Radioxenon production through neutron irradiation of stable xenon gas

The Spectral Deconvolution Analysis Tool (SDAT) software was developed to improve counting statistics and detection limits for nuclear explosion radionuclide measurements. SDAT utilizes spectral deconvolution spectroscopy techniques and can analyze both β–γ coincidence spectra for radioxenon isotopes and high-resolution HPGe spectra from aerosol monitors. The deconvolution algorithm of the SDAT requires a library of β–γ coincidence spectra of individual radioxenon isotopes to determine isotopic ratios in a sample. In order to get experimentally produced spectra of the individual isotopes, we have irradiated enriched samples of ¹³⁰Xe, ¹³²Xe, and ¹³⁴Xe gas with a neutron beam from the TRIGA reactor at The University of Texas. The samples were counted in an Automated Radioxenon Sampler/Analyzer (ARSA) style β–γ coincidence detector. The spectra produced show that this method of radioxenon production yields samples with very high purity of the individual isotopes for ^131mXe and ¹³⁵Xe and a sample with a substantial ^133mXe to ¹³³Xe ratio.     

SDAT: analysis of <Superscript>131m</Superscript>Xe with <Superscript>133</Superscript>Xe interference

The Spectral Deconvolution Analysis Tool (SDAT) software was developed at The University of Texas at Austin. SDAT utilizes a standard spectrum technique for the analysis of β–γ coincidence spectra. Testing was performed on the software to compare the standard spectrum analysis technique with a region of interest (ROI) analysis technique. Experimentally produced standard spectra and sample data were produced at the Nuclear Engineering Teaching Laboratory (NETL) TRIGA reactor. The results of the testing showed that the standard spectrum technique had lower errors than the ROI analysis technique for samples with low counting statistics. In contrast, the ROI analysis technique outperformed the standard spectrum technique in high counting statistics samples. It was also shown that the standard spectrum technique benefitted from a compression of the number of channels within the spectra.     

Loss-free counting in NAA using KAYZERO evaluation software

To account for varying dead time (frequently occurring when the measuring time is comparable with the half lives of the radionuclides in question) the use of Westphal's Loss-Free Counting technique (LFC) is preferable. However, standard gamma-ray spectrum deconvolution programs can not be applied in connection with LFC spectrometers, since this technique strongly influences the counting statistics of measured spectra. As consequence, erroneous results are likely to arise when applying peak search routines or when calculating the standard deviation of fitted peak areas or detection limits. To overcome these shortcomings, an LFC module equipped with Dual LFC Mode option should be used: this accumulates an LFC-corrected spectrum simultaneously with an uncorrected spectrum. The KAYZERO evaluation software has been modified to handle such tandem spectra.     

Computerized separation of chromatographically unresolved peaks

A computerized peak deconvolution software and mass spectra were successfully applied for the deconvolution of overlapped peak cluster in the chromatogram obtained separating the complex mixture of pesticides by retention time locking gas chromatography-mass spectroscopy. The method based on the unique fragment ions in the spectra can be used for deconvolution of peak clusters if mass spectra of overlapped peaks differ. This method allows determining actual retention times of overlapped peaks. Peak areas found by this method however, cannot be used naturally for the quantitative purposes as the abundance of fragment ions used for this deconvolution procedure can dramatically differ. Computer assisted deconvolution of peaks in the peak clusters gives more realistic peak area ratios as at this method it is supposed equal response for all peaks overlapped in a cluster.     

SDAT implementation for the analysis of radioxenon β–γ coincidence spectra

The standard deconvolution analysis tool (SDAT) was developed for analysis of radioxenon β–γ coincidence spectra measured as part of the international monitoring system as defined in the comprehensive nuclear-test-ban treaty. The SDAT software analyzes each β–γ coincidence spectrum by fitting library vectors of each radionuclide of interest: ^131mXe, ^133mXe, ¹³³Xe, and ¹³⁵Xe. Detector background and radon are incorporated as optional components of the sample solution. Results are reported in mBq m^?3. A new graphical user interface has been developed to facilitate ease of use and improve the data visualization. Automated energy versus channel calibration algorithms were developed and implemented based on ¹³⁷Cs β–γ coincidence spectra. Details on the user tool and testing are included.     

Analysis of gamma-ray spectra from an aircraft-mounted array of high-resolution sensors

Gamma-ray spectra have been collected using the Environmental Radionuclide Sensor System.². Twenty aircraft-mounted, high-purity germanium sensors are utilized to collect high-resolution environmental spectra. Since time-over-target is limited for aerial surveys, one must often attempt to glean the maximum quantity of information from low-count spectra. The spectral data are collected in a time-stamped-list-mode, which time tags every gamma-ray. This allows a gamma-ray spectrum to be built without dilution for only the time-over-target. The analysis package utilizes photopeaks from natural background isotopes to autocalibrate and gain shift the individual spectra into a composite spectrum. The analysis software utilizes several unique techniques to robustly analyze low-count spectra. It carefully determines the spectral baseline, finds all the peaks which differ from the baseline by more than 4-standard deviations, uses a binary-search technique to fit Gaussian peaks, and utilizes a large library to identify peaks (including minor and escape peaks). Although in an aerial survey, the source geometry is often unknown or difficult to model, the software attempts to assign consistent source strengths to radionuclides. *** DIRECT SUPPORT *** A00E1009 00008     

A software package using a mesh-grid method for simulating HPGe detector efficiencies

Traditional ways of determining the absolute full-energy peak efficiencies of high-purity germanium (HPGe) detectors are often time consuming, cost prohibitive, or not feasible. A software package, KMESS (Kevin’s Mesh Efficiency Simulator Software), was developed to assist in predicting these efficiencies. It uses a semi-empirical mesh-grid method and works for arbitrary source shapes and counting geometries. The model assumes that any gamma-ray source shape can be treated as a large enough collection of point sources. The code is readily adaptable, has a web-based graphical front-end, and could easily be coupled to a 3D scanner. As will be shown, this software can estimate absolute full-energy peak efficiencies with good accuracy in reasonable computation times. It has applications to the field of gamma-ray spectroscopy because it is a quick and accurate way to assist in performing quantitative analyses using HPGe detectors.     

HREELS signal processing via wavelets

In spectroscopy, the recorded spectra can often be modelled as the noisy convolution product of an instrumental function with the ‘true’ signal to be estimated. Such models have often been used for high‐resolution electron energy‐loss spectroscopy (HREELS). In this article, a new method is suggested to estimate the ‘true’ HREELS signal, i.e. the original electronic diffusion function with ‘true’ peak intensities. Our method relies upon the use of wavelets that, because they exhibit simultaneous time and frequency localization, are well‐suited for signal analysis. Firstly, a wavelet shrinkage algorithm is used to filter the noise. This is achieved by decomposing the noisy signal into an appropriate wavelet basis and then thresholding the wavelet coefficients that contain noise. This algorithm has a particular threshold related to frequency and time. Secondly, the broadening due to the instrumental response is eliminated through a deconvolution process. This step mainly rests on the existing relation between the Lipschitz regularity of the signal and the decay with scale of its wavelet coefficients and on least squares. The efficiency of this technique is highlighted by comparing the results obtained with those provided by other published methods. This work is the second in a series of three papers in this issue. The first one presents background knowledge on the wavelets required to understand the estimation methods. The third paper explores the application of wavelet filtering and deconvolution techniques to x‐ray photoelectron spectroscopy. Copyright © 2004 John Wiley & Sons, Ltd.     

A study of the practical limitations of principal components analysis and the labelling of unresolved HPLC peaks

Summary The method of iterative target transformation factor analysis (ITTFA) used in conjunction with second derivative peak finding has shown to be a practical method for the peak deconvolution and reconstruction of HPLC chromatograms and spectra. The second derivative method of peak finding is acceptable for resolutions above 0.5 for peaks of similar heights. Above 0.5 resolution the labelling gives correct results where the spectra are substantially different and also when reasonably similar. Below this value the peak labelling was still accurate where the spectra were different. Solvent effects on the spectra of the compounds studied are small and do not hinder the peak labelling process. Thus small “local” libraries are feasible. Presented at the 17th International Symposium on Chromatography, September 25–30, 1988. Vienna, Austria.     

A universal algorithm for fast and automated charge state deconvolution of electrospray mass-to-charge ratio spectra

This article describes a new algorithm for charge state determination and deconvolution of electrospray ionization (ESI) mass-to-charge ratio spectra. The algorithm (Zscore) is based on a charge scoring scheme that incorporates all above-threshold members of a family of charge states or isotopic components, and deconvolves both low- and high-resolution mass-to-charge ratio spectra, with or without a peak list (stick plot). A scoring weight factor, log (I/I ₀), in which I is the signal magnitude at a calculated mass-to-charge ratio, and I ₀ is the signal threshold near that mass-to-charge ratio, was used in most cases. For high-resolution mass-to-charge ratio spectra in which all isotopic peaks are resolved, the algorithm can deconvolve overlapped isotopic multiplets of the same or different charge state. Compared to other deconvolution techniques, the algorithm is robust, rapid, and fully automated (i. e., no user input during the deconvolution process). It eliminates artifact peaks without introducing peak distortions. Its performance is demonstrated for experimental ESI Fourier transform ion cyclotron resonance mass-to-charge ratio spectra (both low and high resolution). Charge state deconvolution to yield a “zero-charge” mass spectrum should prove particularly useful for interpreting spectra of complex mixtures, identifying contaminants, noncovalent adducts, fragments (N-terminal, C-terminal, internal), and chemical modifications of electrosprayed biomacromolecules.     

Identification of volatiles from pineapple (Ananas comosus L.) pulp by comprehensive two-dimensional gas chromatography and gas chromatography/mass spectrometry

Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications.     

Signal processing and detection limits for graphite furnace atomic absorption with Zeeman background correction

The signal handling requirements for graphite furnace atomic absorption are much more demanding than those for flame atomic absorption. Graphite furnace signals change rapidly, background levels are higher, and signal interpretation needs are more extensive.We have identified a number of signal generation and processing factors that are important for success in graphite furnace analyses. These include: use of the transverse, a.c. Zeeman technique with the magnet on the analyte for background correction; production of a series of signal integrals at line frequency to accurately represent the shape of the furnace peak; use of interpolation techniques to better correct for rapidly changing background levels; use of integrated peak absorbance (A.s) signals rather than peak height absorbance for quantitative measurements; use of baseline correction to improve the accuracy of integrated peak absorbance signals; and use of graphical techniques to facilitate data interpretation and methods development.Examples are presented that illustrate the contribution of these factors to precision and detection limit performance. It is possible to improve detection limits over those previously reported by choosing appropriate signal handling parameters.     

Adjustment of numerical models for gamma-ray spectra of samples when subtracting spectra of matrix elements in neutron activation analysis

Approaches to adjustment of numerical models for gamma-ray spectra of matrix elements are considered. These approaches are aimed at (1) the elimination of the substrate effect in the preparation of the initial spectra of individual elements, (2) the energy calibration of spectra, (3) the improvement of agreement between model and actually observed spectra using the comparison test for peak amplitudes of matrix elements, and (4) special processing of the spectra obtained after the subtraction of matrix elements in the test samples. The adjustment allows the contribution of matrix elements to be more precisely subtracted from the spectra of the samples under study. Thus, additional analytical lines are obtained for some elements, and detection limits are lowered for the majority of lines produced by the standard method of spectrum processing. This extends the potential of neutron activation analysis in solving scientific and practical problems.     

Identification and evaluation of cycling yeast metabolites in two-dimensional comprehensive gas chromatography-time-of-flight-mass spectrometry data

A yeast metabolome exhibiting oscillatory behavior was analyzed using comprehensive two-dimensional gas chromatography-time-of-flight-mass spectrometry (GC x GC-TOF-MS) and in-house developed data analysis software methodology, referred to as a signal ratio method (S(ratio) method). In this study, 44 identified unique metabolites were found to exhibit cycling, with a depth-of-modulation amplitude greater than three. After the initial locations are found using the S(ratio) software, and identified preliminarily using ChromaTOF software, the refined mass spectra and peak volumes were subsequently obtained using parallel factor analysis (PARAFAC). The peak volumes provided by PARAFAC deconvolution provide a measurement of the cycling depth-of-modulation amplitude that is more accurate than the initial S(ratio) information (which serves as a rapid screening procedure to find the cycling metabolites while excluding peaks that do not cycle). The S(ratio) reported is a rapid method to determine the depth-of-modulation while not constraining the search to specific cycling frequencies. The phase delay of the cycling metabolites ranged widely in relation to the oxygen consumption cycling pattern.     

Resampling and deconvolution of linear time-of-flight records for enhanced protein profiling

We have developed a peak deconvolution strategy that is applicable to the full mass range of a time-of-flight (TOF) spectrum. This strategy involves resampling a spectrum to create a time series that has equal peak widths (in time) across the entire spectrum, and then using the deconvolution filters we have previously described. We use this technique to deconvolve the protein mass spectra for blood serum and cell lysates acquired on three separate TOF instruments. Following deconvolution, we resolve spectral structures consistent with expected events such as multiply charged ions, matrix adducts and post-translational protein modifications. The deconvolution procedure produces a 40% improvement in the resolution and enhanced experimental sensitivity over the full length of the linear TOF record, up to m/z 150 000. This approach is particularly appropriate for automated data analysis and peak detection in dense TOF spectra.     

Heteronuclear 1D and 2D NMR Resonances Detected by Chemical Exchange Saturation Transfer to Water

A method to detect NMR spectra from heteronuclei through the modulation that they impose on a water resonance is exemplified. The approach exploits chemical exchange saturation transfers, which can magnify the signal of labile protons through their influence on a water peak. To impose a heteronuclear modulation on water, an HMQC‐type sequence was combined with the FLEX approach. 1D ¹⁵N NMR spectra of exchanging sites could thus be detected, with about tenfold amplifications over the ¹⁵N modulations afforded by conventionally detected HMQC NMR spectroscopy. Extensions of this approach enable 2D heteronuclear acquisitions on directly bonded ¹H–¹⁵N spin pairs, also with significant signal amplification. Despite the interesting limits of detection that these signal enhancements could open in NMR spectroscopy, these gains are constrained by the rates of solvent exchange of the targeted heteronuclear pairs, as well as by spectrometer instabilities affecting the intense water resonances detected in these experiments.     

Characterization of peak purity by fast multiscan circular dichroism detection

Summary A method has been developed to detect inhomogeneity of apparently homogeneous peaks of very similar analytes. The method utilizes the rapid scan feature of state-of-the-art spectrometers/detectors that allow the recording of up to 30 spectra in a single chromatographic peak. Sensitivity and selectivity are enhanced by chiroptical/optical detection. Thus, identification of “front” and “rear” components of the peak can be carried out. The method is exemplified by mixtures of codeine, hydrocodone and oxycodone as analytes. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

Application potential of gas chromatography high speed time-of-flight mass spectrometry system in analysis of pesticides. Part 1

Analysis of pesticides and polychlorinated biphenyls in food matrices was provided by the method of complete two-dimensional gas chromatography/time-of-flight mass spectrometry. It was shown, that using of technology GC/GC is significantly improves separation of target compounds and decrease the limits of quantification in comparison with the common “one-dimensional” chromatography. Also, the study describes briefly the use of rapid separation for the analysis of trace contamination in food samples. High-speed temperature program, coupled with the possibility of deconvolution of spectra, using the TOF-type detector with the appropriate software, significantly reduces the total time of analysis compared with traditional methods.     

Characterization of 40 kDa poly(ethylene glycol) polymers by proton transfer reaction QTOF mass spectrometry and 1H-NMR spectroscopy

Several electrospray mass spectrometry (ESI-MS) techniques have been described during the past years to enable the characterization work of large poly(ethylene glycol)s (PEGs) and PEGylated proteins. The proton transfer reaction ESI-MS method utilizes amines to charge reduce the electrospray envelope of PEGs, hence PEG molecules are aminated instead of protonated. This method simplifies the mass spectrum of large PEGs, and enables the interpretation of the charge state of the observable envelopes (R ≥ 3,000 (FWHM) measured at the (M + 6H)⁶⁺ ion from 40 K PEG compound 7,324.19). Hence, deconvolution of the MS data can be performed and relative molecular masses of the individual chain lengths of the PEGs can be calculated. However, as the poly-dispersity of PEGs may vary from batch to batch and from sample to sample, it was of interest to examine if the method could distinguish between these kinds of different material. Therefore, sample materials of each intermediate obtained at five synthetic steps during synthesis of a 40 kDa PEG molecule were collected. These four intermediates, starting material and the target molecule were examined by ¹H-NMR spectroscopy and ESI-MS using a proton stripping base. The study revealed that the charge-stripping ESI-MS method is able to differentiate between even small changes in the structure of the polymeric molecules only when the analysis is assisted by ¹H-NMR spectroscopy. A proper characterization of polymer molecules requires besides relative molecular mass, also poly-dispersity and end-group characterization. No end-group information is obtained based on MS data. Examination of the PEG polymers by ¹H-NMR spectroscopy provides the needed information. In addition, the ¹H-NMR spectra clearly distinguishes the examined polymers.     

From single to multiple microcoil flow probe NMR and related capillary techniques: a review

Nuclear magnetic resonance (NMR) spectroscopy is one of the most important and powerful instrumental analytical techniques for structural elucidation of unknown small and large (complex) isolated and synthesized compounds in organic and inorganic chemistry. X-ray crystallography, neutron scattering (neutron diffraction), and NMR spectroscopy are the only suitable methods for three-dimensional structure determination at atomic resolution. Moreover, these methods are complementary. However, by means of NMR spectroscopy, reaction dynamics and interaction processes can also be investigated. Unfortunately, this technique is very insensitive in comparison with other spectrometric (e.g., mass spectrometry) and spectroscopic (e.g., infrared spectroscopy) methods. Mainly through the development of stronger magnets and more sensitive solenoidal microcoil flow probes, this drawback has been successfully counteracted. Capillary NMR spectroscopy increases the mass-based sensitivity of the NMR spectroscopic analysis up to 100-fold compared with conventional 5-mm NMR probes, and thus can be coupled online and off-line with other microseparation and detection techniques. It offers not only higher sensitivity, but in many cases provides better quality spectra than traditional methods. Owing to the immense number of compounds (e.g., of natural product extracts and compound libraries) to be examined, single microcoil flow probe NMR spectroscopy will soon be far from being sufficiently effective as a screening method. For this reason, an inevitable trend towards coupled microseparation–multiple microcoil flow probe NMR techniques, which allow simultaneous online and off-line detection of several compounds, will occur. In this review we describe the current status and possible future developments of single and multiple microcoil capillary flow probe NMR spectroscopy and its application as a high-throughput tool for the analysis of a large number of mass-limited samples. The advantages and drawbacks of different coupled microseparation–capillary NMR spectroscopy techniques, such as capillary high-performance liquid chromatography–NMR spectroscopy, capillary electrophoresis–NMR spectroscopy, and capillary gas chromatography–NMR spectroscopy, are discussed and demonstrated by specific applications. Another subject of discussion is the progress in parallel NMR detection techniques. Furthermore, the applicability and mixing capability of tiny reactor systems, termed “microreactors” or “micromixers,” implemented in NMR probes is demonstrated by carbamate- and imine-forming reactions.