1,721,065 research outputs found
Analysis of tomato glycoalkaloids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry.
Full text linkSteroidal glycoalkaloids (SGAs) extracted from tomato leaves and berries (Lycopersicon esculentum Mill.) were separated and identified using optimized reversed-phase liquid chromatography with electrospray ionization (ESI) and ion trap mass spectrometry (ITMS). The ESI source polarity and chromatographic conditions were evaluated. The ESI spectra contain valuable information, which
includes the mass of SGAs, the mass of the aglycones, and several characteristic fragment ions. Cleavage at the interglycosidic bonds proximal to the aglycones is the most prominent process
in the ESI process. A protonated molecule, [M+H]+, accompanied by a mixed adduct ion, [M+H+Na]2+, was observed for a-tomatine (i.e., m/z 1034.7 and 528.9) and dehydrotomatine (i.e., m/z 1032.6 and 527.9) in positive ion mode spectra. The structures of these tomato glycoalkaloids were confirmed using tandem mass spectrometry. The identification of a new a-tomatine isomer
glycoalkaloid, named filotomatine (MW 1033), which shares a common tetrasaccharide structure (i.e., lycotretraose) with a-tomatine and dehydrotomatine, and soladulcidine as an aglycone, is described for the first time. It occurs in significant amounts in the extracts of wild tomato foliage. Multistage mass spectrometry both of the protonated molecules and of the doubly charged ions was used for detailed structural elucidation of SGAs. Key fragmentations and regularities in fragmentation pathways are described and the fragmentation mechanisms involved are propose
Riboflavin in dietary sources: separation and detection by CE-LIF
No full textThis article demonstrates the suitability of capillary electrophoresis coupled to laser-induced fluorescence detection for riboflavin determination in common foods and beverages
STUDY OF SUGAR ACIDS SEPARATIONS BY HIGH-PERFORMANCE ANION-EXCHANGE CHROMATOGRAPHY-PULSED AMPEROMETRIC DETECTION USING ALKALINE ELUENTS SPIKED WITH Ba2+, Sr2+, Ca2+ AS ACETATE OR NITRATE SALTS.
No full textThe influence of Ba2+, Ca2+ and Sr2+ ions on the anion-exchange chromatographic separation of some carboxylated sugar acids such as D-gluconic acid, N-acetylneuraminic acid, muramic acid and D-galacturonic, D-mannuronic and D-glucuronic acids was investigated. The chromatographic technique was coupled with pulsed amperometric detection using gold ar a working electrode. Since acidic carbohydrates are strongly retained on the anion-exchange column, acetate and nitrate as counterions were used to regulate retention within 30 min. The addition of alkaline-earth metal ions at a millimolar concentration to the alkaline eluents does impart a noticeable decrease in the retention, especially for N-acetylneuraminic and uronic acids. Complexation of these compounds with free divalent metal ions presumably occurs in the alkaline eluent. The extent of decreased retention is related to each divalent metal ion, and a good correlation was found between the retention modulus (eta = k'/k(o)') and the stability constant of each sugar-metal ion complex. As expected, calcium ion induced a slightly greater retention compared to strontium and barium ions, and this is consistent with the fact that alduronate-calcium complexes are relatively more stable (eta < 1.00). We demonstrate also that upon the addition of Ba2+ and Sr2+ ions in the alkaline eluent, but the same cannot be claimed for calcium-containing eluents, there is a gain in sensitivity for all compounds investigated. The increment on the peak height when the column was eluted with NaOH spiked with Ba(NO3)(2) was generally higher (5-75%) than that with Ba(OAc)(2)
Scrambling of autoinducing precursor peptides investigated by infrared multiphoton dissociation with electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry
No full textTwo synthetic precursor peptides, H2N-CVGIW and H 2N-LVMCCVGIW, involved in the quorum sensing of Lactobacillus plantarum WCFS1, were characterized by mass spectrometry (MS) with electrospray ionization and 7-T Fourier transform ion cyclotron resonance (ESI-FTICR) instrument. Cell-free bacterial supernatant solutions were analyzed by reversed-phase liquid chromatography with ESI-FTICR MS to verify the occurrence of both pentapeptide and nonapeptide in the bacterial broth. The structural characterization of both protonated peptides was performed by infrared multiphoton dissociation using a continuous CO2 laser source at a wavelength of 10.6 μm. As their fragmentation behavior cannot be directly derived from the primary peptide structure, all anomalous fragments were interpreted as neutral loss of amino acids from the interior of both peptides, i.e., loss of V, G, VG and M, MC, V, CC, from H2N-CVGIW and H 2N-LVMCCVGIW, respectively. Mechanisms of this scrambling are proposed. FTICR MS provides accurate masses of all fragment ions with very low absolute mass errors (<1.6 ppm), which facilitated the reliable assignment of their elemental compositions. The resolving power was more than sufficient to resolve closely isobaric product ions with routine subparts per million mass accuracies. Only the occurrence of pentapeptide was found in the cell-free culture of L. plantarum, grown in Waymouth's medium broth, with a low content of 5.2 ± 2.6 μM by external calibration. Most of it was present as oxidized H2N-CVGIW, that is, the soluble disulfide pentapeptide with a level tenfold higher (i.e., 50 ± 4 μM, n = 3)
Direct electrical communication of cytochrome c and cytochrome b5 at basal plane graphite electrodes modified with lauric acid or laurylamine
No full textDetermination of Proline and Free Monosaccharides in Wine Samples by High-pH Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD)
No full textA sensitive and selective analytical method for the simultaneous separation and quantitative determination of proline and free monosaccharides in wine samples by high-performance anion-exchange
chromatography coupled with pulsed amperometric detection is described. Under optimized experimental conditions, a complete separation was obtained in less than 30 min, using an isocratic elution with 10 mM NaOH and 1 mM Ba(OAc)2. No postcolumn addition of strong bases to the eluent for enhancing detection sensitivity was needed. Upon 25-fold sample dilution and purification to avoid interference of tannins, pigments, and phenolic compounds, the fingerprinting of common monosaccharides (i.e., arabinose, glucose, fructose, galactose, and xylose) and proline in wines, musts, and vinegars can be easily accomplished. The method allows high recovery and satisfies the necessary requirements for accuracy, repeatability, and sensitivity. Values obtained for proline content ranged from 470 to 1190 mg/L in “Aglianico” red wines (mean value, 870 ( 192 mg/L, n ) 21) and from 168 to 286 mg/L in white wines (mean value, 208 ( 32 mg/L, n ) 11). Lower levels were found in musts of red and white grapes, 550 and 87 mg/L, respectively. The lowest content of proline, ca. 10 mg/L, was found both in white and red vinegars
Acylated glucosinolates with diverse acyl groups investigated by high resolution mass spectrometry and infrared multiphoton dissociation
No full textQuantitative Determination of Taurine in Real Samples by High-Performance Anion-Exchange Chromatography with Pulsed Electrochemical Detection
No full textAs taurine is a very important compound involved in a large number of metabolic processes, it is naturally present in the mammal tissues and is often deliberately added in some foods as a fortifying component. A detailed knowledge of taurine metabolic roles in biological systems can be obtained only if a sensitive, reliable and rapid analytical method is available. This article describes the successful application of high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) for taurine determination in egg white and yolk samples, as well extracts of human serum and urine. Applications are shown for determination of taurine in soft drinks and pharmaceutical preparations where the taurine content was evaluated by standard additions. These results were achieved without prior derivatization of taurine
ELECTROCATALYSIS AND AMPEROMETRIC DETECTION OF ALDITOLS AND SUGARS AT A GOLD-NICKEL COMPOSITE ELECTRODE IN ANION-EXCHANGE CHROMATOGRAPHY.
No full textA novel Au-Ni composite electrode prepared by cathodic precipitation/deposition of nickel hydroxide on the gold surface was characterised. The resulting composite electrode was evaluated as an amperometric sensor in flow injection analysis and anion-exchange chromatography for the quantitation of alditols and simple carbohydrates. Constant potential detection at +0.6V vs Ag/AgCl and a pulsed detection mode were employed, and their applicability and usefulness discussed. The detection Limits (S/N = 3) for all investigated compounds, in both modes of detection, ranged between 1.5 and 7.5 pmol injected. Linear dynamic ranges spanned over four and three orders of magnitude when the composite electrode was used in the DC or pulsed mode. The main advantage of the Au-Ni composite electrode is that detection selectivity can be tailored by the choice of the detection mode and by the polarisation potential. As an example, we show how to detect common carbohydrates in tea powder using the constant potential detection mode
METHOD DEVELOPMENT FOR THE QUANTITATIVE DETERMINATION OF LACTULOSE IN HEAT.TREATED MILKS BH HPAEC WITH PULSED AMPEROMETRIC DETECTION
No full textA robust, rapid, and sensitive high-performance anionexchange
chromatographic method for the separation and quantitative determination of lactulose in heated milks, along with other common milk carbohydrates, has been developed. Complete separation of galactose, glucose, N-acetylgalactosamine, lactose, lactulose, and epilactose was isocratically accomplished in about 22 min by an anion-exchange column eluted with 10 mM NaOH spiked
with 2 mM Ba(OAc)2. The within-day repeatability was lower than 2.1% for 10 repetitive injections. Under optimized conditions, there was no need either of postcolumn addition of strong bases to the eluent for enhancing detection sensitivity or, even more important, for column regeneration between chromatographic runs.
Upon 100-fold sample dilution, the amperometric response
of lactulose in milk samples was found to be linear up to 100 microM (r ) 0.99935) with a limit of detection equal to 1.2 microM (S/N = 3). The lactulose content in ultrahigh-temperature (UHT) and sterilized milks was evaluated by a calibration graph using 2-deoxyglucose as the internal standard, making the proposed method very useful in discriminating among heat-treated milks. Whereas the mean value of lactulose in skimmed, partially skimmed, and whole UHT milks ranged from 10 to 90 mg/100 mL,
lactulose content in bottle-sterilized whole milk (two samples) was higher than 140 mg/100 mL. The presence of epilactose, which is another isomer of lactose, was also ascertained in sterilized milk
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