Jan Blomberg

Quantitative Aspects of Comprehensive Two‐Dimensional Gas Chromatography (GC×GC)

A software program was developed to enable the quantification of the complex 3D-data sets as produced by GC×GC. Using this software, it was demonstrated that the detectability limit of GC×GC in our study is 18 times better than that of ‘normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent. Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC) and GC×GC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results of GC×GC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second dimension chromatograms is always present.

Group-Type Identification of Oil Samples Using Comprehensive Two- Dimensional Gas Chromatography Coupled to a Time-of-Flight Mass Spectrometer (GC×GC-TOF)

In this work a comprehensive two-dimensional system (GC x GC) was coupled to a time-of-flight mass spectrometer (TOF/MS) for the analysis of oil samples. Group-types like the alkanes and saturated cyclic compounds (naphthenes), which are present in oil, are shown separately by selecting their unique masses. On selecting appropriate ion fragments, this method also permits the determination of sulfur-and oxygen-containing species in oil. Former results obtained by FID detection could be confirmed. After proper selection of unique ions in GC x GC-TOF both selectivity and sensitivity increase.

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.

Proper Tuning of Comprehensive Two-Dimensional Gas Chromatography (GC×GC) to Optimize the Separation of Complex Oil Fractions

Comprehensive two-dimensional gas chromatography (GC x GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC x GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a nonaromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC x GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.

Gas chromatographic methods for oil analysis

In the past 50 years. gas chromatography (GC) has played a most important role in the analysis of oil. In this review, the early history is briefly reviewed; next developments in this highly relevant application area since about 1985 are highlighted. The main topic of interest are the introduction and decisive role of capillary GC, the use of selective detection techniques, the versatility of coupled-column techniques and, specifically, the additional power of comprehensive two-dimensional GC.

Prediction of comprehensive two-dimensional gas chromatographic separations: A theoretical and practical exercise

Two-dimensional gas chromatography offers an unsurpassed and ordered separation combined with a very high peak capacity. Especially when applied to the separation and quantitative characterisation of complex mixtures it constitutes a leap forward with respect to state-of-the-art capillary GC. This is realised by the two orthogonal separations to which an entire sample is subjected. However, the selection of the proper combination of stationary phases and the temperature program is rather complicated and time consuming. A model is developed to predict which combination of columns is the most appropriate for a specified separation problem. The model is based on calculating retention times and peak widths of the compounds to be separated, on both columns, thus predicting the eventual chromatogram. It starts from estimating the retention factors (k) of the compounds at their elution temperatures. This is performed with the help of the (calculated) vapour pressures and the enthalpic contribution to the activity coefficient as obtained from the Kovats retention indices. Some examples illustrate the usefulness of the model.

Development of an Analytical Marker for the Prediction of Biological Activity of Bitumen Fumes and Bitumens Using the FIA-DMSO Set-Up. Experimental Set-Up and Correlation with Mutagenicity and Carcinogenicity

Abstract During the hot application of bitumen-containing materials, as, for instance, in road paving and roofing, fumes are emitted which contain trace amounts of polycyclic aromatic compounds (PACs). The PAC levels are very low, and from the available epidemiological studies, there is no evidence that human exposure to bitumen or its fumes results in any cancer risk to the workforce. For comparative purposes we are trying to identify a laboratory “marker” for bitumen fume condensates (BFCs) which will give a correlation with biological activity and hence carcinogenic potential. Previously it was found that the determination of total 3–6-ring PACs by DMSO extraction followed by gas chromatographic analysis, whose use is well established for mineral oils, showed promise as a marker for BFCs as well. Because standard DMSO extractions require about 4 g of sample, whereas generally only one mg or less of bitumen fume can be sampled, we developed a micro extraction technique, using Flow Injection Analysis (FIA). The FIA-DMSO extraction was coupled with normal phase liquid chromatography (NPLC) followed by gas chromatography with flame ionisation detection. Only 9 μl of sample solution in cyclohexane (at least 2% m/v) is injected into a cyclohexane stream and extracted with DMSO in the FIA coil. A 50 μl cut from the DMSO stream is introduced into a tetrahydrofurane (THF)/n-octane (50/50) stream to the NPLC-column. A 608 μl fraction of the THF/octane stream after the NPLC column, comprising the time window in which the standard EPA 2–6 ring PAC mixture elutes, is directly introduced into the retention gap. After evaporation of most of the solvent in the retention gap, the concentrated analyte is swept into the GC for the quantitative analysis using the FID. The system is selective towards the biologically most active fraction, the unsubstituted and lightly substituted PACs. The 3–6-ring PAC content by FIA-DMSO correlates well with the Mutagenicity Index (MI) of the Mobil modified Ames test (R2= 0.927), these data have been measured on a wide range of materials ranging from bitumen fume condensates, distillate luboils to heavy residual materials such as bitumens. The residual products have to be freed from the heaviest molecules by pentane precipitation. The 3–6-ring PAC content also correlates with carcinogenicity in mouse skin-painting bioassays. This technique enables us to assess the carcinogenic hazard of potential new feedstocks, processing routes and products in an early stage of development.

Chapter 7 Petrochemistry

Publisher Summary This chapter discusses the application of 2D gas chromatography (GCxGC) in a petrochemical sample analysis. The majority of petrochemical analyses involve a group-type separation rather than a target analysis. Most of the target analyses performed in petrochemistry are analyses of heterocompounds—that is, analyses of oxygenates or sulfur- or nitrogen-containing compounds. The GCxGC–flame ionization detector (FID) is used for quantification. The collected data from detectors in GCxGC are reorganized to produce meaningful results, and several manufacturers produce software dedicated to this technique. The chapter presents the use of chemometric techniques, such as multivariate analyses (MVA), the generalized rank annihilation method (GRAM), PARAFAC, and trilinear partial least squares (tri-PLS) to improve or extend the results.