Orthogonal Wavelets Analysis of Electroanalytical Signals

ABSTRACT

A signal processing technique based on orthogonal wavelet analysis is applied to process various simulated electroanalytical signals. The results indicate that if the scale parameters are selected, the orthogonal wavelet processing method (OWPM) can remove high-frequency noise. Experimental signal was recorded by computer and used to test the OWPM procedure. After processing with OWPM, the processed data was used to analyze the mechanism of the electrode reactions. Processed results of the experimental data are also satisfactory.     

Characterization of chemically bonded phases on precoated thin-layer plates by29Si and13C cross-polarization and magig-angle spinning NMR

Summary The paper reports results for commercial precoated plates and home-made bonded phases for TLC examined by²⁹Si and¹³C NMR of solid samples. The NMR spectra readily reveal differences in degree of silylation, details pertaining to the type of reactive silanes used, and differences in the methods of synthesis. They can also be used to explain the cause of the wettability problems encountered with some types of (precoated) TLC plates.     

ResonSense: simple linear fluorescent probes for quantitative homogeneous rapid polymerase chain reaction

Here we report a strand-specific fluorescent homogeneous assay format for rapid polymerase chain reaction (PCR). A number of similar assays are commonly used for research applications and are an ideal solution for a closed tube quantitative PCR. These assays use fluorescent resonant energy transfer (FRET) between donor and acceptor fluorescent moieties as the reporting mechanism. However, for different reasons these assays do not report amplification when very rapid cycling times are used. This is because current assays, such as TaqMan^®, are limited, in terms of assay speed, by the 5′-3′ exonuclease activity of Taq DNA polymerase. Other assays based on hybridisation require either a complex de-conformational event to occur, or require more than one probe to report amplification. Reducing the complexity of the experiment reduces costs in terms of design, optimisation and manufacture. Here, we describe ResonSense^® chemistries that use a simple linear fluorescent-labelled probe and a DNA minor-groove binding dye as either donor or acceptor moieties in a homogeneous assay format on the LightCycler^®. This assay format will provide for rapid analysis of samples and so it is particularly well suited to point-of-use testing.     

Application of artificial neural network to simultaneous potentiometric determination of silver(I), mercury(II) and copper(II) ions by an unmodified carbon paste electrode

The response characteristics and selectivity coefficients of an unmodified carbon paste electrode (CPEs) towards Ag⁺, Cu²⁺ and Hg²⁺ were evaluated. The electrode was used as an indicator electrode for the simultaneous determination of the three metal ions in their mixtures via potentiometric titration with a standard thiocyanate solution. A three-layered feed-forward artificial neural network (ANN) trained by back-propagation learning algorithm was used to model the complex non-linear relationship between the concentration of silver, copper and mercury in their different mixtures and the potential of solution at different volumes of the added titrant. The network architecture and parameters were optimized to give low prediction errors. The optimized networks were able to precisely predict the concentrations of the three cations in synthetic mixtures.     

Studies on the P-branch spectral lines of rovibrational transitions of diatomic system

An analytical formula is used to predict the accurate P-branch spectral lines of rovibrational transitions for diatomic systems. The formula is derived from elementary expression of molecular total energy by taking multiple spectral differences. It is not only reproduces the known experimental transition lines by using a group of fifteen known experimental transition data, but also predicts the accurate spectral lines that may not be available experimentally. The P-branch emission spectra of the (0,1), (0,2) and (0,3) bands of the B(2)∑(+)→X(2)∑(+) system in the (12)C(17)O(+) molecular ion are studied, and correct values of the unknown spectral lines up to J=80.5 for each band are predicted using the formula.     

NMR STUDY OF EXCHANGE KINETICS OF THE LITHIUM ION WITH CRYPTAND C222 IN BINARY ACETONITRILE-NITROMETHANE MIXTURES

Abstract

The exchange kinetics of the lithium ion with cryptand C222 were studied in acetonitrile-nitromethane mixtures by lithium-7 NMR line-shape analysis. In all solvent mixtures used, and over the entire temperature range studied, the chemical exchange of the Li⁺ ion between the solvated and complexed sites was found to occur via a bimolecular mechanism. The activation parameters E_a, δH?, δS? and δG? for the exchange have been determined. The free energy barrier for the exchange process appears to be nearly independent of the binary mixture composition. The results confirm the preferential solvation of the lithium ion with acetonitrile in the binary mixed solvent systems used.     

Structure Solution of Nano-Crystalline Small Molecules Using MicroED and Solid-State NMR Dipolar-Based Experiments

Three-dimensional electron diffraction crystallography (microED) can solve structures of sub-micrometer crystals, which are too small for single crystal X-ray crystallography. However, R factors for the microED-based structures are generally high because of dynamic scattering. That means R factor may not be reliable provided that kinetic analysis is used. Consequently, there remains ambiguity to locate hydrogens and to assign nuclei with close atomic numbers, like carbon, nitrogen, and oxygen. Herein, we employed microED and ssNMR dipolar-based experiments together with spin dynamics numerical simulations. The NMR dipolar-based experiments were ¹H-¹⁴N phase-modulated rotational-echo saturation-pulse double-resonance (PM-S-RESPDOR) and ¹H-¹H selective recoupling of proton (SERP) experiments. The former examined the dephasing effect of a specific ¹H resonance under multiple ¹H-¹⁴N dipolar couplings. The latter examined the selective polarization transfer between a ¹H-¹H pair. The structure was solved by microED and then validated by evaluating the agreement between experimental and calculated dipolar-based NMR results. As the measurements were performed on ¹H and ¹⁴N, the method can be employed for natural abundance samples. Furthermore, the whole validation procedure was conducted at 293 K unlike widely used chemical shift calculation at 0 K using the GIPAW method. This combined method was demonstrated on monoclinic l-histidine.     

Gas Chromatographic Determination of Microgram and Nanogram Quantities of Histamine as Its Na-Trifluoroacetyl-Nim-Carbethoxy Derivative

Abstract

A method has been devised for the quantitative estimation of microgram and nanogram quantities of histamine as its N^a-trifluoroacetyl-N^im-carbethoxy derivative. Trifluoroacetic anhydride was used for the formation of N^a-trifluoroacetyl derivative and ethoxyformic anhydride was used for the N^im-carbethoxy derivative. Quantitative determinations were made in the range of 20 to 100 micrograms and 250 and 1000 nanograms with a mean standard deviation of 2–3%. The standard curves were linear.     

Simultaneous mixture analysis by using non-linear spectrophotometric data and linear iterative target transformation factor analysis

Non-linear absorption spectral data obtained from ternary mixtures of analytes are analyzed by using a linear model, iterative target transformation factor analysis (ITTFA). The use of transformed original variables is used to correct non-linearities in the original data. Absorbance below a certain limit (k) is described as linear and above this limit as non-linear. The extension of the regressor variables is the squared absorbances above the linear range. The variation of the prediction error as a function of the number of the factors and the k-values were considered and the minimum prediction error was evaluated for reaching to optimum. Except the natural non-negativity constraint the correlation constraint also is used on concentration vector in each iteration of ITTFA algorithm. The reliability of the method is evaluated using model data for ternary mixtures by spectral overlapping and different degrees of non-linearity. Simultaneous spectrophotometric determination of Eu³⁺, UO₂²⁺ and Th⁴⁺ with arsenazo III as chromogenic reagent is used as experimental model systems with non-linearity behavior of Eu³⁺and UO₂²⁺ components. The application to both synthetic and real data sets with different degrees of non-linearity demonstrate the ability of the proposed methodology to obtain better results than original data and ITTFA. The relative standard errors of prediction for proposed method in comparison with using the PLS calibration on original and extended data are nearly smaller.     

Determination of oil reservoir radiotracer (SCN) in a single step using a plastic scintillator extractive resin

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S¹⁴CN⁻. Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS.     

Standardized basis sets for high-level-correlated relativistic calculations of atomic and molecular electric properties in the spin-averaged Douglas-Kroll (no-pair) approximation I. Groups Ib and IIb

Summary The technique developed earlier for the generation of the so-called first-order polarized basis sets for accurate non-relativistic calculations of molecular electric properties is used to obtain similar basis sets suitable for calculations in the Douglas-Kroll no-pair approximation. The corresponding (relativistic) basis sets are devised for atoms of the Groups Ib and IIb of the periodic table and tested in calculations of atomic polarizabilities and dipole moments of the coinage metal hydrides. Excellent performance of these basis sets has been found in the case of molecular calculations.     

Analytical methods to determine Po and Pb in marine samples

This paper describes the methods of sampling, preconcentration, chemical separation and final count of ²¹⁰Po and ²¹⁰Pb present in different marine matrices to determine their background levels in a marine ecosystem. Complex, time consuming and selective radioanalytical methods have been used to prepare final clear sources for alpha spectrometry and beta count; in fact, gamma spectrometry, a method direct and non destructive, cannot be taken into account because the ²¹⁰Pb activity is very low which does not allow to carry out sufficiently accurate measurements and ²¹⁰Po is not a gamma emitter but it emits only alpha particle at 5.40 MeV. The results of ²¹⁰Po and ²¹⁰Pb activity concentrations obtained in different marine samples collected in the first two campaigns are still very few to discuss about the ²¹⁰Po and ²¹⁰Pb behavior in marine environment.     

The fractionation and determination procedures for the speciation of Pb and Po in soil samples

A method for speciation and determination of ²¹⁰Pb and ²¹⁰Po in soil samples was developed. The speciation was carried out by fractionating the soil samples into five fractions which are water soluble or exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and bound to residue. After mineralisation, 10% solution of each fraction was used to spontaneously deposit polonium on a silver disk at 85-90 °C and pH 1.5, and ²¹⁰Po was measured by α-spectrometry; the remain solution was used to separate lead by anion-exchange resin and purified by precipitation as PbS and PbSO₄, and ²¹⁰Pb was determined by a low background β-counter. The IAEA-327 reference material (soil) was studied for ²¹⁰Pb and ²¹⁰Po speciation. The results show that: (1) the average yields are 88.7 ± 6.4% for ²¹⁰Pb and 93.8 ± 8.2% for ²¹⁰Po; (2) if compared to the total ²¹⁰Pb activity in the sample, ²¹⁰Pb fractions are 0.95% in exchangeable form, 10.6% bound to carbonates, 14.3% bound to Fe-Mn oxides, 7.0% bound to organic matter and 67.2% bound to residue or acid soluble, and the corresponding values for ²¹⁰Po are 0.17%, 0.97%, 21.0%, 0.47% and 77.4%, respectively; and (3) the obtained ²¹⁰Pb concentration is in good agreement with the recommended value given by the IAEA.     

Solvation of Na+ in N,N-dimethylformamide + methanol solutions. A nuclear magnetic relaxation study using dynamic solvent isotope effects

Inter- and intramolecular nuclear magnetic quadrupole relaxation measurements have been used to study the system methanol (CH₃OH)+ N,N-dimethylformamide (DMF)+NaI at 25°C. The dynamic behavior of the solvent molecules was investigated, throughout the composition range of the binary mixtures, by means of ¹⁴ N relaxation of DMF and ² H of methanol-d ₁ (CH ₃ OD). The intermolecular relaxation of ²³ Na⁺ in pure DMF was used to obtain information about the symmetry of the solvent electric dipole arrangement in the solvation sphere of the ion. The investigation of preferential solvation around Na⁺ in the binary mixtures was carried out by means of ²³ Na⁺ relaxation measurements using, for the first time, both the CH ₃ OH/CD ₃ OD and the DMF/DMF-d ₇ dynamic isotope effect. The results show that, throughout the composition range, there is preferential solvation by DMF. Furthermore, the use of the isotope effects of both components allowed for the first time a basic check of the reliability of the method since we obtained two independent sets of data for the composition of the Na⁺ solvation shell in the mixtures. The consistency of the two separate data sets demonstrates that the application of the dynamic isotope effect represents a powerful tool in preferential solvation studies.     

Nuclear magnetic resonance of donor atoms as a tool for determination of the structure of platinum metal complexes in solutions

Data on the NMR spectroscopy of C, N, O, Si, P, and Sn donor atoms of platinum metal complexes in solutions are surveyed. The chemical shift of a donor atom mainly depends on the ligand in the trans-position (due to the trans-effect). The chemical shift of a donor atom on a particular coordinate of the complex (coordinate shift, CSh) is an attribute of this coordinate and can be used to identify such a coordinate in platinum metal complexes and to determine the structures of complexes. Based on the known data, CSh diagrams were composed for ¹H, ¹³C, ¹⁴N, ¹⁷O, ¹⁹F, ³¹P, and ¹¹⁹Sn. Examples of using the CShs for determining the structures of platinum metal complexes in solutions are presented.     

Recombination of KrD and XeD ions with electrons

Recombination rate coefficients of protonated and deuterated ions KrH⁺, KrD⁺, XeH⁺ and XeD⁺ were measured using Flowing Afterglow with Langmuir Probe (FALP). Helium at 1600 Pa and at temperature 250 K was used as a buffer gas in the experiments. Kr, Xe, H₂ and D₂ were introduced to a flow tube to form the desired ions. Because of small differences in proton affinities of Kr, D₂ and H₂ mixtures of ions, KrD⁺/D₃⁺ and KrH⁺/H₃⁺ are formed in the afterglow plasma, influencing the plasma decay. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The obtained rate coefficients, α_KrD+(250 K) = (0.9 ± 0.3) × 10⁻⁸ cm³ s⁻¹ and α_XeD+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹ are compared with α_KrH+(250 K) = (2.0 ± 0.6) × 10⁻⁸ cm³ s⁻¹ and α_XeH+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹.     

31P NMR and HPLC Investigations of the Cyclophosphamide Metabolite,Phosphoramide Mustard

Abstract

Phosphoramide mustard (PM), a key active metabolite of the widely used anticancer drug cyclophosphamide (CP), can exist in several closely-related ionized, cyclized and substituted forms. We have developed a high pressure liquid chromatographic (HPLC) method for analysing serum concentrations of PM in order to relate these serum concentrations to toxicity and efficacy of treatment of CP. ³¹p NMR spectroscopy is used to verify the HPLC peak homology of the proposed PM peak.     

Characterization and application of humic acid modified carbon electrodes

Four routes for the modification of carbon electrodes with humic acids and the determination of three divalent metallic cations were studied. The determination of bound Fe²⁺, Cu²⁺ and Ni²⁺ was performed by cyclic and square wave voltammetry using either a batch or flow analysis system. Using the FIA system and SWV, linear relationships between the oxidation (or reduction) current and the cations concentration were obtained with the modified electrodes, while no signals were obtained for the same conditions for bare carbon electrodes. The system can be used to study the interaction between a wide range of electroactive cations and humic substances; however, the performance as an analytical tool is limited due to the high limits of detection (μM). However, some advantages like simplicity, short analysis time, inexpensive instrumentation needs and miniaturization capabilities are remarkable.     

Development of an optical membrane for humidity

4-(N,N-dioctylamino)-4-trifluoroacetyl-azobenzene (ETH^T 4001), together with the catalyst tridodecylmethylammonium chloride, is dissolved in the hydrophilic polymer polyurethane Tecoflex. The resulting membrane layers show high sensitivity toward water vapour and allow the application of the membranes for humidity measurements. Upon exposure to humid air, the membrane exhibits a decrease in absorbance at a wavelength around 490 nm and an increase at around 430 nm. This signal change is caused by the conversion of the trifluoroacetyl group of the reactand into a diol, thus changing the electron delocalisation of the reactand. The sensor layer exhibits a dynamic range from 1% to 100% RH with highest sensitivity in the 5%–40% RH range. The limit of detection is 0.5% RH. The amount of added catalyst enables the sensitive range to be tailored. The selectivity over ethanol and carbonate is sufficient for the membrane to be used for long-term measurements of air. The change in colour of the humidity-sensitive membrane from red to yellow also means it can be used as an optical test strip.     

A Proton NMR Study of the Stoichiometry and Stability of 18-Crown-6 Complexes with K+, Rb+ and Tl+ Ions in Binary Dimethyl Sulfoxide-Nitrobenzene Mixtures

Proton NMR spectroscopy was used to study the complexation reaction of 18-crown-6 (18C6) with K⁺, Rb⁺ and Tl⁺ ions in a number of binary dimethyl sulfoxide-nitrobenzene mixtures. In all cases, the exchange between free and complexed crowns was fast on the NMR time scale and only a single population average ¹H signal was observed. Formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. There is an inverse relationship between the complex stability and the amount of dimethyl sulfoxide in the mixed solvent. It was found that, in all solvent mixtures used, Rb⁺ ion forms the most stable complex with 18-crown-6 in the series.