A micro-volume electron capture detector for use in high resolution capillary column gas chromatography

A new design for an electron capture detector cell is described. The cell is compatible with the requirements of high resolution capillary columns and is shown to be useful in applications that require high analysis speed. A unique method of sample introduction reduces the problems of sample loss by adsorption on the surfaces of the cell. Previously reported problems of sample loss by adsorption on active surfaces within the cell when using hydrogen carrier gas are shown to have been eliminated. Examples are shown demonstrating the increased speed of analysis that can be obtained when using hydrogen carrier gas and 100 micron diameter columns.     

Fast,high resolution mass spectrometry imaging using a medipix pixelated detector

In mass spectrometry imaging, spatial resolution is pushed to its limits with the use of ion microscope mass spectrometric imaging systems. An ion microscope magnifies and then projects the original spatial distribution of ions from a sample surface onto a position-sensitive detector, while retaining time-of-flight mass separation capabilities. Here, a new type of position-sensitive detector based on a chevron microchannel plate stack in combination with a 512 × 512 complementary metal-oxide-semiconductor based pixel detector is coupled to an ion microscope. Spatial resolving power better than 6 μm is demonstrated by secondary ion mass spectrometry and 8–10μm spatial resolving power is achieved with laser desorption ionization. A detailed evaluation of key performance criteria such as spatial resolution, acquisition speed, and data handling is presented.     

Recent advances in the use of ASEDRA in post processing scintillator spectra for resolution enhancement

The ASEDRA (Advanced Synthetically Enhanced Detector Resolution Algorithm, patent pending) has been successfully applied as a post processing algorithm to both sodium iodide (NaI(Tl)) and cesium iodide (CsI(Na)) scintillator detectors to synthetically enhance their realized spectral data resolution by as much as a factor of three, wherein from these detectors the “raw” unprocessed spectra are traditionally of poor resolution. ASEDRA uses noise reduction and built-in high resolution Monte Carlo radiation transport based detector response functions (DRFs) to rapidly post-process a spectrum in a few seconds on a standard laptop; gamma lines are extracted with an accuracy that makes the scintillator detectors competitive with higher resolution, higher material cost detectors. ASEDRA differs from other tools in the field, such as Sandia’s GADRAS software, in that ASEDRA performs a differential spectrum attribution and cumulative extraction from the sample spectrum, rather than an integral-based approach, as in GADRAS. Previous publications have highlighted the successful application of ASEDRA in samples with plutonium and various isotopes. A new SmartID nuclide identification package to accompany ASEDRA has recently been implemented for test and evaluation purposes for sample attribution; in addition, the application of ASEDRA+SmartID has occurred with success in long dwell cargo monitoring and SNM detection applications, enabling new protocols for HEU detection. Overall, this paper presents recent developments and results along with a discussion of follow-on steps in the development of ASEDRA as an effective field gamma spectrum analysis tool for low cost scintillators.     

Selectivity enhancement of a metal-sensitive flame ionization detector for capillary gas chromatography

A novel modification of a hydrogen-atmosphere flamo ionization detector (HAFID) is presented which attenuates response to hydrocarbon compounds, significantly enhancing selectivity towards organometallic compounds by more than an order of magnitude. Chromatograms of an organometallic compound test mixture and regular leaded gasoline are presented to depict the specificity of the response.     

Instrument design and characterization for high resolution MALDI-MS imaging of tissue sections

In previous work, we have reported using a MALDI imaging time-of-flight mass spectrometer for the detection of protein ions from tissue sections with spatial resolution of 25 microm. We present here imaging mass spectrometry results obtained with a high-resolution scanning MALDI time-of-flight mass spectrometer, equipped with a coaxial laser illumination ion source, capable of achieving irradiation areas as small as 40 microm(2) (ca 7 microm diameter). MALDI-generated analyte ion signals from these very small irradiation volumes can be observed in a molecular weight range up to 27,000. High-resolution imaging mass spectrometry images were successfully generated from matrix thin film samples and tissue sections with scanning resolutions at and below 10 microm. This work also provides fundamental characterization of the ion signal dependence as a function of various focus and fluence parameters that will be required for extension to tissue imaging at the subcellular level.     

Carrier gas attenuation in gamma assay of radioactive xenon samples

Journal of Radioanalytical and Nuclear Chemistry - Gamma attenuation attributable to xenon and carbon dioxide carrier gas in radioactive xenon assay samples has been calculated using Monte Carlo...     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.     

Analytical calculation of the collimated detector response for the characterization of nuclear waste drums by segmented gamma scanning

Improved methods for the reconstruction of the isotope specific activity content in nuclear waste drums with data obtained by a gamma scanning system developed at Shanghai Jiao Tong University require an analytical function of the detector response. In this work we derive an analytical detector response function for a collimated HPGe detector with a square collimation window. The model is based on a purely geometric model respecting the configuration of the collimated detector system, the positions of radioactive point sources and the absorption of γ-rays in the matrix as well as in the HPGe crystal. We show that the derived analytical detector response function is in good agreement with data simulated by MCNP5.     

Isotopic analysis of uranium by neutron activation and high resolution gamma ray spectrometry

A method is described for the non-destructive and accurate determination of the isotopic composition of uranium by activation analysis. The high resolving power of Ge(Li) detectors permits easy identification on a single gamma spectrum of the gamma peaks of²³⁹Np formed from²³⁸U by activation and those of fission products formed from²³⁵U. The ratio of the peak intensities is proportional to the²³⁸U/²³⁵U ratio in the sample. A precision of ±0.6% has been obtained.     

Direct and high resolution characterization of cytochrome c equilibrium folding

Protein folding has emerged as a central problem in biophysics, and the equilibrium folding mechanism of cytochrome c (cyt c) has served as a model system. Unfortunately, the detailed characterization of both the folding process and of any intermediate that might be populated has been limited by the low structural and/or temporal resolution of the available techniques. Here, we report the use of a recently developed technique to study folding that is based on the site-selective incorporation of carbon-deuterium (C-D) bonds and their characterization by IR spectroscopy. Specifically, we synthesize and characterize the protein with deuterated residues spread throughout four structural motifs: (d3)Leu68 in the 60's helix, (d8)Lys72 and (d8)Lys73 in the 70's helix, (d8)Lys79, (d3)Met80, and (d3)Ala83 in the D-loop, and (d3)Leu94, (d3)Leu98, and (d3)Ala101 in the C-terminal helix. The data reveal correlated behavior of the residues within each structural motif, as well as between the residues of the 60's and C-terminal helices and between residues of the 70's helix and D-loop. Residues of the 70's helix and the D-loop are more stable than those within the 60's and C-terminal helices, although the former are more sensitive to added denaturant. The data also suggest that the hydrophobicity of the heme cofactor plays a central role in folding. These results contrast with those from previous H/D exchange studies and suggest that the low denaturant fluctuations observed in the H/D exchange experiments are not similar to those through which the protein actually unfolds. The inherently fast time scale of IR also allows us to characterize the folding intermediate, long thought to be present, but which has proven difficult to characterize by other techniques.     

Better characterization of surface organometallic catalysts through resolution enhancement in proton solid state NMR spectra

Delayed-acquisition methods, namely, echo and constant-time-acquisition approaches, allow a significant improvement in resolution in the proton solid state NMR spectra of surface organometallic catalysts such as [syn-(SiO)Mo(=NAr)(=CH(t)Bu)(CH2(t)Bu)] and [(SiO)Re(C(t)Bu)(=CH(t)Bu)(CH2(t)Bu)] (syn/anti ratio = 1:1). This enables the observation of all of the proton resonances, which is not possible with the simple proton single-pulse technique under magic-angle spinning. For example, the methylene protons of the neopentyl ligands, buried in the large peak associated with all of the methyls in the 1H MAS spectrum, can easily be identified by recording a delayed-acquisition spectrum (resolution enhancement of a factor of 3 is obtained). Moreover, combining constant-time acquisition with heteronuclear carbon-proton correlation spectroscopy also improves the resolution of the 2D HETCOR spectra.     

The rational use of a dynamic on-line data processing system for high and low resolution mass spectrometry

Some of the factors determining the configuration of a mass spectrometry data processing system are discussed. A rationalisation is given for a laboratory situation dealing with a variety of mass spectrometric problems. The effective use of a dynamic on-line system in such an environment is demonstrated. Conversational procedures are described for the acquisition, reduction and interpretation of mass spectral data, using a CRT visual display terminal as a fast man-computer interactive communication medium.     

Mixing enhancement for high viscous fluids in a microfluidic chamber

Due to small channel dimensions and laminar flows, mixing in microfluidic systems is always a challenging task, especially for high viscous fluids. Here we report a method of enhancing microfluidic mixing for high viscous fluids using acoustically induced bubbles. The bubbles can be generated in an acoustically profiled microfluidic structure by using a piezoelectric disk activated at a working frequency range between 1.5 kHz and 2 kHz. The mixing enhancement is achieved through interactions between the oscillating bubbles and fluids. Both experimental studies and numerical simulations are conducted. In the experiments, DI water-glycerol mixture solutions with various viscosities were used. The results, based on the mixing efficiency calculated from experimentally acquired fluorescent images, showed that good mixing can occur in the DI water-glycerol solutions with their maximum viscosity up to 44.75 mPa s, which to our best knowledge is the highest viscosity of fluids in microfluidic mixing experiments. To explain the mechanisms of bubble generation, the numerical simulation results show that, corresponding to the actuations at the working frequency range used in the experiment, there exists a low pressure region where the pressure is lower than the water vapor pressure in the DI water-glycerol solutions, resulting in the generation of bubbles.     

Evaluation of electron capture cell designs for use in high resolution capillary column gas chromatography

A comparison of the effects on peak shape is made between a 350 and 100 microliter displaced coaxial and a 350 microliter concentric cylinder electron capture cell. Peaks as fast as W_1/2 = 0.5 second were detected using electronics operating in the constant current mode. The measured peak shapes are compared to those obtained by computer simulation assuming either complete mixing or plug-like flow within ECD cell. The advantage of controlling the flow pattern through the cell to obtain plug-like flow is demonstrated. Differences in peak shape between the displaced coaxial and concentric cylinder cells of the same volume are explained in terms of the electrostatic fields within the cells.     

The use of non-destructive high energy gamma photon activation for trace element survey analysis

An empirical study has been made of the potential of high energy γ photon activation and high resolution γ-ray spectrometry for the survey analysis of trace elements in a variety of materials. Human blood, urine, bone ash, standard glass (NBS, SRM 612) and air particulates, along with synthetic multi-element standards, have been studied following irradiation with γ photons of maximum energy 17–45 MeV. Elements found to be suited to determination by γ activation include Sb, As, Bi, Cd, Cs, Ca, Ce, Cr, Fe, Au, Pb, Mg, Mo, Ni, Nb, Rb, Sr, Tl, Ti, Tm, Zn and Zr. γ spectra, elemental concentrations measured, and/or limits of detection observed, for the matrices studied are given.     

Performance of a portable, electromechanically-cooled HPGe detector for site characterization

Characterization is a first step to site cleanup or decommissioning of a disused nuclear facility. Good knowledge of the inventory of nuclides present, both type and location, is important in the design of an effective plan of remediation. Several systems based on HPGe detectors have been developed, both commercially and at laboratories, and are already in use for this purpose. Their use is somewhat complicated by the need for cryogenic cooling of the HPGe detector. Handling of liquid nitrogen in field situations is always difficult. Recent developments in low-power electromechanical cooling for HPGe detectors have made possible the construction of low weight, portable HPGe spectrometers with sufficient efficiency to perform the needed measurements in reasonable count times, without the need for liquid nitrogen. A mobile system was modified to use a battery-powered, Sterling-engine cooler on a nominal 40% relative efficiency detector. This system was characterized for efficiency and uniformity of response. The baseline spectra were analyzed using the DOE EML 1-meter methods to obtain representative MDA values for several nuclides of interest and typical counting times.     

Polyolefin characterization in dibutoxymethane by high temperature gel permeation chromatography with a new evaporative light scattering detector

A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different types of polyolefins (polypropylene, linear and low-density polyethylene) in dibutoxymethane (DBM, butylal). These samples were previously characterized by GPC in trichlorobenzene (TCB) with a differential refractive index (DRI) detector in an interlaboratory study conducted by the International Union of Pure and Applied Chemistry (IUPAC) [1], and in a recent publication by GPC with the new ELSD in TCB [2]. The signal to noise of ELSD using DBM is about 10 times lower than that for TCB. However, the ELSD signal power exponent for DBM was measured as 1.35, which is much closer to unity than the value of 1.61 for TCB. After applying the required corrections to linearize the response of the ELSD signal as a function of concentration, similar average molecular weights to those measured in the interlaboratory study using DRI, were obtained for the analyzed resins.     

Complementary mobile-phase optimisation for resolution enhancement in high-performance liquid chromatography

An optimisation methodology in high-performance liquid chromatography (HPLC) is presented for the selection of two or more mobile phases having an optimal complementary resolution. The complementary mobile phases (CMPs) are selected in such a way that each one resolves optimally only some compounds in the mixture, while the remainder, resolved by the other mobile phase(s), can overlap among them. The methodology is based on the computation of a peak purity measurement for each solute, using an asymmetrical peak model for peak simulation. Two global resolution criteria (product of elementary resolutions and worst elementary resolution) and two methods for solving the problem (a systematic examination of all possible solute arrangements, and the use of genetic algorithms to expedite the calculation time) were used to find the optimal CMPs. The CMP optimisation methodology was applied to the resolution of a mixture of 10 diuretics and beta-blockers, which could not be resolved using a single mobile phase; virtual baseline resolution was achieved, however, with two CMPs.