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Juris Meija

Publications and source records attributed to Juris Meija.

At least 19 recordsLinked to original sources
PubMed2006

Mass spectrometric separation and quantitation of overlapping isotopologues. H2O/HOD/D2O and H2Se/HDSe/D2Se mixtures.

Three conceptually different mathematical methods are presented for accurate mass spectrometric determination of H2O/HOD/D2O and H2Se/HDSe/D2Se concentrations from mixtures. These are alternating least-squares, weighted two-band target entropy minimization, and a statistical mass balance model. The otherwise nonmeasurable mass spectra of partially deuterated isotopologues (HOD and HDSe) are mathematically constructed. Any recorded isotopologue mixture mass spectra are then deconvoluted by least-squares into their components. This approach is used to study the H2O/D2O exchange reaction, and is externally validated gravimetrically. The H2O/D2O exchange equilibrium constant is also measured from the deconvoluted 70 eV electron impact GC/MS data (K = 3.85 +/- 0.03).

Algorithms↗
PubMed2006

Mathematical tools in analytical mass spectrometry.

Over the last few decades, mass spectrometry has become a powerful tool for exploring various aspects of molecular processes occurring in biological systems. Such exploration is leading to a greater understanding of various complex life processes; unraveling these processes poses the greatest challenge to contemporary bioscience. With due respect to sample preparation, data analysis is rapidly becoming a major obstacle to the conversion of experimental knowledge into valid conclusions. It is interesting to note that many problems related to mass spectrometry can be solved using techniques from computer science, graph theory and discrete mathematics. The aim of this manuscript is to recollect several essays that demonstrate the power and the need to apply such skills to mass spectrometry data interpretation. Special attention is paid to situations where traditional chemical analysis reaches its limits but mathematical reasoning can still allow us to reach valid conclusions.

Journal Article↗
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

Investigation of selenium-containing root exudates of Brassica juncea using HPLC-ICP-MS and ESI-qTOF-MS.

Selenium-containing root exudates were investigated in a known selenium accumulator model plant. Indian mustard (Brassica juncea) plants were grown hydroponically and supplemented with selenite (SeO(3)(2-)) in a 25% Hoagland's nutrient solution. Additive concentrations were 0, 1, 5 and 20 microg mL(-1) Se with five replicate plants per treatment level. Plants were exposed to the respective Se solutions for two weeks, then placed in deionized water for two more weeks. The hydroponic solutions were collected for analysis after the first two weeks of selenium supplementation (day 14) and twice during the deionized water period (days 21 and 28). Separation by ion-pairing high performance liquid chromatography was followed by inductively coupled plasma-mass spectrometry (ICP-MS) for selenium specific detection. Chromatographic peaks unable to be identified by retention-time matching were collected for analysis by electrospray ionization mass spectrometry (ESI-MS). Additional chemical experiments were performed for structural elucidation. Several selenium-containing compounds were identified in the exudate-containing solution and two were identified as selenocystine and the selenosulfate (SSeO(3)(2-)) ion. The presence of dimethylselenide (CH(3)SeCH(3)) is also observed but cannot be attributed exclusively to plant exudation because plants were not grown in sterile conditions. Further, the incorporation of fortified selenoamino acids into peptide structures was found to occur under neutral pH conditions, suggesting that exuded enzymes might facilitate such a reaction. Finally, physiological differences resulting from selenium supplementations were noted and discussed.

Chromatography, High Pressure Liquid↗
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↗