Search results for " ionization"
showing 10 items of 621 documents
Thermal degradation of novolac resins by pyrolysis-gas chromatography with a movable reaction zone
1999
Abstract A previously described, a pyrolysis device with a movable reaction zone was used in the present work for thermal degradation of novolac resins. The products of thermal reactions were analysed by pyrolysis–GC. Owing to the heating of reaction zone to the maximal temperature of the chromatographic column, the high boiling pyrolysis products could be analysed. Bisphenols and trisphenols with aromatic rings coupled by methylene bridges and its methyl derivatives have been found among the compounds. The structure of the heavy pyrolysis products has been confirmed using GC–MS.
Lipid hydroperoxides determination in milk‐based infant formulae by gas chromatography
2003
A simple gas chromatograph using a flame ionization detector and a polar capillary column method is proposed for determining hydroperoxides in the lipid fraction of milkbased infant formulas. Tricosanoic acid is used as internal standard. The method includes the following steps: a) the extraction of fat with chloroform/methanol (2:1, v/v), b) the reduction of hydroperoxide acids to hydroxide acids with hydrogen gas and palladium as a catalyst, c) the transmethylation to obtain the methyl esters with acetyl chloride and methanol/ hexane (4:1, v/v), and d) an acetylation with acetic anhydride/ pyridine (4:1, v/v) to obtain an acetoxy derivate of the hydroxide present. Two chromatography runs,…
Determination of triazines and organophosphorus pesticides in water samples using solid-phase extraction.
1991
Abstract Octadecyl (C 18 )-bonded porous silica was evaluated for the extraction of triazine and organophosphorus pesticides from natural water. The extraction results showed an effective performance when 1 l of water was passed through small glass columns containing 500 mg of 50–100-μm C 18 bonded porous silica. The absorbed compounds were removed with ethyl acetate, evaporated to 200 μl and determined by gas chromatography. The overall average recoveries were greater than 85% except for dimethoate and trichlorfon. Application of this procedure to the analysis of natural water samples gave results that agree well with those obtained by solvent extraction methods.
An electrospray ionization mass spectrometric study of the extracellular hemoglobins from Chironomus thummi thummi.
1998
The aquatic larvae of the dipteran, Chironomus thummi thummi contain extracellular hemoglobins which exhibit stage-specific expression. We have used maximum entropy-based deconvolution of the complex, multiply charged electrospray ionization mass spectra, to demonstrate the presence of more than 20 components, ranging in mass from 14,417.3 Da to 17,356.5 Da in the 4th instar larvae. Of the 15 major peaks with intensities > 10 relative to 100 for the 14,417.3 Da-component (CTT-IV), only the 15,528.2-Da peak does not correspond to a known amino acid sequence. Since the number of C. thummi thummi globin genes now stands at 27, including one cDNA and not counting three that must encode known gl…
Method development for the determination of 1,1-dimethylhydrazine by the high-performance liquid chromatography-mass spectrometry technique.
2018
Unsymmetrical dimethyl hydrazine is highly toxic, carcinogenic compound, widely used for organic synthesis and drug development. Therefore, due to its high reactivity, direct analysis is problematic. Current study proposes to use derivatization reaction to increase selectivity and sensitivity of high-performance liquid chromatography–mass spectrometry method. Different derivatization agents were tested and optimal reaction media was found. Derivatization was performed by using small amounts of reagents to lower the cost of analysis. The full validation of the method was performed and it can be used in a routine control in pharmaceutical analysis. Method sensitivity is 0.15 ppm, and lineari…
Chromium(VI) oxide oxidation of non-ethoxylated and ethoxylated alcohols for determination by electrospray ionization mass spectrometry
2010
A new derivatization procedure to increase the sensitivity of electrospray ionization mass spectrometry (ESI-MS) to non-ethoxylated and ethoxylated alcohols was investigated. The analytes were oxidized with chromium(VI) oxide and the resulting carboxylic and ethoxy-carboxylic acids were isolated by extraction with ethyl acetate; the extracts were alkalinized and infused into the ESI-MS system working in the negative-ion mode. The yields of the combined oxidation-extraction were ca. 100% for non-ethoxylated fatty alcohols dissolved in acetone and they decreased moderately in samples containing increasing amounts of water (e.g., a 75% yield was obtained with 50% water). Ethoxylated alcohols w…
Analysis of neuropeptide Y and its metabolites by high-performance liquid chromatography-electrospray ionization mass spectrometry and integrated sam…
2000
A novel restricted access cation exchanger with sulphonic acid groups at the internal surface was proven to be highly suitable in the sample clean up of peptides on-line coupled to HPLC-electrospray ionization (ESI)-MS. Neuropeptide Y (NPY) and several of its fragments in plasma were subjected to the sample clean-up procedure. The peptides were eluted by a step gradient from the restricted access column, applying 10 mM phosphate buffer pH 3.5 from 5 to 20% (v/v) of acetonitrile with 1 M NaCl and transferred to a Micra ODS II column (33x4.6 mm). The separation of the peptides and their fragments was performed by a linear gradient from 20 to 60% (v/v) acetonitrile in water with 0.1% formic ac…
Determination of several aminoglycoside and macrolide antibiotics in animal tissues by liquid chromatography-electrospray ionization-tandem mass spec…
2008
Simultaneous determination of imidacloprid, carbendazim, methiocarb and hexythiazox in peaches and nectarines by liquid chromatography–mass spectrome…
2002
Abstract A liquid chromatographic (LC) atmospheric pressure chemical ionization mass spectrometric (MS) method is described for determining imidacloprid, carbendazim, methiocarb and hexythiazox in peaches and nectarines. The samples were extracted with ethyl acetate and anhydrous sodium sulfate. Recoveries yield for spiking samples were ranged from 64±9% (R.S.D) for carbendazim to 108±14% (R.S.D.) for hexythiazox at the concentration of 0.1 mg kg−1 (n=5). The correlation coefficients were greater than 0.998 over the range between 0.02 and 2 mg kg−1. The limits of quantitation (LOQ) were 0.02 mg kg−1 for all the pesticides. The applicability of the method to detect and quantify imidacloprid,…