Can instrumental neutron activation analysis keep pacewith the needs of the high purity materials industry?

The University of Missouri Research Reactor Center (MURR) has been one of the premier providers of neutron activation analysis (NAA) to the high purity materials industry for the past 20 years. Over the last two decades, significant advances in contamination control in the manufacturing process and the development of alternate analytical techniques have challenged the NAA community to keep pace. This paper presents an overview of the High Purity Materials Analysis Program at MURR. Specifically we present trends in the trace element concentrations that we have observed in our laboratory over the past 10 years and compare our experience with the relevant literature. The prospects for the future success of NAA and the methodological changes required for satisfying the industry's need will be discussed.     

Differences in trace element concentrations between Alzheimer and “normal” human brain tissue using instrumental neutron activation analysis (INAA)

Brain samples obtained from the Netherlands Brain Bank were taken fromthe superior frontal gyrus, superior parietal gyrus and medial temporal gyrusof 'normal' and Alzheimer's disease subjects in order todetermine elemental concentrations and compare elemental composition. Brainsamples from the cortex were taken from 18 subjects, eight 'normals'(6 males and 2 females) and eleven with Alzheimer's disease, (1 maleand 10 females) and the following elemental concentrations, Na, K, Fe, Zn,Se, Br, Rb, Ag, Cs, Ba, and Eu were determined by instrumental neutron activationanalysis (INAA). The element which showed the greatest difference was Br,which was found to be significantly elevated in the cortex of Alzheimer'sdisease brains as compared to the 'normals' at significance (p<0.001).     

Determination of As by instrumental neutron activation analysis in sectioned hair samples for forensic purposes: chronic or acute poisoning?

Autopsy of 29-year old woman suspicious of committing suicide by the ingestion of As₂O₃ yielded contradictory findings. All pathological findings as well as clinical symptoms suggested acute poisoning, while a highly elevated As level of 26.4 μg g⁻¹ in her hair collected at the autopsy, which was determined with inductively coupled plasma mass spectrometry indicated chronic poisoning. To elucidate this discrepancy, instrumental neutron activation analysis (INAA) with proven accuracy was performed of another set of sectioned hair samples. Levels of As found by INAA in the range of 0.16–0.26 μg g⁻¹ excluded chronic poisoning, because the person died after approximately 14 h after the As₂O₃ ingestion. Two reasons for the discordant As results obtained by ICP-MS and INAA are considered: (1) accidental, non-removed contamination of hair on the As₂O₃ ingestion; (2) erroneous performance of ICP-MS.     

Assessment of metal and trace element concentrations in the Cananéia estuary,Brazil, by neutron activation and atomic absorption techniques

Twenty six bottom sediment samples were collected from the Cananéia estuary in summer and winter of 2005. Multielemental analysis was carried out by instrumental neutron activation analysis. Total mercury was determined by cold vapor atomic absorption. As, Cr, Hg and Zn concentrations were compared to the Canadian oriented values (TEL and PEL). Sample points 4 and 9 presented higher concentration for most elements and As and Cr exceeded the TEL values. Organic matter (>10%) associated with siltic and clay sediments was observed. Climatic conditions, hydrodynamic and biogeochemical processes promote differences in seasonal concentrations of elements at some points, which contribute to special distributions.     

Uptake of oxygen in a coal standard reference material® determined by fast (14-MeV) neutron activation analysis

A fast (14-MeV) neutron activation analysis procedure was employed to directly measure mass fractions of oxygen in coal samples. The procedure demonstrated sufficient precision and accuracy to determine a relative change of about 5% or more, in the oxygen mass fraction of about 12%. The procedure was applied to test samples of the newly developed SRM 1632c Trace Elements in Coal (Bituminous). The samples had been stored at three conditions: in liquid nitrogen vapor and at room temperature in the original containers packaged under argon, and for accelerated aging at 50 °C open to air. Following six months storage increments, duplicate samples of each of twelve bottles of the SRM were measured for each storage condition. In addition each sample was processed through ten separate analytical runs yielding a total of some 720 measurements per storage duration. Oxygen was determined by comparison to a primary standard potassium dichromate and the accuracy of the method was assessed through the analysis of replicate samples of three reference materials that are certified for oxygen content. The initial 6-months test period indicated uptake of oxygen in the open-air storage.     

Analysis of wines by ICP-MS: Is the pattern of the rare earth elements a reliable fingerprint for the provenance?

In a comparative analysis of young and finished product wines by semi-quantitative ICP-MS, a striking difference was observed: finished products exhibited significant concentrations of the rare earth elements whereas the concentrations in young wines which had not been subdued to any treatment after their initial preparation from the grapes were below the determination limits with a quadrupole instrument and could only be determined with a magnetic field instrument operated at a low mass resolution (R = 300). The reason was found in contamination from bentonites as usually applied for the purification of wines from tarnishing components such as proteins. Therefore, bentonites of different origin were extracted with a reference wine, and an increase of the rare earth element concentrations by more than one order of magnitude was observed in the extracts. The investigation leads to the conclusion that the concentration pattern of the rare earth elements can be strongly affected by the wine producing process and therefore is not generally suitable as a fingerprint for the provenance of wines. Received: 3 December 1998 / Revised: 11 February 1999 / Accepted: 18 February 1999     

Brönsted acid hydrotrope combined catalysis in water: a green approach for the synthesis of indoloquinoxalines and bis-tetronic acids

The present work describes the applications of Brönsted acid hydrotrope combined catalyst (BAHC) as a mild, efficient and reusable catalyst for synthesis of indoloquinoxalines and bis-tetronic acids in water. Using BAHC, we synthesized many indoloquinoxaline derivatives from isatins and o-phenylene diamine using 10 mol% PTSA in 40% aqueous hydrotropic (NaPTS) solution at room temperature with 83–90% yields. On the other hand, the reaction of tetronic acid with the aldehydes/isatins forms bis-tetronic acids with 83–88% yields through Knoevengel condensation-Michael addition pathway in same BHAC. Moreover, the BAHC can be recycled upto 5th cycles with slight decrease in product yields. The extremely simple operational methodology, green solvent, ambient reaction conditions and high yields render this approach extremely appealing for the synthesis of different heterocyclic compounds.

     

Characterization of neutron spectrum at Es-Salam Research Reactor using Høgdahl convention and Westcott formalism for the k<Subscript>0</Subscript>-based neutron activation analysis

For the general applicability of the k ₀-NAA method two formalisms were carried out to deal with “1/ν and non-l/ν ((n,γ)” reaction nuclides, respectively. In the Høgdahl-formalism the reactor neutron spectrum parameters, such as α and f were measured using three methods: Cd-ratio, Cdcovered and bare triple monitors. In addition, bare bi-isotopic method using Zr is also utilized for the calculation of f. According to the Westcottformalism the modified spectral index r(α)√T _n /T ₀ and g(T _n ) factor for monitoring neutron temperature T _n , were measured employing Lu as non “1/v” monitor and ¹⁹⁷Au, ⁹⁶Zr and ⁹⁴Zr as “1/v” monitors. The reduced resonance integral of lutetium s _0,Lu was also calculated. To evaluate the applicability of k ₀-NAA in our analytical system, the analysis of two kinds of SRMs was executed. The analytical results showed that the relative error of most of the elements was less than 10%.     

DFT analysis of the activation and breaking of the Mo-N bond in a (mu-nitrido)dimolybdenum complex: is molybdenum tris(thiolate) an elusive intermediate?

The electronic structure, conformation, synthesis, and thermal decomposition pathways of the recently characterized dimolybdenum mu-nitrido complex (AdS)(3)Mo(mu-N)Mo(N[(t)Bu]Ph)(3) (1exp, Ad = adamantyl) are investigated by means of DFT calculations carried out on the model system (HS)(3)Mo(mu-N)Mo(NH(2))(3) (1). The observed asymmetry of the Mo(mu-N)Mo core is reproduced in the optimal conformation of 1 and assigned to the tendency for the electron density of the metal atoms to be preferably accommodated in the pi orbitals of Mo(thiolate). The balance in the metal-ligand and ligand-ligand interactions conditioning the flow of the electron density along the Mo-(mu-N)-Mo framework, and eventually the relative activation of the molybdenum-nitrido bonds, appears very sensitive to the nature of the ancillary substituents on both the thiolate and the amido sides. On one hand, replacing HS by AdS in 1 increases the calculated value of Delta(mu-N-Mo) from 0.053 to 0.094 A, close to the experimental value of 0.111 A. The mu-nitrido complex with bulky thiolates 1a is also less stable than 1 by 7.3 kcal x mol(-1) with respect to its monometallic constituents. On the other hand, substituting the bulky N[(t)Bu]Ph for NH(2) in the model complex 1b induces an important charge transfer toward the thiolate moiety resulting in structural and energetic consequences of similar magnitude. Even though these substitutional effects are not likely to be fully additive in the real complex, both should contribute to an increase of the mu-N-Mo(thiolate) bond activation in 1exp. The importance of this activation conditions the feasibility of the thermal decomposition of 1exp promoted by benzonitrile which eventually yields the molybdenum thiolate dimer (RS)(3)Mo [triple bond] Mo(SR)(3). The energy profile calculated for this reaction with model complex1 in the presence of one or two molecules of acetonitrile shows that the axial fixation of the promoter on one or both molecular ends forms intermediates in which the mu-N-Mo(thiolate) bond is further activated with respect to the original complex. The consequence is an important, but still insufficient, decrease of the barrier to Mo-N bond breaking, from 53 to 37 kcal x mol(-1). Furthermore, the thermodynamic balance of the reaction leading from the acetonitrile adducts of 1 to (HS)(3)Mo [triple bond] Mo(SH)(3) remains endothermic by 6.5 kcal x mol(-1) for the monoadduct, and more for the diadduct. It therefore appears that bulky substituents on both ends of the dinuclear complex are essential to the completion of the reaction, from both the thermodynamic and the kinetic viewpoints.     

Synchrotron radiation total reflection X-ray fluorescence and energy dispersive X-ray fluorescence analysis on AP1™ films applied to the analysis of trace elements in metal alloys for the construction of nuclear reactor core components: a comparison

Synchrotron radiation induced total reflection X-ray fluorescence and conventional 45° energy dispersive X-ray fluorescence analysis using a 150-nm-thick AP1™ film as sample carrier have been exploited for the elemental analysis of traces in alloys used for the construction of reactor core components of nuclear power plants. Both techniques are well suited for the analysis since they require a low amount of sample (μl), important on one hand because of the limited disposal and on the other hand because of its high specific activity. The methods provide a very low background due to the total reflection phenomenon in TXRF and the thin AP1™ film sample support, respectively. The employment of synchrotron radiation was necessary since there are no laboratory sources which can deliver a collimated beam of the energy and intensity needed to excite the K-shell of the rare earth elements, allowing the achievement of minimum detection limits relevant for the proposed purpose (ng/g range). Moreover, the linear polarization of synchrotron radiation combined with a side-looking detection geometry manages to reduce the scattering due to the remaining matrix of the analyzed samples. Detection limits for Nb and for some of the rare earth elements (pg range for absolute detection limits and ng–μg/g range for concentration detection limits) obtained with the two techniques are presented and the two approaches are compared.     

Study of the relationship of small variations of the molecular structure and the iron state in iron containing proteins by Mössbauer spectroscopy: biomedical approach

This review considers the results of experimental M?ssbauer studies and theoretical calculations of the effect of small variations of protein molecular structure on the iron electronic structure and stereochemistry in order to understand the proteins structural heterogeneity and functional variety. Structural changes in iron containing proteins during various diseases are also considered. These results show the relationship of the small structural variations and M?ssbauer parameters of iron containing proteins and demonstrate the possibilities of M?ssbauer spectroscopy to obtain new information at the molecular level in biomedical research.     

Analysis of paint cross-sections: a combined multivariate approach for the interpretation of μATR-FTIR hyperspectral data arrays

The present research is aimed at introducing a suitable approach for the exploitation of the hyperspectral data obtained by μATR-FTIR analyses of paint cross-sections. The application of principal component analysis for chemical mapping is well-established, even if a very limited number of applications to μFTIR data have been reported so far in the field of analytical chemistry for cultural heritage. Moreover, in many cases, chemometric tools are under-utilized and the outcomes under-interpreted. As a consequence, results and conclusions may be considerably compromised. In an attempt to overcome such drawbacks, the present work is proposing a comprehensive and efficient procedure based on an interactive brushing approach, which combines the structural information of the score scatter plots and the spatial information of the principal component (PC) score maps. In particular, the study demonstrates not only how the multivariate approach may provide more information than the univariate one, but also how the integration of different chemometric tools may allow a more comprehensive interpretation of the results with respect to the studies up to now reported in the literature. The examination of the average spectral profile of each score cluster, jointly with the loading analysis, is functional to characterize each area investigated on the basis of its spectral features. A multivariate comparison with spectra of standard compounds, projected in the PC score space, helps in supporting the chemical identification. The approach was validated on two real case studies.     

An entry to the azocino[4,3-b]indole framework through a dehydrogenative activation of 1,2,3,4-tetrahydrocarbazoles mediated by DDQ: formal synthesis of (±)-uleine

It is presented that hexahydro-1,5-methano[4,3-b]indoles were efficiently synthesized in high yields (up to 89% yield) through the cyclization reaction of starting tetrahydrocarbazoles bearing a monoalkylaminocarbonylmethyl moiety at the C-2 position mediated by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). A mechanistic proposal is also given that mainly includes two cascade reactions: (i) formation of a vinylogous iminium cation via DDQ-mediated dehydrogenation of tetrahydrocarbazole functionality and (ii) intra-molecular and syn-selective addition of the amide functionality as the nucleophile to the vinylogous iminium cation. Furthermore, this cyclization reaction was successfully utilized in the formal total synthesis of (±)-uleine, an Aspidospermatan skeletal type alkaloid.     

Gas chromatography–triple quadrupole tandem mass spectrometry: a powerful tool for the (ultra)trace analysis of multiclass environmental contaminants in fish and fish feed

A new method for rapid determination of 73 target organic environmental contaminants including 18 polychlorinated biphenyls, 16 organochlorinated pesticides, 14 brominated flame retardants and 25 polycyclic aromatic hydrocarbons in fish and fish feed using gas chromatography coupled with triple quadrupole tandem mass spectrometry (GC–MS/MS) was developed and validated. GC–MS/MS in electron ionization mode was shown to be a powerful tool for the (ultra)trace analysis of multiclass environmental contaminants in complex matrices, providing measurements with high selectivity and sensitivity. Another positive aspect characterizing the newly developed method is a substantial simplification of the sample preparation, which was achieved by an ethyl acetate QuEChERS (quick, easy, cheap, effective, rugged and safe) based extraction followed by silica minicolumn clean-up. With use of this sample preparation approach the sample laboratory throughput was increased not only because six samples may be prepared in approximately 1 h, but also because all the above-mentioned groups of contaminants can be determined in a single GC–MS/MS run. Under the optimized conditions, the recoveries of all target analytes in both matrices were within the range from 70 to 120 % and the repeatabilities were 20 % or less. The method quantification limits were in the range from 0.005 to 1 μg kg^–1 and from 0.05 to 10 μg kg^–1 for fish muscle tissue and fish feed, respectively. The developed method was successfully applied to the determination of halogenated persistent organic pollutants and polycyclic aromatic hydrocarbons in fish and fish feed samples.     

Kinetic analysis of the phenyl-shift reaction in β-O-4 lignin model compounds: a computational study

The phenyl-shift reaction for the β-radical of phenethyl phenyl ether (PhCH(2)C?HOPh, β-PPE) is an integral step in the pyrolysis of PPE, which is a model compound for the β-O-4 linkage in lignin. We investigated the influence of natural occurring substituents (hydroxy, methoxy) on the reaction rate by calculating relative rate constants using density functional theory in combination with transition state theory, including anharmonic correction for low-frequency modes. The phenyl-shift reaction proceeds through an oxaspiro[2.5]octadienyl radical intermediate and the overall rate constants were computed invoking the steady-state approximation (its validity was confirmed). Substituents on the phenethyl ring have only little influence on the rate constants. If a methoxy substituent is located in the para position of the phenyl ring adjacent to the ether oxygen, the energies of the intermediate and second transition state are lowered, but the overall rate constant is not significantly altered. This is a consequence of the dominating first transition from reactant to intermediate in the overall rate constant. In contrast, o- and di-o-methoxy substituents significantly accelerate the phenyl-migration rate compared to β-PPE.     

Conformational analysis and interpretation of ν(OH) band in the IR spectrum of o-vinylphenol: a DFT study

Two-dimensional cyclic potential energy surface for internal rotation of vinyl and hydroxyl substituents in o-vinylphenol molecule was constructed by the B3LYP/6-311G(d) method. It was shown that o-vinylphenol molecule exists in the gas phase as a mixture of seven rotamers denoted as A (A′), B (B′), C (C′) and D. The B3LYP/cc-pVTZ calculated percentage of the rotamers A and A′ in which OH…π intramolecular interaction occurs, is at most 24%. The height of barriers t interconversions between o-vinylphenol rotamers varies from 0.1 to 5.2 kcal mol⁻¹. According to B3LYP/cc-pVTZ calculations, the inclusion of solvent effect in the framework of the polarizable continuum model for a solution of o-vinylphenol in CCl₄ leads to a decrease in theoretical values of ν(OH) frequencies by about 4–9 cm⁻¹ and to an increase in the percentage of the rotamers without intramolecular hydrogen bond by about 4.3% compared to the corresponding gas-phase values. The simulated IR spectral contours of ν(OH) bands are in good agreement with experimental one Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 499–508, March, 2008.     

Ambiphilic dual activation role of a task-specific ionic liquid: 2-hydroxyethylammonium formate as a recyclable promoter and medium for the green synthesis of β-nitrostyrenes

A cost-effective task-specific ionic liquid, 2-hydroxyethylammonium formate, efficiently promotes the condensation of nitroalkanes with various aldehydes to produce β-nitrostyrenes in high to excellent yields at room temperature. This reaction does not involve any hazardous organic solvent and toxic catalyst. The ionic liquid is recovered and recycled for subsequent reactions. In addition, a novel mechanism has been proposed invoking ambiphilic dual activation influence of the ionic liquid.     

Development of a chiral micellar electrokinetic chromatography–tandem mass spectrometry assay for simultaneous analysis of warfarin and hydroxywarfarin metabolites: Application to the analysis of patients serum samples

The enantioseparation of warfarin (WAR) along with the five positional and optical isomers is challenging because of the difficulty to simultaneously separate and quantitate these chiral compounds. Currently, no effective chiral CE–MS methods exist for the simultaneous enantioseparation of WAR and all its hydroxylated metabolites in a single run. Polymeric surfactants (aka. molecular micelles) are particularly compatible with micellar electrokinetic chromatography–mass spectrometry (MEKC–MS) because they have a wider elution window for enantioseparation and do not interfere with the MS detection of chiral drugs. Using polysodium N-undecenoyl-l,l-leucylvalinate (poly-l,l-SULV) as a chiral pseudophase in MEKC–MS baseline separation of WAR, its five metabolites along with the internal standard was obtained in 45 min. This is in comparison to 100 min required for separation of the same mixture with packed column CEC–MS using a vancomycin chiral stationary phase. Serum samples were extracted with mixed-mode anion-exchange (MAX) cartridge with recoveries of greater than 85.2% for all WAR and hydroxywarfarin (OH-WAR) metabolites. Utilizing the tandem MS and multiple reaction monitoring mode, the MEKC–MS/MS method was used to simultaneously generate calibration curves over a concentration range from 2 to 5000 ng/mL for R- and S-warfarin, 5 to 1000 ng/mL for R- and S-6-, 7-, 8- and 10-OH-WAR and 10 to 1000 ng/mL for R and S-4′-OH-WAR. For the first time, the limits of detection and quantitation for most WAR metabolites by MEKC–MS/MS were found to be at levels of 2 and 5 ng/mL, respectively. The method was successfully applied for the first time to analyze WAR and its metabolites in plasma samples of 55 patients undergoing WAR therapy, demonstrating the potential of chiral MEKC–MS/MS method to accurately quantitate with high sensitivity.