and sulfide phases in the Mundrabilla iron meteorite was found to be 6.0 ± 0.2 μg/g and 8.6 ± 0.3 μg/g, respectively. A new, precise Mo concentration of 1.54 ± 0.04 μg/g for the Geochemical Reference Standard BCR-1 is also reported. Received: 15 December 1999 / Revised: 13 March 2000 / Accepted: 16 March 2000     

Stable isotope dilution analyses of molybdenum in meteorites

Isotope dilution mass spectrometry is an ideal analytical technique to measure the elemental abundance of Mo in C1 carbonaceous chondrites and the metallic and troilite phases of iron meteorites. The mean abundance of Mo in two C1 meteorites is 0.909+/-0.040 microg/g which corresponds to a value of 2.55 atoms Mo with respect to Si equal to 10(6) atoms, which is identical to the currently accepted solar system abundance. The partitioning of Mo between the metallic and sulfide phases in the Mundrabilla iron meteorite was found to be 6.0+/-0.2 microg/g and 8.6+/-0.3 microg/g, respectively. A new, precise Mo concentration of 1.54+/-0.04 microg/g for the Geochemical Reference Standard BCR-1 is also reported.     

Visualization of large-scale aqueous solubility data using a novel hierarchical data visualization technique

It is a difficult task to recognize the trends in molecular physical properties relevant to a specific chemical class and find a way to optimize potential compounds. We present here a novel hierarchical data visualization technique, named "HeiankyoView", to visualize large-scale multidimensional chemical information. HeiankyoView represents hierarchically organized data objects by mapping leaf nodes as colored square icons and nonleaf nodes as rectangular borders. In this way, data objects can be expressed as equishaped icons without overlapping one another in the two-dimensional display space. HeiankyoView has been applied to visualize aqueous solubility data for 908 compounds collected from the published literature. When the results of a recursive partitioning analysis and hierarchical clustering analysis were visualized, the trends hidden in the solubility data could be effectively displayed as intuitively understandable visual images. Most interestingly, the data visualization technique, without any statistical computations, was able to assist us in extracting from such large-scale data meaningful information establishing that ClogP and the molecular weight are critical factors in determining aqueous solubility. Thus, HeiankyoView is a powerful tool to help us understand structure-activity relationships intuitively from a large-scale data set.     

The quantification of potassium using a quartz crystal microbalance

N,N'-dibenzyl-4,13-diaza-18-crown-6 (A) and bis[(benzo-15-crown-5)-4'-ylmethyl] pimelate (B) were tested as coatings for two piezoelectric crystals for potassium quantification. Both sensors showed stability, reversibility and sensitivity characteristics that allowed their use in quantitative analysis. However, compound A is much more sensitive to potassium than B. Compound A also shows a larger relative sensitivity for potassium with regard to sodium than B. A pharmaceutical sample of known composition was analysed both by an acoustic wave sensor with a crystal coated with compound A and by conductivity. No statistically significant difference in the median of the results was found (alpha = 0.05), although precision is superior for the conductivity methodology. Performance of the sensor in terms of frequency stability and selectivity was improved by the incorporation of PVC, a plasticizer and a lipophilic salt in the coating composition. Limits of detection found for potassium were 1.92 ppm, or 1.75 ppm for a crystal with a frequency decrease due to coating of 2.9 kHz or 3.9 kHz, respectively. Selectivity coefficients (fixed interference 80 ppm) for potassium over Na, Ca, Al, Zn, Mg, and Fe ranged from 0.103 to 0.332.     

Measurements of sulfur in oil using a pressurised wet digestion technique in open vessels and isotope dilution mass spectrometry

Graz University of Technology has developed a new technique for digesting samples using the well-established high-pressure asher (HPA) from Anton Paar GmbH (Graz, Austria). The digestion is performed in semi-open vessels inside a pressurised autoclave. The new HPA equipment consists of a liner for the autoclave, special sample racks and 30-mL digestion vessels made of quartz, covered with PTFE stoppers. The Laboratory for Isotope Dilution and Nuclear Analysis of the Federal Institute for Materials Research and Testing (BAM, Berlin) tested this new equipment in order to assess its usability for the decomposition of larger sample amounts of gas oils for the measurement of sulfur. Several experiments were carried out using the new sample decomposition technique. In order to test the recovery of the new digestion method, a gas oil material with known sulfur content was chosen, quantified by the validated conventional closed vessel HPA digestion in combination with thermal ionisation mass spectrometry. Isotope dilution mass spectrometry has been applied as analytical method in this investigation. The gas oil was spiked with an isotopic spike material, which is enriched in ³⁴S, and was then wet digested in the HPA. The oxidized sulfur of the dried samples was reduced to H₂S and precipitated as As₂S₃. The sulfur was measured as arsenic monosulfide (AsS⁺). The mass content of sulfur in the gas oil tested is 453.5 mg kg^–1. Recovery tests for increasing masses of gas oils indicate that the recovery using the new measurement technique decreases with increasing mass of gas oil. Results were obtained for approximately 0.3 g sample weight and had less overlap with the result of the old HPA method within the stated uncertainties. At approximately 0.5 g sample weight the yield decreases to about 97% and at approximately 1.0 g sample weight to about 87%. In comparison with the conventional closed vessel HPA digestion, the new technique shows no clear advantages for the certification of the sulfur content in gas oil other than a more convenient handling. The total uncertainty of the sulfur mass fractions (k=2) is about 1.5%. Repeated determination of the oil samples show a relative standard deviation of about 0.8% and indicate that the analytical procedure is robust and reproducible. The demonstrated reproducibility allows the establishment of correction factors for the yield, which in turn enables higher sample masses for routine work. The blank level (0.26×10^-6 g) was within the range of the conventional closed HPA digestion procedure·(0.28×10^-6 g). Cross contamination could not be detected. In terms of trace metal analysis a good applicability and more advantages over the conventional closed vessel HPA digestion can be assumed.     

A novel nanoaggregation detection technique of TNT using selective and ultrasensitive nanocurcumin as a probe

Here, for the first time, we designed an ultrasensitive nanocurcumin based nanomaterials surface energy transfer (NSET) probe for detection of trace amount of TNT with excellent sensitivity (1 nM) and selectivity over other nitro explosives via nanoaggregation and we found the largest fluorescent enhancement to date for sensing TNT (upto 800 fold).     

A novel approach for the homogenization of cellulose to use micro‐amounts for stable isotope analyses

Climate reconstructions using stable isotopes from tree‐rings are steadily increasing. The investigations concentrate mostly on cellulose due to its high stability. In recent years the available amount of cellulose has steadily decreased, mainly because micro‐structures of plant material have had to be analyzed. Today, the amounts of cellulose being studied are frequently in the milligram and often in the microgram range. Consequently, homogeneity problems with regard to the stable isotopes of carbon and oxygen from cellulose have occurred and these have called for new methods in the preparation of cellulose for reliable isotope analyses. Three different methods were tested for preparing isotopically homogenous cellulose, namely mechanical grinding, freezing by liquid nitrogen with subsequent milling and ultrasonic breaking of cellulose fibres. The best precision of isotope data was achieved by freeze‐milling and ultrasonic breaking. However, equipment for freeze‐milling is expensive and the procedure is labour‐intensive. Mechanical grinding resulted in a rather high loss of material and it is also labour‐intensive. The use of ultrasound for breaking cellulose fibres proved to be the best method in terms of rapidity of sample throughput, avoidance of sample loss, precision of isotope results, ease of handling, and cost. Copyright © 2009 John Wiley & Sons, Ltd.