Pa Piet Leclercq

Evaluation of time-of-flight mass spectrometric detection for fast gas chromatography.

Separations below 1 s of a mixture of organic compounds ranging from C5 to C8 have been performed to investigate the performance of a time-of-flight mass spectrometer in fast gas chromatography. The gaseous samples were focussed on a cold trap, and then injected after thermal desorption to obtain the required narrow input band-widths. Also, to obtain a very fast separation, a short narrow bore column was used, operated at above-optimum inlet pressures. With this system, it was possible to identify ten compounds within 500 ms, showing peak-widths (2.354sigma) as narrow as 12 ms. The spectral acquisition rate used for these analyses was 500 Hz. The quality of the recorded spectra and the comparison with library spectra was very high. Deconvolution algorithms offer the possibility of identifying overlapping peaks. It is shown that the spectral scan speed of the time-of-flight mass spectrometer is high enough for very fast separations.

Chemical Composition of the Oil of Ageratum conyzoides L. from Vietnam

ABSTRACT The essential oil of Ageratum conyzoides L. was analyzed by capillary gas chromatography and mass spectrometry. The main constituents were ageratochromene (precocene II), 6-demethoxyageratochromene (precocene I) and β-caryophyllene, accounting for 77% of the oil.

Essential Oil of Eaglewood Tree: a Product of Pathogenesis

Abstract The essential oil of eaglewood tree (Aquilaria agallocha Roxb.) has been considered to be a pathological product. An investigation was carried out to study the difference in composition of oils obtained from healthy, naturally infected and artificially inoculated eaglewood using GC and GC/MS analyses. This investigation showed a marked difference in the oil compositions among the treatments with regards to their quality. Valerianol (3.0%) and tetradec-anioc acid (7.1%) contents were recorded higher in the oils of naturally infected plants than in that of healthy ones (0.1% and 6.9%, respectively). Pentadecenoic acid was totally absent in the oils of healthy, whereas it was found in a greater amount (6.8%) in the oil of naturally infected plants. In contrast, dodecanoic acid (3.1%), pentadecanoic acid (6.2%), hexadecanoic acid (31.5%) and octadecanoic acid (4.1%) were found in a higher amount in the oils of healthy plants, while the oils obtained from naturally infected plants contained lower amounts of these components (2.5%, 4.8%, 20.0% and 1.0%, respectively). The oils obtained from the inoculated plants showed almost similar distribution of the components with healthy plants.

Syn-anti isomerisation of 2,4-dinitrophenylhydrazones of volatile carbonyl compounds in capillary gas chromatographic-mass spectrometric analyses

Dinitrophenylhydrazone derivatives of volatile aldehydes and ketones were investigated by high-performance liquid chromatography (HPLC) and by gas chromatography-mass spectrometry (GC-MS). HPLC separations were slightly better than those obtained by existing procedures, but high-resolution GC is the method of choice. The equilibrium of the syn-anti isomerization of the compounds is influenced by the nature of the solvent, the deactivation of the column and the injection and column temperatures. The GC profile can therefore be controlled by careful selection of the experimental conditions. It is shown that this phenomenon, in addition to the occurrence of characteristic values of the difference in the retention indices of syn and anti isomers for a given compound, can facilitate the identification. Chemical ionization (methane) mass spectra of the compounds were found to contain more information than conventional electron impact spectra. Characteristic fragment ions are tabulated.

Gas chromatography and mass spectrometry of bis(alkylamino)-s-Triazines

The retention behaviour of 22 2-chloro, 2-methoxy- and 2-methylthio-4,6-bis(alkylamino)triazines was studied on four gas chromatographic columns with different polarities. The most polar stationary phase Carbowax 20M, was found to be the best suited for the separation of these compounds. The differences in the retention indices of the same triazines on columns with different polarities were found to be proportional to the pKa values and the dipole moments of these compounds. Electron-impact mass spectra and deduced fragmentation schemes are given. The stability of the compounds under electron impact increases in the order chloro < methoxy < methylthio derivatives. Chemical-ionization mass spectra, using methane as reagent gas, are tabulated. It has been found that the ease of fragmentation of the protonated molecular ions of chlorotriazines is related to the low proton affinity of the leaving neutral HCl group. In the isobutane chemical-ionization mass spectra all triazines exhibited the protonated molecular ion as the base peak with only relatively minor fragmentations.

Essential oils of Curcuma longa L. from Bhutan

Abstract The essential oils of Curcuma longa L. (Zingiberaceae) were isolated from its rhizomes and leaves by hydrodistillation. The oils were analyzed by high resolution GC and GC/MS. The rhizome oils contained more than 40 constituents, of which the major ones were α-turmerone (30–32%), ar-turmerone (17–26%) and β-turmerone (15–18%). The leaf oil contained about 60 compounds and the main constituents were α-phellandrene (18.2%), 1,8-cineole (14.6%) and p-cymene (13.3%).

Composition of the essential oil of Eryngium foetidum L. from Vietnam

ABSTRACT The essential oil of the aerial parts of Eryngium foetidum L. of Vietnamese origin has been analyzed by a combination of GC and GC/M S. Nineteen components have been identified, of which the major ones were found to be (E)-2-dodecenal (45.5%) and 2-dodecenoic acid (15.5%). The other constituents of this oil are also mainly aldehydes and acids.

Determination of the underivatized antineoplastic drugs cyclophosphamide and 5-fluorouracil and some of their metabolites by capillary gas chromatography combined with electron-capture and nitrogen-phosphorus selective detection.

A rapid and sensitive method for the determination of cyclophosphamide (CP) and 5-fluorouracil (5-FU) and some of their metabolites in one analysis has been developed. Surface-coated open-tubular OV-275 columns were combined with electron-capture detection and nitrogen-phosphorus selective detection. The influence of the column diameter on the separation is shown. Extraction with 2-propanol-diethyl ether (22:77) allows the isolation of CP, 5-FU and their analogues in one extraction step. The assay was applied to some pharmacokinetic experiments with chemotherapeutically treated patients and with a WAG/Rij rat.

Increased speed of analysis in directly coupled gas chromatography-mass spectrometry systems. II.Advantages of vacuum outlet operation of thick-film capillary columns

Abstract It is shown that direct insertion of the end of a capillary column into the ion source of a mass spectrometer increases the speed of analysis compared with atmospheric outlet conditions. This applies to thin-film columns, as reported previously [C. A. Cramers, G.J. Scherpenzeel and P.A. Leclercq, J. Chromatogr. , 203 (1981) 207], as well as to the thick-film capillaries treated in this paper. For thick-film columns th enegative effect of diffusion in the stationary liquid phase on the speed of analysis, via an increased minimal plate height and a decreased optimal gas velocity, is more than compensated for by the effects of vacuum outlet operation. The gas chromatographic-mass spectrometric (GC-MS) coupling of capillary columns directly inserted into the ion source posesses the favourable properties of full sample transfer, no catalysis or adsorption in an interface and increased speed of analysis. Thick-film columns offer in addition a considerably increased sample capacity. The resolution of low-boiling compounds is enhanced and adsorption on the column wall is masked by the thicker film. Further, thick-film columns are less demanding with respect to instrument specifications such as speed of sampling, time constants and noise levels of detection and registration systems. The conclusion is that the best GC-MS interface appears to be no interface at all but rather direct insertion of the column end into the ion source.

Essential Oil of Curcuma amada Roxb. from Northeastern India

ABSTRACT The essential oil, which was obtained by water distillation of the fresh rhizomes of Curcuma amada Roxb. (Zingiberaceae) growing in the plain districts of Northeastern India, was investigated by GC/MS. Nine components (97.4%) were identified. Myrcene was found as the major (88.6%) component.