Wim Genuit

Comparison of comprehensive two-dimensional gas chromatography and gas chromatography : mass spectrometry for the characterization of complex hydrocarbon mixtures

In this paper, we compare the current separation power of comprehensive two-dimensional gas chromatography (GCxGC) with the potential separation power of GC-mass spectrometry (GC-MS) systems. Using simulated data, we may envisage a GC-MS contour plot, that can be compared with a GCxGC chromatogram. Real examples are used to demonstrate the current potential of the two techniques in the field of hydrocarbon analysis. As a separation technique for complex hydrocarbon mixtures, GCxGC is currently about as powerful as GC-MS is potentially powerful. GC-MS has not reached its potential separation power in this area, because a universal, soft ionization method does not exist. The greatest advantage of GCxGC is, however, its potential for quantitative analysis. Because flame-ionisation detection can be used, quantitative analysis by GCxGC is much more robust, reliable and reproducible.

Analysis of fresh triterpenoid resins and aged triterpenoid varnishes by high-performance liquid chromatography–atmospheric pressure chemical ionisation (tandem) mass spectrometry

Fresh triterpenoid (dammar and mastic) resins and aged triterpenoid varnishes were analysed by on-line HPLC–MS using atmospheric pressure chemical ionisation (APCI). Twenty components were identified in the fresh resins [dammarenolic acid, ursonic acid, oleanonic acid, hydroxydammarenone (I and II), dammaradienol, oleanonic aldehyde, dammarenediol, ursonic aldehyde, oleanolic aldehyde, ursolic aldehyde, hydroxyhopanone, dammaradienone, moronic acid, (3l,8R)-3,8-dihydroxypolypoda-13E,17E,21-triene, (8R)-3-oxo-8-hydroxypolypoda-13E,17E,21-triene, masticadienonic acid, isomasticadienonic acid, 3-O-acetyl-3-epimasticadienolic acid and 3-O-acetyl-3-epiisomasticadienolic acid]. Analysis of the aged varnishes revealed the presence of some oxidised triterpenoid components [11-oxo-oleanonic acid, 11-oxo-oleanonic acid, 3-oxo-25,26,27-trinordammarano-24,20-lactone, 20,24-epoxy-25-hydroxy-3,4-seco-4(28)dammaren-3-oic acid and some ocotillone type molecules]. Most constituents of these complex samples were well resolved by reversed-phase HPLC. APCI-MS provides useful information about the molecular mass and the presence of certain functional groups. Specific marker compounds were found, which enable the discrimination between aged dammar and mastic varnishes by HPLC–APCI-MS. The fragmentation behaviour of triterpenoids under APCI conditions was compared to that under electron impact conditions. Mass spectrometric fragmentation of triterpenoids with a saturated ring system is straightforward. Triterpenoids with an unsaturation in the ring system probably give rise to double bond migration. Subsequent low energy MS–MS analysis does not provide more structural information, since mainly non-specific ring fragment ions are formed.

Pyrolysis-gas chromatography-photoionization-mass spectrometry, a new approach in the analysis of macromolecular materials

Abstract A Curie-point evaporation/pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) instrument is described in which a fused-silica capillary column is coupled directly both to the pyrolysis unit and to the ion source of a photoionization mass spectrometer. Photoionization by means of a rare gas resonance lamp was used as the low-energy ionization technique. The performance of the instrument was tested with a Grob test mixture at photoionization energies of 11.8 eV (Ar I) and 10.6 eV (Kr I). Photoionization mass spectra of 1-octanol, methyl octanoate, dimethylaniline and n-dodecane obtained at these energies are discussed. Py-GC-photoionization-mass spectrometry (PIMS) and PIMS data for the (1 → 4)-α-glucan amylose are presented and compared with electron impact (EI) Py-GC-MS and Py-MS results. The cumulative Ar I photoionization mass spectrum of the GC-MS data on amylose closely resembles the 14-eV EI spectrum of amylose. The method is a promising alternative to the existing low-voltage EI ionization mass spectrometry for the pyrolysis analysis of macromolecular materials.

Improving the ion current stability of a thermospray source by improving the control of the vaporizer temperature and solvent flow-rate

Abstract The Original time-proportional vaporizer temperature control system of the thermospray source has been changed into a system based on phase-angele control, which enahces the vaporizer temperature stability, and hence the ion current stability of the source. When combined with a solvent pressure stabilization system, this new temperature control system stabilizes the vaporizer temperature to within 0.1°C of the set value.

Applications of dual-beam thermospray liquid chromatography—mass spectrometry

A dual-beam thermospray system has been constructed, by which the requirements of the electrolyte ion evaporation process have been decoupled from those of the separation and volatilization of the analytes. The dual-beam system has a high flexibility with regard to mobile phase polarity, flow-rate and eluent vaporizer temperature. Results are presented from applications of dual-beam thermospray in the coupling of organic gel permeation chromatography with mass spectrometry, and in gradient elution liquid chromatography. In a comparison of the dual-beam with the single-beam thermospray technique for two thermolabile compounds, the mass spectra obtained with the dual-beam system show much less degradation.

Comprehensive two-dimensional liquid chromatography of heavy oil

Heavy oil refers to the part of crude oil that is not amenable to further distillation. Processing of these materials to useful products provides added value, but requires advanced technology as well as extensive characterization in order to optimize the yield of the most profitable products. The use of comprehensive two-dimensional liquid chromatography (LC × LC) was investigated for the characterization of de-asphalted short residue, also called maltenes. Initial studies were performed on a polycyclic aromatic hydrocarbon standard, an aromatic extract of hydrowax, and the fractions obtained after solvent fractionation of the maltenes. Cyanopropyl- and octadecyl-silica were used as first-dimension and second-dimension columns, respectively. The analysis of the maltenes and fractions thereof required a change in first-dimension stationary phase to biphenyl as well as an increase in modifier strength to improve recovery. The extensive characterization of maltenes with LC × LC within four hours was demonstrated. The Program for the Interpretive Optimization of Two-dimensional Resolution (PIOTR) has been applied to aid the method development, but due to the absence of specific peaks in the chromatograms it was challenging to apply to the maltenes or its fractions. Nonetheless, an approach is suggested for resolution optimization in cases such as the present one, in which regions of co-elution are observed, rather than clearly separated peaks.

Historical mystery solved: a multi-analytical approach to the identification of a key marker for the historical use of brazilwood (Caesalpinia spp.) in paintings and textiles

Dyes derived from brazilwood (Caesalpinia spp.) are known to have been used in a diverse range of objects, from Medieval European textiles to North American First Nations objects, while pigments made from brazilwood feature in the palette of a number of painters, including Rembrandt and Van Gogh. For almost two decades, an unknown marker has been used to detect brazilwood colourants in historical objects. Limited sampling opportunities mean that the identification of the chemical structure of this marker has eluded scientists to date. Using a combination of synthesis, UPLC-ESI-MS/MS, HPLC, NMR and GC-MS, the identity of this unknown marker was confirmed as the benzochromenone, urolithin C. Structural identification provides a reliable reference compound for use across a range of analytical techniques employed in the cultural heritage sector and will enable the future development of non-destructive techniques for its identification on high-status objects.

Applications of Mass Spectrometry in an Industrial Research Laboratory

Mass spectrometry has many applications in the research laboratory of Shell in Amsterdam, including: high resolution studies of oil feedstocks and products, identification of components in complex mixtures, and accurate mass measurements of a number of compounds. Of all of these applications examples are given.