Electron Impact Mass Spectrometric Analysis Research Articles

Synthesis, characterization, and sorption properties of silica gel-immobilized pyrimidine derivative

5-Benzylidene-2-thiobarbituric acid (BzTBA), a pyrimidine derivative, was used to modify the surface of silica gel–chloropropyltrimethoxysilane (Si-Cl) via chemical immobilization to produce a new pyrimidine silica phase (Si-BzTBA). Identification of the surface modification was characterized and performed on the basis of infrared as well as elemental analysis. Thermal desorption method was found to give 0.129–0.143 mmol g −1 as surface coverage values. Metal sorption properties of Si-BzTBA were also studied and the evaluated results refer to the high metal sorption of Si-BzTBA for copper(II), mercury(II), cadmium(II), and lead(II) with the same order. These four Si-BzTBA–metal complexes were also synthesized and the stoichiometric ratios were identified as 1:1 except lead complex was found to give a 1:2 ratio. Electron impact–mass spectrometric analysis (EI-MS) with 70 eV ionization energy was used as a potential thermal method for the confirmation of surface modification of Si-BzTBA and its metal complexes based on fragmentation elucidation of thermally desorbed ion peaks. The EI-MS of Si-BzTBA was found to show several characteristic fragment ion peaks that are directly related to the chemical binding of BzTBA to SiCl phase. Differential scanning calorimetry study (DSC) was also performed to evaluate the various kinetic and thermodynamic parameters of thermal degradation processes and have been enumerated. The results of EI-MS and DSC are very similar in many respects.

Aspects of surface modification, structure characterization, thermal stability and metal selectivity properties of silica gel phases-immobilized-amine derivatives

Four silica gel phases-bound-amine derivatives (I–IV) were prepared based on chemical immobilization technique. The surface modification was identified by determination of the coverage values in mmol g −1 via thermal desorption method (1.463–1.807) and elemental analysis of nitrogen and carbon contents (1.089–2.456). Structure characterization related to immobilization of the amine derivatives was accomplished and evaluated by means of infrared (IR) and secondary ion mass spectrometric (SIMS) technique. The modified silica gel phases (I–IV) along with their interaction products with copper(II) were also examined by electron impact mass spectrometric analysis (EI-MS) as a method for evaluation of their thermal stability and structure elucidation. Potentiometric titration as a method of characterization was applied for the modified silica gel phases (II–IV) and their copper(II)-adduct. A series of bi- and trivalent metal ions were selected to focus more aspects of the selectivity properties incorporated into the modified silica gel phases for binding and interaction with these metals based on determination of the distribution coefficient and separation factor. The results of these evaluation processes were found to prove higher selectivity and preference of these four phases for binding with lead(II) and cadmium(II) compared to other metal ions.

Characterization of Surface Modification, Thermal Stability, and Metal Selectivity Properties of Silica Gel Phases‐Immobilized Dithiocarbamate Derivatives

Carbon disulphide was used to modify the surface of silica gel phases containing amine moieties for the formation of four phases-immobilized dithiocarbamate derivatives (I–IV). Characterization of the surface modification by the organic modifier was accomplished by several means of instrumental analysis. These include infrared, secondary ion mass spectrometry (SIMS), as well as, thermal desorption analysis for determination of the surface coverage values (1.051–1.501 mmol g−1). The thermal stability and structure characterization of the modified silica gel phases (I–IV), along with their mercury(II) adducts, were studied and evaluated on the basis of electron impact mass spectrometric analysis (EI‐MS). The results of this study proved higher thermal stability characters incorporated into the metal adduct compared to the free silica gel phase. The selectivity properties incorporated into the modified silica gel phases for binding and interaction with a series of bi‐ and trivalent metal ions were studied and evaluated by determination of the distribution coefficient and separation factor. The results of these evaluation processes were found to point out the higher selectivity and preference of these four phases for binding with mercury(II), copper(II), and cadmium(II) compared to other metal ions.

Occurrence and biosynthesis of 11 (R)-hydroxy-eicosatetraenoic acid (11-R-HETE) in the Caribbean soft coralPlexaurella dichotoma

Gorgonian soft corals from the Caribbean Sea are known to contain prostaglandin-like compounds as well as other products of arachidonic acid lipoxygenation, and the formation of the latter has been suggested to represent the first step in prostaglandin biosynthesis. Here we present evidence for the presence of 11-R-hydroxy-5Z, 8Z, 12E, 14Z-eicosatetraenoic acid (11-R-HETE), as well as of the enzyme responsible for its biosynthesis, in the Caribbean gorgonianPlexaurella dichotoma. Lipid extracts fromP. dichotoma were purified by conventional SiO2 column chromatography followed by reversed phase high-pressure liquid chromatography (HPLC). These yielded a component having chromatographic and spectroscopic properties identical to synthetic 11-HETE. Electron impact mass spectrometric analysis of the acetoxy-, methyl ester derivative of the compound confirmed its identity as 11-HETE, while chiral phase HPLC of the methyl ester derivative showed that the stereochemistry of the alcoholic carbon atom wasR. Enzymatically active homogenates fromP. dichotoma were able to convert both unlabelled and [3H] arachidonic acid into 11-HETE. In vitro biosynthesis of the latter metabolite was also observed with homogenates of the Mediterranean gorgonianParamuricea clavata, another non-prostaglandin-containing soft coral, thus suggesting that 11-R-HETE production is not necessarily accompanied by prostaglandin formation in gorgonian corals.

Porphyrin analysis and coal rank—Porphyrin index of Coalification for bituminous coals

Methods are described for the isolation of gallium, iron and (in a few cases) metal-free porphyrin concentrates from a range of bituminous coals from the United Kingdom and from Poland. The weighted mean molecular mass of the metalloporphyrin homologues in each concentrate is determined, and this, converted to the metal-free value, comprises the Porphyrin Index. This is suggested as an independent scientifically based measure of the degree of coalification of the coal. Different methods of metalloporphyrin analysis suited to this purpose are examined. For gallium porphyrins, reverse phase high-pressure liquid chromatography was the most convenient: for iron porphyrins electron impact mass spectrometry has been used. Where comparisons have been made, there is reasonable agreement between the methods, although differences do exist. Thus hplc was found to be more sensitive to small amounts of more highly degraded systems and tended to give lower values of the Porphyrin Index. The Porphyrin Index in the series studied ranges from about 460 to 410, and decreases as coalification increases. For some Polish bituminous coals, the Porphyrin Index has been tested both laterally and vertically. Thus five different samples from the same seam but at different locations show only a small spread of the index (432–436), whereas samples taken from different depths at a single site (Mikolow 2) show a decreasing index with increasing depth. The lowest index value (413) was found for a highly matured sample from about 1138 m below the surface. As the depth of the sample source increased, the amount of porphyrin concentrate which could be extracted decreased and ultimately became so small that analysis was not feasible. Thus, the highest ranks of bituminous coals, including anthracites, are not amenable to study by way of the Porphyrin Index. The borehole study also revealed a change in co-ordinated metal with depth. At modest depths (174–374 m), iron porphyrins predominated, but below this gallium porphyrins became the more important (but only up to 0.1 ppm). The higher reactivity of iron porphyrins may account for this. Comparisons are made between the Porphyrin Index and mean vitrinite reflectance. This shows a scatter of points when all analytical methods are considered together, but the trend is clear. When the preferred analytical method (hplc of gallium complexes) is used throughout, the plot of mean vitrinite reflectance against Porphyrin Index has a slope of −0.012(5)%; the corresponding slope for electron impact mass spectrometric analysis of iron porphyrins is not significantly different at −0.010(7)%. It is concluded that the Porphyrin Index is a useful and independent indicator of coalification, and its usefulness appears likely to extend into the lignitic range.

Direct analysis of thiophene-containing compounds In Tagetes (Asteraceae) leaf secretory cavities by tandem mass spectrometry

The direct analysis of thiophene-containing compounds present in the leaf secretory cavities of Tagetes (Asteraceae) was obtained by tandem mass spectrometry (MS—MS). In contrast to the usual extraction and chromatographic procedures, leaf glands were pricked with a column injection syringe and the sample was collected directly in a glass capillary. Direct electron impact mass spectrometric analysis of such secretions led to the identification of sulphur containing ionic species, as determined by both isotopic cluster analysis and accurate mass measurements. The molecular ions were easily identifies by parent ion scans and their further structural characterization was achieved by MS—MS.

Identification of mononitropyrenes and mononitrofluoranthenes in air particulate matter via fused silica gas, chromatography combined with negative ion atmospheric pressure ionization mass spectrometry

AbstractThis paper describes the use of high resolution capillary gas chromatography combined with negative ion atmospheric pressure ionization mass spectrometry (NIAPIMS) for the analysis of an air particulate extract for mononitropyrenes and mononitrofluoranthenes, some of which are powerful bacterial mutagens. The results are compared to those obtained by the electron impact mass spectrometric analysis of the same sample In addition, the NIAPIMS method confirmed the identification of 4‐nitropyrene in the ambient air sample.

Quantitation of myo-inositol as its hexakis(trifluoroacetyl) derivative with negative ion chemical ionization mass spectrometry.

Highly volatile hexakis(trifluoroacetyl) derivatives of myo-inositol and hexadeutero-myo-inositol have been prepared and analysed by capillary column gas chromatography/mass spectrometry. The electron impact and negative ion (methane) chemical ionization mass spectra of these compounds have been determined. Negative ion chemical ionization mass spectrometric analysis of hexakis(trifluoroacetyl)-myo-inositol achieves a sensitivity one order of magnitude greater than electron impact mass spectrometric analysis of hexakis(trimethylsilyl)-myo-inositol at appropriate selected ions. Stable isotope dilution measurement of myo-inositol versus hexadeutero-myo-inositol employing gas chromatography/negative ion chemical ionization mass spectrometry of the hexakis(trifluoroacetyl) derivatives is demonstrated, and this method is applied to the detection of inositol derived from hydrolysis of water-soluble inositol phosphates obtained from isolated pancreatic islets.

Electron impact mass spectrometric analysis of mercapturic acid methyl esters. Fragmentation of mercapturic acid methyl esters according to ‘retro-Michael’ reactions

The electron impact mass spectral behaviour of 14 synthetically prepared mercapturic acid methyl esters was examined. The most important and characteristic fragmentation reactions are discussed and special emphasis is made on the occurrence and the mechanism of two fragmentation pathways, which were recognized as ‘retro-Michael’ reactions. In principle, each reaction may result in the formation of two typical ions. In addition, three characteristic ‘key-ions’ originating from the N-acetyl(-l-)cysteine methyl ester part of the mercapturic acids were recognized in all mercapturic acid methyl esters investigated; these ‘key-ions’ can most probably be used as a tool for the qualitative as well as the quantitative analysis of mercapturic acids by gas chromatogra–phy mass spectrometry in biological fluids.

Dealkylation during electron impact mass spectrometric analysis ofN- monoalkylated porphyrin methyl esters

The N-monoethylated, N-monoethylated and N-mono-1-propylated homologues of mesoporphyrin IX dimethyl ester and the corresponding methylated and 1-propylated homologues of coproporphyrin III tetramethyl ester have been prepared. Substituted porphyrins in a series could be distinguished from each other and from the parent porphyrin by their dication absorption spectra. All compounds gave molecular ions of varying intensities during electron impact mass spectrometry but thermal N-dealkylation to mesoporphyrin IX or coproporphyrin III methyl esters occurred readily and it was difficult to obtain spectra not showing fragmentation ions derived from this process. The compounds serve as models for the ‘green pigments’ produced in vivo by the action of some drugs and illustrate the problem of dealkylation during their analysis by electron impact mass spectrometry.