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Biomedical subjects

Juris Meija

Publications and source records attributed to Juris Meija.

At least 19 recordsLinked to original sources
PubMed2005

Determination of phosphoric acid triesters in human plasma using solid-phase microextraction and gas chromatography coupled to inductively coupled plasma mass spectrometry.

A simple and sensitive method for determination of phosphoric acid triesters at trace levels in human plasma sample is described. In this work, solid-phase microextraction (SPME) is employed as a sample preparation procedure for extraction and pre-concentration of alkyl and aryl phosphates followed by gas chromatography coupled to inductively coupled plasma mass spectrometry (GC-ICP-MS) for phosphorus-specific and very sensitive determination of these compounds in human plasma. The detection limits from blood plasma were 50 ngL(-1) (tripropyl phosphate), 17 ngL(-1) (tributyl phosphate), 240 ngL(-1) (tris(2-chloroethyl) phosphate) and 24 ngL(-1) (triphenyl phosphate). Sample preparation involves plasma deproteinization followed by direct immersion SPME with 65 microm poly(dimethylsiloxane/divinylbenzene) fiber. Extraction was performed at 40 degrees C for 30 min and at pH 7.0 in 10 mM sodium carbonate buffer. The reported method, to our knowledge, describes the first application of SPME with element-specific detection for analysis of phosphoric acid esters. Application of the method to the plasma samples, previously stored in poly(vinyl chloride) plasma bags revealed the presence of triphenyl phosphate, which was further confirmed by SPME GC time-of-flight high-resolution mass spectrometry.

Chemical Fractionation↗
PubMed2005

Strategies to study human serum transferrin isoforms using integrated liquid chromatography ICPMS, MALDI-TOF, and ESI-Q-TOF detection: application to chronic alcohol abuse.

Variations in the distribution of sialoforms of human serum transferrin (Tf) in correlation with pathological states, which are associated with abnormalities in glycosylation, is of great clinical interest. In such studies, the methodologies of analysis are required to be sensitive and selective for observing small variations among isoforms and able to characterize the molecular structure of such forms. Thus, the present work describes, in the first part, the separation of transferrin isoforms, after iron saturation of the protein, by high-performance liquid chromatography (HPLC) and the on-line specific atomic detection of the iron present on each of the separated isoforms by on-line coupling the HPLC system to an inductively coupled plasma mass spectrometer (ICPMS). This allowed low detection levels for the different isoforms (L.D. 0.03 microMTf). After screening of the isoforms containing iron by ICPMS, structural characterization of each isoform can be independently carried out. Thus, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF) and electrospray mass spectrometry (ESI-Q-TOF) are compared in the second part of this study. The different atomic and molecular MS methods revealed the presence of elevated carbohydrate-deficient transferrin (CDT) isoforms in human serum samples from chronic alcohol consumption patients. MALDI-TOF appeared to be sensitive to concentration levels of the analytes, and the observed mass accuracy was highly compromised by the protein heterogeneity (peak width at half-maximum approximately 2000 Da for every fraction). On the other hand, ESI-Q-TOF allowed good mass accuracy (m < or = 0.05%) and peak width of 45 Da in the deconvoluted spectra; while ICPMS detection could be preferable for sensitive protein isoforms determinations, ESI-Q-TOF turns out to be an excellent "fingerprinting" technique for alcoholism diagnosis.

Alcoholism↗
PubMed2005

Interpretation of butyltin mass spectra using isotope pattern reconstruction for the accurate measurement of isotope ratios from molecular clusters.

The fragmentation patterns of butyltin compounds (mono-, di-, and tributyltin) in an electron impact ion source were studied using an isotope pattern reconstruction algorithm with emphasis on isotope ratio measurements from molecular clusters. For this purpose, standards of natural tin isotope abundance and a (119)Sn-enriched mixture of the three compounds were both ethylated and propylated using sodium tetraalkylborates. The corresponding mass spectra of the various tetraalkyltin compounds prepared were obtained by GC/MS after their extraction with hexane. The results showed that pure interference-free molecular clusters were obtained only for certain R(3)Sn(+) ions where no isobaric overlap with R(2)SnH(+) ions occurred (e.g. BuEt(2)Sn(+) overlaps with Bu(2)SnH(+)). These ions are ideal candidates for accurate Sn isotope ratio measurements, while isotope pattern perturbing interferences are observed for other molecular fragments down to Sn(.)(+). Isotope pattern reconstruction algorithm thus can be used as an analytical tool to ensure the absence of molecular interferences--a requirement for accurate isotope ratio measurements from molecular clusters. The relevance of these studies for the determination of butyltin compounds in environmental samples by isotope dilution GC/MS is also discussed.

Environmental Monitoring↗
PubMed2005

Informatics and mass spectrometry challenge.

For the first time this year, we would like to invite you to participate in the Analytical Challenge, which is a series of puzzles to entertain and challenge our readers. We hope that you not only find this feature stimulating but that it provides you with points of further interest for your work and study. And please note: there is a prize to be won (a Springer book from our catalogue up to a value of 75 Euros).These Analytical Challenges are published every two months. Two years ago, we first began with a series of spectroscopy challenges by Ernö Pretsch and Renato Zenobi, which may still be viewed on the 'Springer' chemistry website www.springeronline.com. Mass spectrometry is the topic in the present challenge. Please read on...

Journal Article↗
PubMed2004

Selenium and sulfur trichalcogenides from the chalcogenide exchange reaction.

Various selenium- and sulfur-containing volatiles have been detected and characterized as products of chalcogen exchange reactions. The formation of all possible selenium- and sulfur-containing trichalcogenide isomers (-SeSS-, -SSeS-, -SeSeS-, -SeSSe- and -SeSeSe-) was observed at room temperature in the solutions containing diselenide and trisulfide. Because of the low activation barrier of the selenium exchange reaction, these species are expected also to form in biological systems in the presence of diselenides and higher sulfides. Methyl and ethyl derivatives of these species were characterized using gas chromatography coupled to time-of-flight mass spectrometry with electron impact, chemical, and field ionization. Rearrangements of triselenides lead also to the formation of isomeric branched-structure triselenides, selanadiselenides. Because of the very similar structural properties, the behavior of these novel species was studied under various ionization modes (EI+, CI+, EI-, and CI-).

Chalcones↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

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↗