Comparison of algorithms and databases for matching unknown mass spectra

The most used algorithms for the identification of electron-ionization mass spectra are INCOS and probability based matching (PBM). For unknown spectra of high purity, ～75% of rank 1 answers are correct for both algorithms, matched against the National Institute of Standards and Technology 62,235 spectrum database. With matching criteria that retrieve 50% of the possible correct answers from the Wiley 228,998 spectrum database, 54% of the PBM and 42% of the INCOS answers are correct; for 85% purity unknowns, 48% and 27% are correct. For an unknown spectrum of two compounds, neither was reported in the first three INCOS answers; eight of the first ten PBM answers identify both components.     

Comparison of phoswich and ARSA-type detectors for radioxenon measurements

The monitoring of atmospheric radioxenon to ensure compliance with the Comprehensive Nuclear Test Ban Treaty (CTBT) has driven the development of improved detectors for measuring xenon, including the development of a phoswich detector. This detector uses only one PMT to detect β–γ coincidence, thus greatly reducing the bulk and electronics of the detector in comparison to the ARSA-type detector. In this experiment, ¹³⁵Xe was produced through neutron activation and a phoswich detector was used to attain spectra from the gas. These results were compared to similar results from an ARSA-type β–γ coincidence spectrum. The spectral characteristics and resolution were compared for the coincidence and beta spectra. Using these metrics, the overall performance of the phoswich detector for β–γ coincidence of radioxenon was evaluated.     

Database driven analysis for nuclide quantification by gamma spectra

For a set of a priori given radionuclides, extracted from a general nuclide data library, the authors use median estimates of the gamma-peak areas and estimates of their errors to produce a list of possible radionuclides matching gamma-ray line(s) and some measure of the reliability of this assignment.

An a priori determined list of nuclides is obtained by searching for a match with the energy information of the database. This procedure is performed in an interactive graphic mode by markers that superimpose the energy information provided by a general gamma-ray data library on the spectral data. This library of experimental data includes approximately 17,000 gamma-energy lines related to 756 known gamma emitter radionuclides listed by ICRP.     

Comparison of linear and 2D IR spectra in the presence of fast exchange

The few picosecond time scale H-bond making and breaking in the system acetonitrile-methanol dominates the mechanism of vibrational coherence transfer that is evident in the shapes of both the linear and nonlinear IR spectra of the CN group.     

Computer program for processing gamma spectra in neutron activation analysis

A program based on the method of least squares and written in the ALGOL-60 code was developed for data processing in the activation analysis of biological substances. The applicability of the program was checked on synthetic mixtures of the radioisotopes⁶⁴Cu,^69mZn and⁵⁶Mn measured with a scintillation γ-spectrometer.     

A new gamma spectral analysis algorithm for the determination

The aim of the investigation was to determine whether the ¹³⁷Cs contamination found in plants around the Paks Nuclear Power Plant in Paks, Hungary was a result of local emission or of the earlier Chernobyl accident. We distinguished between the two possibilities on the basis of the ¹³⁴Cs/¹³⁷Cs ratio. The ¹³⁴Cs activities to be measured were extremely low, in some cases undetectable with conventional evaluation softwares. Therefore a special algorithm was used to determine the ¹³⁴Cs/¹³⁷Cs ratio. On the basis of the results it is evident, that the contamination originated from Chernobyl.     

Quantitative analysis of X-ray absorption spectra using a 2D map representation

A promising possibility for the quantitative analysis of X-ray absorption near edge structure (XANES) spectra of nanosized electrode materials is demonstrated. We used a 2D map representation technique, which utilizes the values of the first derivatives of the absorbance with respect to the inserted Li(+) content plotted over the two-dimensional space defined by the inserted Li(+) content (mole) versus photon energy (eV) as a single map. The technique was applied to XANES spectra of the Li(y)CoO system in the first Li(+) insertion reaction for determining the structural and electronic variations associated with the change in Li(+) content. The obtained show that the intensities of two peaks at 7725 and 7711 eV increased with the Li(+) content and the difference of intensity change of these two peaks carried out for successive couples of spectra yielded the largest changes at 1.05 and 1.98 mol of Li content. This approach for quantitative analysis of XANES without using conventional simulation techniques enable us to interpret X-ray absorption spectroscopy (XAS) as a quantitative analytical technique with greater confidence.     

Two-dimensional infrared (2D IR) spectroscopy. A new tool for interpreting infrared spectra

Two-dimensional infrared (2D IR) spectroscopy is used to study atactic polystyrene. 2D IR is a technique based on time-resolved detection of IR signals in response to an external perturbation, such as mechanical strain. Since different chemical functional groups respond to the applied perturbation at unique and often different rates, characteristic time-dependent variations of the IR-band intensities are observed. Correlation analysis of the dynamic variation of the IR signals yields a new spectrum defined by two independent wave numbers. Peaks located on a 2D IR spectral plane imply interactions and connectivities among chemical functional groups. By spreading convoluted IR bands over two dimensions, the spectral resolution is also greatly enhanced.     

Computer simulaion of gamma spectra in 14 MeV neutron activation analysis

The method of simulation of gamma-spectra based on the experimental library spectra of particular radioisotopes is described. The library spectra were obtained by activation of pure element sample with the use of a 14 MeV neutron generator, counting them with a NaI(T1) scintillation spectrometer and decomposing of mixed spectra to spectra of separate radioisotopes. The simulated and measured spectra of an artificial sample are compared.     

Advanced solvent signal suppression for the acquisition of 1D and 2D NMR spectra of Scotch Whisky

A simple and robust solvent suppression technique that enables acquisition of high‐quality 1D ¹H nuclear magnetic resonance (NMR) spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky. The method uses 3 channels to suppress signals of water and ethanol, including those of ¹³C satellites of ethanol. It is executed in automation allowing high throughput investigations of alcoholic beverages. On the basis of the well‐established 1D nuclear Overhauser spectroscopy (NOESY) solvent suppression technique, this method suppresses the solvent at the beginning of the pulse sequence, producing pure phase signals minimally affected by the relaxation. The developed solvent suppression procedure was integrated into several homocorrelated and heterocorrelated 2D NMR experiments, including 2D correlation spectroscopy (COSY), 2D total correlation spectroscopy (TOCSY), 2D band‐selective TOCSY, 2D J‐resolved spectroscopy, 2D ¹H, ¹³C heteronuclear single‐quantum correlation spectroscopy (HSQC), 2D ¹H, ¹³C HSQC‐TOCSY, and 2D ¹H, ¹³C heteronuclear multiple‐bond correlation spectroscopy (HMBC). A 1D chemical‐shift‐selective TOCSY experiments was also modified. The wealth of information obtained by these experiments will assist in NMR structure elucidation of Scotch Whisky congeners and generally the composition of alcoholic beverages at the molecular level.     

Stimulated Raman spectra of H2O and D2O

SRS of the valence band of liquid H₂O and D₂O are obtained using a nanosecond pulse from a Q-switched ruby laser. The SRS contours obtained are in overall agreement with those of earlier workers using picosecond pulses and help clarify the results of one of the published works. The broad SRS bands are less likely to be attributed to self-focusing in water, but to the stimulation of overlapping components.     

NMR experiments for the analysis of mixtures: beyond 1D 1H spectra

State-of-the-art technologies and methodologies in NMR spectroscopy make it possible to obtain very informative and high-quality spectra in much less experimental time than classical methods by making better choices of NMR pulse sequences and acquisition parameters. This review presents some recent NMR methods allowing rapid identification, assignment and structural characterization of the components in mixtures. The relative merits of the different NMR pulse sequences are briefly discussed and recommendations are made for the preferred choice of sequences to obtain rapidly artifact-free data. This review covers diffusion experiments (DOSY), HSQC and HMBC experiments, ultra-resolved 2D spectra exploiting the property of aliasing and NOESY/ROESY experiments. It will be in particular shown that selective 1D NOESY/ROESY sequences can be more informative and reach higher resolution in less experimental time than the corresponding 2D sequences.     

Electronic spectra of nucleic acid bases: Variable electronegativity calculations and an analysis of existing results

Variable electronegativity Pariser–Parr–Pople (VE-PPP ) calculations have been carried out on the bases of nucleic acids and 5-fluorouracil. Directions of polarization for the various electronic transitions in these molecules have been calculated using the wave functions obtained by this and the CNDO/S-CI methods. The calculated excitation energies, oscillator strengths, and directions of polarization have been compared with the PPP results due to Pullman and co-workers and Bailey as well as the experimental ones. It has been found that a comparative study of this type is much more useful for understanding the transitions in the molecules than the individual calculations. The VE-PPP method is found to generally give the best results. The directions of polarization have been used to identify the transitions in the molecules and to compare the excitation energies obtained by different methods. It is shown that the transitions in these molecules do not have the characteristics of those of benzene derivatives. All the observed peaks in the molecules have been explained as π^*→π.     

2D F/F NOESY for the assignment of NMR spectra of fluorochemicals

Two-dimensional (2D) NMR is an invaluable technique for the complete analysis and assignment of chemical structures. Although ¹⁹F/¹⁹F COSY experiments are routinely used for assignments in perfluorochemicals, interpretation can be difficult because four-bond (⁴J_FF) coupling constants are typically 5-10-fold larger than vicinal (³J_FF) coupling constants. Furthermore, the dependence of long range coupling constants on stereochemistry is not always known. Fluorine-fluorine NOESY correlations represent an enhancement in the arsenal of 2D ¹⁹F NMR experiments. The NOESY and COSY spectra of 2,2,3,3,4,4,4-heptafluorobutanol and a telomeric perfluorochemical iodide show that COSY identifies the 1,4-fluorine interactions whereas NOESY identifies the vicinal fluorine atoms. The combined experiments have been used to unambiguously assign all of the fluorines in a mixture of cis- and trans-perfluoro-1,3-dimethylcyclohexane and in a substituted perfluorotetrahydrofuran.     

Application of quantitative artificial neural network analysis to 2D NMR spectra of hydrocarbon mixtures

Understanding relationships between the structure and composition of molecular mixtures and their chemical properties is a main industrial aim. One central field of research is oil chemistry where the key question is how the molecular characteristics of composite hydrocarbon mixtures can be associated with the macroscopic properties of the oil products. Apparently these relationships are complex and often nonlinear and therefore call for advanced spectroscopic techniques. An informative and an increasingly used approach is two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy. In the case of composite hydrocarbons the application of 2D NMR methodologies in a quantitative manner pose many technical difficulties, and, in any case, the resulting spectra contain many overlapping resonances that challenge the analytical work. Here, we present a general methodology, based on quantitative artificial neural network (ANN) analysis, to resolve overlapping information in 2D NMR spectra and to simultaneously assess the relative importance of multiple spectral variables on the sample properties. The results in a set of 2D NMR spectra of oil samples illustrate, first, that use of ANN analysis for quantitative purposes is feasible also in 2D and, second, that this methodology offers an intrinsic opportunity to assess the complex and nonlinear relationships between the molecular composition and sample properties. The presented ANN methodology is not limited to the analysis of NMR spectra but can also be applied in a manner similar to other (multidimensional) spectroscopic data.     

Neutron and beta/gamma radiolysis of water up to supercritical conditions. 1. beta/gamma yields for H(2), H(.) atom, and hydrated electron

Yields for H2, H(.) atom, and hydrated electron production in beta/gamma radiolysis of water have been measured from room temperature up to 400 degrees C on a 250 bar isobar, and also as a function of pressure (density) at 380 and 400 degrees C. Radiolysis was carried out using a beam of 2-3 MeV electrons from a van de Graaff accelerator, and detection was by mass spectrometer analysis of gases sparged from the irradiated water. N2O was used as a specific scavenger for hydrated electrons giving N2 as product. Ethanol-d(6) was used to scavenge H(.) atoms, giving HD as a stable product. It is found that the hydrated electron yield decreases and the H(.) atom yield increases dramatically at lower densities in supercritical water, and the overall escape yield increases. The yield of molecular H2 increases with temperature and does not tend toward zero at low density, indicating that it is formed promptly rather than in spur recombination. A minimum in both the radical and H2 yields is observed around 0.4 kg/dm(3) density in supercritical water.     

A new hybrid double divisor ratio spectra method for the analysis of ternary mixtures

A new spectrophotometric method was developed for the simultaneous determination of ternary mixtures, without prior separation steps. This method is based on convolution of the double divisor ratio spectra, obtained by dividing the absorption spectrum of the ternary mixture by a standard spectrum of two of the three compounds in the mixture, using combined trigonometric Fourier functions. The magnitude of the Fourier function coefficients, at either maximum or minimum points, is related to the concentration of each drug in the mixture. The mathematical explanation of the procedure is illustrated. The method was applied for the assay of a model mixture consisting of isoniazid (ISN), rifampicin (RIF) and pyrazinamide (PYZ) in synthetic mixtures, commercial tablets and human urine samples. The developed method was compared with the double divisor ratio spectra derivative method (DDRD) and derivative ratio spectra-zero-crossing method (DRSZ). Linearity, validation, accuracy, precision, limits of detection, limits of quantitation, and other aspects of analytical validation are included in the text.