P.J. Arpino

Optimization of the instrumental parameters of a combined liquid chromatograph-mass spectrometer, coupled by an interface for direct liquid introduction : II. Nebulization of Liquids by Diaphragms

Abstract Direct liquid introduction interfaces for combined liquid chromatography-mass spectrometry (LC-MS) require a flow restriction to limit input liquid flow-rates to the small values tolerated by the mass spectrometer. In general, viscous type restrictions should be avoided. A non-viscous type restriction such as a 1-3-μm pinhole in a thin wall is acceptable for LC-MS as it produces a jet of small droplets of solution. However, jet instabilities affecting the mass spectral fragmentation pattern directly cannot be avoided in this simple nebulizer. Adding a hot gas to the ion source gives control of chemical ionization reactions and provides thermal energy for droplet vaporization, thus improving overall LC-MS performances. Application to analyses of monosaccharides and disaccharides illustrates the present state of the art of the technique.

Investigation of high-molecular-weight carboxylic acids in petroleum by different combinations of chromatography (gas and liquid) and mass spectrometry (electron impact and chemical ionization)

Abstract High-molecular-weight carboxylic acids from various crude oils were analysed using a combination of chromatographic techniques: liquid chromatography on a modifed absorbent, thin-layer chromatography, glass capillary gas chromatography and combined gas chromatography—mass spectrometry. The polycyclic acids of the hopane series were investigated becase of their importance as biological markers in correlation problems.

Identification of carbazoles and benzocarbazoles in a coker gas oil and influence of catalytic hydrotreatment on their distribution

Abstract Fractions highly enriched in pyrrole benzologues have been extracted from a coker gas oil before and after hydrotreatment under selected operating conditions. Carbazole, methyl- and dimethylcarbazoles and benzocarbazoles have been identified by means of g.c. coelutions with standards. The study of these compounds after catalytic hydrotreatment has shown that benzocarbazoles are more effectively removed than carbazoles in highly hydrogenating conditions (partial pressure of hydrogen, 10 MPa; temperature, 360 °C) whereas alkyl carbazoles and more particularly 1-methyl derivatives are more altered at a high temperature (380 °C, partial pressure of hydrogen, 5 MPa).

Distribution of carbazole derivatives in petroleum

Abstract Carbazole, its alkyl derivatives and higher benzologs have been selectively isolated from six different crude oils. In all samples, benzocarbazoles are major constituents of a series which may extend up to dibenzocarbazole derivatives. The distribution includes unsubstituted parent compounds and shows a maximum content of methyl and dimethyl substituted species. Sixteen individual constituents have been identified by means of comparison with reference compounds using gas chromatography, mass spectrometry and high resolution spectrofluorimetry. So far, no generally acceptable explanation has been given for the origin of these compounds, which presumably are the most stable ones in their respective series of aromaticity. Thus, carbazole derivatives may result from a complex sequence of reactions during kerogen formation, not allowing the recognition of precursing molecules. The geochemical significance of this series of nitrogen compounds needs to be clarified, requiring further studies.

Isolation of degraded pentacyclic triterpenoid acids in a Nigerian crude oil and their identification as tetracyclic carboxylic acids resulting from ring A cleavage

Abstract Three tetracyclic acids were identified in a Nigerian crude oil, after reduction and deuterium labelling followed by GC/MS investigation. Two of them are identical to 3:4 seco acids previously identified in sediments. The third one is a novel C 24 acid that has not been reported up to now. These geochemical markers are assumed to belong to the class of photochemical tetracyclic triterpenes formed by decay of pentacyclic 3-ketoterpenoids.

Identification of nitrogen bases in a coker gas oil and influence of catalytic hydrotreat ment on their composition

Abstract The investigation of nitrogen bases occurring in a coker gas oil before and after catalytic hydrotreatment has shown important differences in reactivity of azaarenes. Compounds with a low degree of aromaticity are relatively resistant compared with higher benzologues. Particularly stable are α-methylated azaarenes, which are also major nitrogen bases found in crude oils. Alkyl anilines, the last intermediates before denitrogenation, are the most abundant bases in hydrotreated samples.

Construction of a supercritical fluid chromatograph-mass spectrometer instrument system using capillary columns, and a chemical ionization source accepting high flow-rates of mobile phase

Abstract An instrument combining capillary supercritical fluid chromatography (SFC) and mass spectrometry (MS) with chemical ionization is described. Stable experimental SFC-MS conditions were obtained when utilizing a short restrictor at the end of a SFC capillary column, typically a 3 mm × 5 μm I.D. fused-silica capillary tube. The vacuum pumping capacity of the mass spectrometer and the special design of the ion source permitted supercritical fluid flow-rates up to 50 μl/min to be used. Preliminary results obtained with polynuclear aromatic hydrocarbons and various lipids are reported.

Optimization of the instrumental parameters of a combined liquid chromatograph-mass spectrometer, coupled by an interface for direct liquid introduction : III. Why the solvent should not be removed in liquid chromatographic-mass spectrometric interfacing methods

Abstract Recent advances in the application of mass spectrometry to the analysis of involatile samples in solution in organic solvents are reviewed. It appears that ions pre-formed in solution by protonation or cationization of the sample molecule can be released in the gas phase by supplying energy to the solution. The results could

Occurrence of novel tetracyclic geochemical markers: 8,14-seco-hopanes in a Nigerian crude oil

Abstract The occurrence of a novel class of tetracyclic triterpanes in petroleum is reported. These compounds presumably derive from pentacyclic hopanes by ring C opening. The identification of one C30H54 8,14-seco-hopane has been effected by means of comparison with a mixture of synthetic isomeric compounds. Homologous seco-hopanes parallel the distribution of hopanes between C27 and C30.

Packed-column supercritical fluid chromatography coupled with electrospray ionization mass spectrometry

Abstract A new approach to combined supercritical fluid chromatography—mass spectrometry (SFC-MS) was explored using a two-pump supercritical fluid chromatograph, and a packed column with the outlet directly interfaced to an electrospray (ES) ion source attached to a single quadrupole mass spectrometer. The experimental set-up is described and preliminary results are reported for mobile phase flow-rates in the range 0.15–1 ml/min, using CO2 modified by the addition of 1–30% (v/v) of a polar organic solvent. The combined system has a greater potential for the analysis of polar molecules by MS than earlier SFC-MS instruments that utilized capillary column SFC directly coupled to the ion source of a chemical ionization mass spectrometer. A liquid-phase ionization process was utilized for solute ion formation, and it could be applied to the determination of high-mass and polar molecules separated by packed column SFC; however, the MS response is dependent on the mobile phase composition and the SFC-ES-MS instrument is still limited to the determination of low-mass samples owing to cold trapping on some critical surfaces.