Isotope pattern geometry challenge.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
Juris Meija
Publications and source records attributed to Juris Meija.
Chemical logic challenge.
Explore the source record for details and available documents.
Journal Article↗
Retention of Cr(III) by high-performance chelation ion chromatography interfaced to inductively-coupled plasma mass spectrometric detection with collision cell.
High-performance chelation ion chromatography (HPCIC) was employed to retain cationic Cr(III) on an anion-exchange column and hence allow the separation of the two most prevalent forms of chromium, Cr(II) and Cr(VI). A mobile phase of nitric acid was utilized at pH = 1.5; additionally, 2,6-pyridinedicarboxylic acid was used at a concentration of 6 mM. Additives with different structural characteristics were used in an effort to elucidate retention mechanisms. Inductively-coupled plasma mass spectrometry was used for chromium detection. A collision cell was utilized to reduce chloride-based polyatomic ions that may interfere with the detection of Cr(III), and a detection limit study yielded levels in the low part-per-billion range. The newly developed method was applied to the chromatographic analysis of samples of an incubation medium containing Cr(VI) incubated with cell nuclei.
Animals↗
Preliminary studies on selenium-containing proteins in Brassica juncea by size exclusion chromatography and fast protein liquid chromatography coupled to ICP-MS.
An approach for screening and resolving selenium-containing plant proteins was developed based on the combination of sample preparation and multi-dimensional liquid chromatography coupled to ICP-MS. Different protein extraction protocols were investigated. A 24 h dodecylsulfate-mediated protein extraction in a sonication bath followed by acetone precipitation was found to be optimal. The use of different protein precipitate solubilizing agents (sodium dodecyl sulfate media and Tris-HCl buffer) demonstrates possible fractionation of the selenium-containing proteins. Selenium-containing protein screening and fractionation were carried out by means of SEC-ICP-MS. High molecular weight selenium containing proteins were solubilized with a sodium dodecyl sulfate-containing buffer, whereas the low molecular weight compounds were released into a Tris-HCl buffer. Size exclusion chromatography-fast protein liquid chromatography coupled to ICP-MS allowed separation and detection of several selenium-containing proteins in Se-supplemented wild type Brassica juncea plant, a fast growing selenium accumulator.
Chromatography, Gel↗
Deconvolution of isobaric interferences in mass spectra.
The concept of isobar deconvolution using the mass domain and signal intensity based domains is described. The intensity domain-based approach employs the reconstruction of the observed isotope pattern from the isolated patterns of the isobaric species. The quantitative information is adjusted with the use of the least squares algorithm. The mass domain-based approach employs signal deconvolution by forming Gaussian components for which the peak width and position can be predicted a priori. The latter method is applicable to medium resolution instruments, such as TOF-MS, while the pattern reconstruction approach is applicable also to low resolution instrumentation, such as quadrupole-based ICP-MS or GC/MS. An example of CH(z)Se (z = 0-4) cluster analysis in dimethyl diselenide mass spectra is given to illustrate the concepts underlying both approaches.
Algorithms↗
Interpretation of alkyl diselenide and selenosulfenate mass spectra.
The mass spectral fragmentation of aliphatic diselenides and selenosulfenates is analyzed to gain a better understanding of the behavior of these species. The main fragmentation pathways of these species include the fragmentation along the Se?C bond, fragmentation along the Se?Se or Se?S bonds and intra-molecular rearrangements. In general, negative ionization favors the fragmentation along the Se?Se or Se?S bonds while positive ionization leads to stable molecular ions. Density functional theory calculations of bond dissociation energies and molecular orbital analysis was undertaken to explain the observed trends in molecular fragmentation. Besides the analysis of molecular fragmentation, a phenomenon of molecular association in negative electron impact and positive chemical ionization conditions was observed and investigated using a high resolution time-of-flight mass spectrometer. Molecular association that occurs during the ionization of species includes the formation of symmetrical diselenides from asymmetrical selenosulfenates and formation of alkylseleno adducts from the corresponding diselenides. For species which is hard to resolve by mass analysis, such as isobars of CHSe, CH(2)Se, and CH(3)Se, the isotope pattern superimposition procedure was applied to define the overlapping clusters.
Ions↗
Phenyl-terminated fatty acids in seeds of various aroids.
A series of homologous omega-phenylalkanoic acids and omega-phenylalkenoic acids were isolated from seed lipids of various genera of the subfamily Aroideae of Araceae (the Jack-in-the-Pulpit family) and characterized. Besides the major acids, 11-phenylundecanoic acid, 13-phenyltridecanoic acid and 15-phenylpentadecanoic acid, all other homologous odd carbon number omega-phenylalkanoic acids from C7 to C23 were detected in trace amounts. Additionally, one even carbon number acid, 12-phenyldodecanoic acid was found in several specimens in trace amounts. Similarly, two series of homologous odd carbon number monounsaturated omega-phenylalkenoic acids were found and characterized using dimethyl disulfide derivatization to locate the positions of their double bonds. In five acids from C11 to C19, the double bond is located at the same distance, A7, from the phenyl ring. In the other two acids of C13 and C15 chain length, the double bond is located at delta5 from the phenyl ring.
Araceae↗
Speciation of volatile selenium species in plants using gas chromatography/inductively coupled plasma mass spectrometry.
Gas chromatography/inductively coupled plasma mass spectrometry (GC/ICP-MS) coupled with solid phase micro-extraction can provide a simple, extremely selective and sensitive technique for the analysis of volatile sulfur and selenium compounds in the headspace of growing plants. In this work, the technique was used to evaluate the volatilization of selenium in wild-type and genetically-modified Brassica juncea seedlings. By converting toxic inorganic selenium in the soil to less toxic, volatile organic selenium, B. juncea might be useful in bioremediation of selenium contaminated soil.
Brassica↗
Overexpression of selenocysteine methyltransferase in Arabidopsis and Indian mustard increases selenium tolerance and accumulation.
A major goal of phytoremediation is to transform fast-growing plants with genes from plant species that hyperaccumulate toxic trace elements. We overexpressed the gene encoding selenocysteine methyltransferase (SMT) from the selenium (Se) hyperaccumulator Astragalus bisulcatus in Arabidopsis and Indian mustard (Brassica juncea). SMT detoxifies selenocysteine by methylating it to methylselenocysteine, a nonprotein amino acid, thereby diminishing the toxic misincorporation of Se into protein. Our Indian mustard transgenic plants accumulated more Se in the form of methylselenocysteine than the wild type. SMT transgenic seedlings tolerated Se, particularly selenite, significantly better than the wild type, producing 3- to 7-fold greater biomass and 3-fold longer root lengths. Moreover, SMT plants had significantly increased Se accumulation and volatilization. This is the first study, to our knowledge, in which a fast-growing plant was genetically engineered to overexpress a gene from a hyperaccumulator in order to increase phytoremediation potential.
Adaptation, Physiological↗
Studies of selenium-containing volatiles in roasted coffee.
Coffee has been an important and heavily used beverage in many cultures over a long period of time. Although sulfur species have been found to be abundant constituents, no work to date has explored the presence of selenium analogues. Investigation of volatile selenium species from green coffee beans, roasted beans, and brewed coffee drink was performed using solid phase microextraction (SPME) sample preconcentration in conjunction with GC/ICP-MS. Several volatile selenium species at trace levels were detected from roasted coffee beans as well as in the steam from brewed coffee drinks. No detectable selenium (and sulfur) species, however, were found in the headspace of green beans, indicating that selenium-containing volatiles are formed during roasting, as is the case for the sulfur volatiles. Matching standards were prepared and used to identify the compounds found in coffee. Artificial supplementation of the green coffee beans with selenium before roasting was performed to further characterize the selenium-containing volatiles formed during the coffee-roasting process.
Coffea↗
Simultaneous monitoring of volatile selenium and sulfur species from se accumulating plants (wild type and genetically modified) by GC/MS and GC/ICPMS using solid-phase microextraction for sample introduction.
A sensitive method for determining ultratrace volatile Se species produced from Brassica juncea seedlings is described. The use of a new commercially available GC/ ICPMS interface in conjunction with solid-phase micro-extraction is a promising way to perform these studies. The addition of optional gases (O2 and N2) to the argon discharge proved to increase the sensitivity for Se and S as well as for Xe, which as a trace contaminant gas, was used for ICPMS optimization studies. However, the optimization parameters differ when an optional gas is added. In the best conditions, limits of detection ranging from 1 to 10 ppt can be obtained depending on the Se compound and 30 to 300 ppt for the volatile S species. The use of GC/MS with similar sample introduction permits the characterization of several unknown species produced as artifacts from the standards. The method allows the virtually simultaneous monitoring of S and Se species from the headspace of several plants (e.g., onions, garlic, etc.) although the present work is focused on the B. juncea seedlings grown in closed vials and treated with Se. Dimethyl selenide and dimethyl diselenide were detected as the primary volatile Se components in the headspace. Sulfur species also were present as allyl (2-propenyl) isothiocyanate and 3-butenyl isothiocyanate as characterized by GC/MS.
Brassica↗
Plasma spectrometry for elemental speciation and characterization in beverages.
A review is presented on recent applications of plasma spectrometric techniques for speciation analysis in beverages. The 3 most common ways of characterizing beverages in addition to elemental speciation are also discussed: total element analysis, isotope ratio, and statistical characterization. To date, most of the elemental characterization in beverages with plasma techniques has been performed in the statistical evaluation of wines and in teas. However, despite the increasing interest in elemental speciation, most of the plasma-based techniques in beverage studies are used for total metal detection and the full capabilities of inductively coupled plasma techniques have yet to be realized.
Beer↗