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Jorge Ruiz Encinar

Publications and source records attributed to Jorge Ruiz Encinar.

18 recordsLinked to original sources
PubMed2006

Identification of selenium species in selenium-enriched Lens esculenta plants by using two-dimensional liquid chromatography-inductively coupled plasma mass spectrometry and [77Se]selenomethionine selenium oxide spikes.

Selenium speciation in Se-enriched Lens esculenta grown in hydroponic culture containing inorganic selenium as Na(2)SeO(3) and Na(2)SeO(4) was performed. After 16 days of growth, the plants were collected and divided in two parts, roots and stems and then analysed to identify and quantify selenium species. Speciation studies of the enzymatic extracts were carried out by using anion-exchange (PRP-X100) and size-exclusion/ion-exchange (Shodex Asahipak) columns coupled to inductively coupled plasma mass spectrometry (ICP-MS). The need of using two independent chromatographic mechanisms for unambiguous species identification is demonstrated. Moreover, the use of a [(77)Se]selenomethionine selenium oxide spike turned out to be critical to discriminate between selenium selenomethioine selenium oxide and selenocysteine.

Chromatography, Liquid↗
PubMed2006

Fractionation of selenium-containing proteins in serum by multiaffinity liquid chromatography before size-exclusion chromatography-ICPMS.

Immunoaffinity chromatography has been investigated for fractionation of serum into selenoalbumin and true selenoproteins. Among several albumin-depletion kits tested, a multiaffinity column specifically binding albumin and five other major serum proteins provided the best results. It extracted ca 95% of both albumin and selenoalbumin, which enabled interference-free determination of glutathione peroxidase, selenoprotein P, and selenoalbumin by size-exclusion chromatography combined with inductively coupled plasma mass spectrometry (SEC-ICPMS). The efficiency of the multiaffinity column did not vary over a period of 18 months. The purity of fractions separated by immunoaffinity LC was confirmed by elution-volume matching with standards in SEC-ICPMS and by selenopeptide mapping in capillary HPLC-ICPMS. Quantification of the selenium distribution among the different proteins in human serum from a control group and from a person on a selenium-rich diet revealed that 67% of the supplemented selenium was incorporated into albumin, 30% into glutathione peroxidase, and 3% into selenoprotein P.

Albumins↗
PubMed2006

Selenium bioaccessibility assessment in selenized yeast after "in vitro" gastrointestinal digestion using two-dimensional chromatography and mass spectrometry.

In order to investigate the potentially bioavailable selenium-containing compounds in the selenized yeast candidate reference material SEAS 6, a two-dimensional (size exclusion-reversed phase) chromatography approach has been worked out. Electrospray tandem mass spectrometry (ESI Q-TOF MS) was then used for off-line identification of low molecular weigh selenocompounds generated during the gastrointestinal digestion. Selenomethionine (SeMet) was the major compound identified in the gastrointestinal extract while SeMet selenoxide was its main degradation product formed after medium and long-term sample storage, respectively. Total Se and SeMet were quantified in both the soluble extracts and the residue. Results showed that 89+/-3% of total Se was extracted after gastrointestinal digestion, but only 34+/-1% was surprisingly quantified as free SeMet. The rest of Se was present as many other low, medium and high molecular weight Se-species, which could be detected and further characterized by using the two-dimensional chromatography approach proposed here. Interestingly, most of Se-species seemed to be Se-peptides unspecifically produced by the gastrointestinal juice. These results show for the first time that while the efficiency of human gastrointestinal digestion to dissolve Se-containing proteins present in yeast may be high, its efficiency to convert them into free SeMet is much lower. Se-species present in the insoluble residue (not assimilated by the organism), accounting for 11+/-1% of the total Se in selenized yeast, were also studied. After treatment with SDS (denaturing agent) only 13+/-2% of this "insoluble" Se was solubilized, indicating that it was mainly non-protein bound and likely associated to other insoluble matrix components.

Chromatography, High Pressure Liquid↗
PubMed2005

Analysis of the selenium species distribution in cow blood by size exclusion liquid chromatography-inductively coupled plasma collision cell mass spectrometry (SEC-ICPccMS).

A method for performing rapid semiquantitative screening of the distribution of Se species in the blood of cows fed with a diet enriched in selenized yeast was optimized. The method was based on direct injection of a blood sample onto a high resolution size exclusion chromatographic column and fractionation of the selenium species. Selenium was detected on-line by ICP-MS with a collision cell. The concentrations of selenized haemoglobin and free selenomethionine were estimated using the chromatogram. The method was applied to a study involving 15 control and 15 treated dairy cows at four different supplementation time points. The increase in the selenomethionine and selenized haemoglobin was a linear function of the total selenium concentration. A threshold value of 600 ng ml(-1) of total Se was established beyond which selenomethionine could not be incorporated into the protein. No inorganic selenium was found to be present. The total selenium in cow blood correlated well with that in milk. The selenium supplementation did not change the protein distribution profiles for other essential elements (Cu, Fe, Mn, Zn).

Animals↗
PubMed2005

Investigation of the recovery of selenomethionine from selenized yeast by two-dimensional LC-ICP MS.

Determination of selenomethionine in selenized yeast by HPLC-ICP MS has been revisited with the focus on recovery of this amino acid during the proteolytic digestion and chromatography steps. Recovery of the extracted selenium from an anion-exchange column was 100% but selenomethionine quantified by the method of standard additions accounted only for 67% of the selenium injected. Analysis (by size-exclusion LC-ICP MS) of the eluate collected before and after the selenomethionine peak showed the presence of oxidized selenomethionine (ca. 3%) and selenomethionine likely to be unspecifically associated with the biological matrix continuum (ca. 11%). This finding was validated by two-dimensional LC-ICP MS using a different elution order, i.e. size-exclusion anion-exchange. The approach developed enabled demonstration that more than 80% of selenium in the selenized yeast is actually present in the form of selenomethionine and suggests that many results reported elsewhere for the concentration of this vital amino acid in selenized yeast may be negatively biased. The research also provided insight into speciation of selenium in the solid residue after proteolytic extraction but the additional amount of selenomethionine recovered was negligible (<1.5%).

Anion Exchange Resins↗
PubMed2004

Determination of selenomethionine and selenocysteine in human serum using speciated isotope dilution-capillary HPLC-inductively coupled plasma collision cell mass spectrometry.

A method for the accurate determination of selenoamino acids in human serum by HPLC-ICPMS was developed using the species-specific isotope dilution analysis principle. A serum sample was enzymatically digested with a mixture of lipase and protease after derivatization of the selenocysteine residues with iodoacetamide. The selenoamino acid fraction was isolated by size exclusion LC followed by the separation of selenomethionine and the carboxymethylated selenocysteine by capillary HPLC. The isotope-specific determination of 77Se and 80Se was achieved on-line by ICP collision cell MS allowing the removal of polyatomic interferences. Quantification was carried out by isotope dilution using a 77Se-labeled selenomethionine spike and the determination of the 77Se/80Se ratio in the cHPLC selenomethionine peak. The accurately determined selenomethionine was used as an internal standard for the selenocysteine determination from the same chromatogram. The modification of the previously developed cHPLC-ICPMS interface allowed the reduction of the absolute detection limits twice (down to the 75-fg level), which resulted in the lowest ever reported procedural detection limits (below 0.5 ng g(-1) for a 450-mg serum sample). The precision was less than 5% RSD. The method was validated by the mass balance of selenium (amino acid incorporated vs total).

Chromatography, Gel↗
PubMed2004

Monitoring the degradation and solubilisation of butyltin compounds during in vitro gastrointestinal digestion using "triple spike" isotope dilution GC-ICP-MS.

An in vitro gastrointestinal digestion approach in combination with species-specific isotope dilution analysis has been employed for the first time to study the transformation reactions as well as the solubilisation of butyltin species throughout a simulated human digestion. Different sample preparation procedures were assayed in order to avoid problems derived from lack of isotope equilibration between the endogenous and the isotopically-enriched added species. A "triple spike" approach, which can be used to calculate the corrected concentrations of mono-, di-, and tributyltin (MBT, DBT and TBT, respectively), as well as six interconversions, was employed throughout this work. In order to calculate and compare the species degradation factors, a triple spike solution containing each butyltin species enriched in a different isotope was added to the simulated gastric and intestinal fluids before the digestion procedures in the presence and in the absence of a solid biological matrix (commercial mussel tissue). Additionally, by analysing the soluble and insoluble fractions resulting from the simulated digestion of a commercial mussel tissue (gastric and gastric plus intestinal digestion), total mass balances for each butyltin compound could be derived. For this purpose, the isotopically-enriched species were added after the enzymatic digestions in order to avoid problems derived from lack of isotope equilibration. The mass balances provided information not only about the solubilisation but also about the degradation of the butyltin species during the digestion procedures. Good agreement between the degradation factors calculated under all experiments performed in this work and between those reported in previous works were obtained. The most serious degradation observed was that of DBT to produce MBT, whereas slight degradations of TBT and MBT were detected. Moreover, a worrying 61% of the original total butyltin content present in a commercial mussel tissue was found to be solubilised after complete simulated gastrointestinal digestion, with minimal degradation of TBT.

Gas Chromatography-Mass Spectrometry↗
PubMed2004

Identification of non-peptide species in selenized yeast by MALDI mass spectrometry using post-source decay and orthogonal Q-TOF detection.

The potential of tandem mass spectrometry following matrix-assisted laser desorption ionization (MALDI) was studied for speciation of selenium. Non-peptide selenium-containing compounds were isolated from a selenized yeast aqueous extract by size-exclusion chromatography. Post-source decay (PSD) was compared with orthogonal quadrupole collision cell dissociation for the purpose of obtaining fragmentation and structural information. In the PSD mode, the use of ion gate covering the whole isotopic cluster of the parent compound allowed the immediate recognition of fragments containing Se and those in which this element was absent. The tandem mass spectra obtained by orthogonal MALDI Q-TOF were equally informative in terms of the number of fragments but suffered from a poorer sensitivity. The mass accuracy was ca. 20 times better in the oMALDI configuration than in the PSD mode. An unknown selenium compound with an m/z 388 was detected with a mass accuracy of 3 ppm according to the proposed empiric formula.

Selenium↗
PubMed2004

Speciation of selenium in selenium-enriched shiitake mushroom, Lentinula edodes.

The major selenium compound in an aqueous extract of the most popular mushroom in Eastern Asian countries, shiitake ( Lentinula edodes), fortified with selenium (Se) was identified by means of hyphenated techniques, i.e. HPLC-inductively coupled argon plasma mass spectrometry and HPLC-electrospray ionization mass spectrometry (HPLC-ICP MS and HPLC-ESI MS). Sixty-eight per cent of the total Se in the selenized shiitake was extracted with water, and 49.8% of the Se in the water extract was eluted in the high molecular mass fraction (>40,000 kDa) before incubation at 37 degrees C. After incubation, 40.6% of the Se in the water extract was eluted in a lower molecular mass fraction and the Se eluted in the high molecular mass fraction had decreased to 14.0%, suggesting that the major selenium compound in the water extract was initially in a form bound to macromolecule(s) and was then enzymatically liberated from the macromolecule(s). The retention time of the liberated selenium compound in HPLC-ICP MS matched that of selenomethionine (SeMet), and the masses of molecular and fragment ions detected by HPLC-ESI MS also suggested that the selenium compound was SeMet. The selenized shiitake accumulated Se as SeMet, and SeMet might be bound to the water extractable high molecular mass protein(s).

Chromatography, High Pressure Liquid↗
PubMed2003

Development of a sheathless interface between reversed-phase capillary HPLC and ICPMS via a microflow total consumption nebulizer for selenopeptide mapping.

A sheathless interface based on a total consumption micronebulizer operating at flow rates in the range 0.5-7.5 microL min(-1) was developed between capillary HPLC and ICPMS. It allowed the efficient nebulization and transport into the plasma of mobile phases containing up to 100% organic solvent without either cooling the spray chamber or oxygen addition. The coupled system was applied to selenopeptide mapping in a protein fraction isolated from a selenized yeast extract. The detection limits were 150 (80Se) and 200 fg (82Se) for a quadrupole instrument with and without a collision cell, respectively, which is a factor 100-150 less than that reported elsewhere for HPLC-ICPMS. The minimal peak broadening ( approximately 5 s at the half-height) allowed baseline resolution of a mixture containing more than 30 selenopeptides, many of which could not be separated using the conventional HPLC-ICPMS coupling.

Chromatography, High Pressure Liquid↗
PubMed2003

Identification of water-soluble selenium-containing proteins in selenized yeast by size-exclusion-reversed-phase HPLC/ICPMS followed by MALDI-TOF and electrospray Q-TOF mass spectrometry.

An approach to speciation of selenium incorporated in yeast proteins was developed. The tryptic digest of a water-soluble protein fraction isolated by size-exclusion chromatography was analyzed by reversed-phase HPLC/ICPMS. The selenopeptides selected owing to the detector's elemental specificity were then analyzed by MALDI-TOFMS in order to select target ions for collision-induced dissociation MS. The latter, carried out with an electrospray Q-TOF spectrometer, enabled the sequencing of the selenopeptides detected by HPLC/ICPMS. The approach allowed for the first time the identification of a family of Se-containing proteins resulting from the replacement by selenomethionine of 2-9 methionine residues in a salt-stress-induced protein SIP18 (Mr 8874). The presence of these proteins was confirmed by MALDI-TOFMS of the original (nondigested) protein fraction. Another selenium protein identified was a heat-shock protein HSP12 (Mr 11693) in which the only methionine residue was replaced by selenomethionine. These two Se-containing proteins accounted for more than 95% of selenium in the water-soluble protein fraction.

Amino Acid Sequence↗
PubMed2003

Detection of selenocompounds in a tryptic digest of yeast selenoprotein by MALDI time-of-flight MS prior to their structural analysis by electrospray ionization triple quadrupole MS.

MALDI-TOFMS was proposed as a key technique to a novel generic approach for the speciation analysis of selenium in yeast supplements. Owing to a lower detection limit and superior matrix tolerance to electrospray MS it allowed a successful detection of selenocompounds in samples for which electrospray MS had failed. The analytical approach developed was applied to the identification of a previously unreported selenopentapeptide (m/z 596) in the tryptic digest of a water-soluble selenoprotein fraction isolated by size-exclusion chromatography. The information on the mass of the protonated molecular ion obtained from MALDI allowed the optimization of the conditions for collision induced dissociation MS using a triple quadrupole spectrometer that enabled the determination of the amino acid sequence SeMet-Asn-Ala-Gly-Arg of the selenopeptide.

Dietary Supplements↗
PubMed2003

Isotope dilution analysis as a definitive tool for the speciation of organotin compounds.

Different spike solutions available for the determination of butyltin compounds by isotope dilution analysis are described and applied for the determination of butyltin compounds in PACS-2 certified reference material. Additionally, those spike solutions were evaluated during the course of an interlaboratory exercise organised by the National Research Council of Canada and the Laboratory of the Government Chemist (UK) in order to quantify tributyltin in a pilot sediment. The aim of this project was to evaluate the capabilities of isotope dilution mass spectrometry to reduce the uncertainty in the certification of Reference Materials for the speciation of organotin compounds. All participants were supplied with a 17Sn-enriched TBT solution from the Laboratory of the Government Chemist (UK). In our case, we performed the analysis of the pilot sediment also using a 119Sn enriched spike (mixed mono-, di- and tributyltin) and a 118Sn-119Sn double spike. The use of these additional spike solutions not only allowed the determination of monobutyltin and dibutyltin in the pilot sediment but also the evaluation and correction of possible extraction-derived rearrangement reactions. An excellent agreement amongst our results and between the participants was obtained with a precision of 8.4% RSD at a level of ca. 80 ng TBT g(-1) (as Sn).

Journal Article↗
PubMed2002

Evaluation of accelerated solvent extraction for butyltin speciation in PACS-2 CRM using double-spike isotope dilution-GC/ICPMS.

Pressurized liquid extraction using the accelerated solvent extractor (Dionex ASE 200) has been evaluated for the determination of mono-, di- and tributyltin (MBT, DBT, and TBT, respectively) in PACS-2 certified reference material. A double-enriched spike containing 119Sn-enriched MBT and TBT and 118Sn-enriched DBT allowed for the simultaneous determination of the three butyltin species and the factors governing species interconversion. The stability of the spike was evaluated by reverse isotope dilution experiments covering more than one year with satisfactory results. Quantitative recoveries using ASE for TBT and DBT were obtained at temperatures above 110 degrees C. The effect of the extraction time and number of static cycles was evaluated. Results suggest that extraction efficiency was quantitative with extraction times as low as 10 min for all butyltin species at 110 degrees C. Decomposition reactions were only detected at the higher temperatures assayed (140 and 175 degrees C) and that was only for the degradation of DBT to MBT (approximately 4%). The results found for MBT were approximately 25% higher than the certified value for the PACS-2 sediment reference material in agreement with previous results obtained by ultrasonic and microwave assisted extraction.

Environmental Pollutants↗
PubMed2002

Determination of butyltin compounds in environmental samples by isotope-dilution GC-ICP-MS.

Isotope-dilution analysis in combination with GC-ICP-MS detection has been applied to the determination of butyltin species in environmental samples. Different spikes containing the isotopically labeled butyltin species have been synthesized in the laboratory after optimization of the reaction conditions. The isotopic compositions of the tin species in the different spike solutions were determined by GC-ICP-MS after derivatization by aqueous ethylation with sodium tetraethylborate. Reverse isotope-dilution analysis was used for quantitation of the spike solutions by means of natural MBT, DBT, and TBT standards. The mixed spikes were used for simultaneous analysis of MBT, DBT and TBT in the certified reference materials, PACS-2, CRM 462, and CRM 646, with satisfactory results. The excellent agreement of the different speciation results obtained by use of the different spikes is a good indicator of the precision, accuracy, and reliability which can be achieved by using isotope-dilution analysis for trace metal speciation. Application of a double spike containing (119)Sn-enriched MBT (79.7 At%), (118)Sn-enriched DBT (86.7 At%), and (119)Sn-enriched TBT (83.1 At%) also enabled evaluation of the conditions resulting in quantitative extraction of the species from the solid matrix, in combination with possible alterations depending on the different extraction procedures used (mechanical shaking, ultrasounds, and microwaves). Mathematical equations used for this purpose computed the correct species concentrations directly and, additionally, the decomposition factors (from TBT to DBT and from DBT to MBT) after precise measurement of the (119)Sn/(120)Sn and (118)Sn/(120)Sn ratios for all butyltin species by GC-ICP-MS.

Chromatography, High Pressure Liquid↗
PubMed2002

Evaluation of extraction techniques for the determination of butyltin compounds in sediments using isotope dilution-GC/ICPMS with 118Sn and 119Sn-enriched species.

Different liquid-solid extraction techniques, including room-temperature leaching with mechanical shaking, ultrasonic, and microwave-assisted extractions, have been evaluated for the quantitative speciation of tin for mono-, di-, and tributyltin (MBT, DBT, and TBT, respectively) in PACS-2 and BCR-646 certified reference materials. A methanol-acetic acid mixture was used as the extractant reagent in all cases. For this purpose, a mixed spike containing 119Sn-enriched MBT (79.7 At%), 118Sn-enriched DBT (86.7 At%), and 119Sn-enriched TBT (83.1 At%), was synthesized, characterized, and used for isotope dilution analysis. The isotopic composition of the mixed spike was determined by gas chromatography/ICPMS after aqueous ethylation using sodium tetraethylborate, and the determination of the concentration of the different species in the spike was performed by means of reverse isotope-dilution analysis using natural MBT, DBT, and TBT standards. In the analysis of the certified sediments, the sample was spiked with the mixed spike, extracted under different conditions, derivatized with sodium tetraethylborate, and extracted into hexane, and the isotope ratios 120/118 and 120/119 were measured as peak area ratios for all butyltin species after GC/ICPMS. Mass bias was corrected using a derivatized natural standard every three sample injections. Sequential degradation reactions during extraction (from TBT to DBT, from DBT to MBT, and from MBT to inorganic tin) were assumed, and mathematical equations were developed that allowed the determination of the correct species concentration and the decomposition factor for each of the transformation reactions. For ultrasonic extraction and mechanical shaking, negligible degradation reactions were observed. However, for microwave assisted extractions, degradation factors up to 7% (TBT to DBT) and 16% (DBT to MBT) were obtained for both reference materials when high-MW energy was applied in the extraction step. For the three extraction techniques tested, the DBT and TBT concentration values obtained for PACS-2 closely matched the certified values. However, for MBT the concentrations found by microwave and ultrasonic extraction were much higher than the certified value. This was not the case for mechanical shaking. The results obtained for BCR-646 using microwave assisted extraction were in good agreement with the certified values for all tin species.

Environmental Pollutants↗