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The Chemistry and Technology of Petroleum
up to 300°C (570°F) and (2) the difficulty of separating isomers for absolute identification. The
sample is usually destroyed, but this is seldom a disadvantage.
Nevertheless, in spite of these limitations, mass spectrometry does furnish useful information
about the composition of feedstocks and products even if this information is not as exhaustive as
might be required. There are structural similarities that might hinder identification of individual
components. Consequently, identification by type or by homologue will be more meaningful since
similar structural types may be presumed to behave similarly in processing situations. Knowledge
of the individual isomeric distribution may add only a little to an understanding of the relationships
between composition and processing parameters.
Mass spectrometry should be used discriminately where a maximum amount of information can
be expected. The heavier nonvolatile feedstocks are for practical purposes, beyond the useful range
of routine mass spectrometry. At the elevated temperatures necessary to encourage volatility, thermal decomposition will occur in the inlet and any subsequent analysis would be biased to the low
molecular weight end and to the lower molecular products produced by the thermal decomposition.
On the other hands, the occurrence of high molecular weight hydrocarbons in ozocerite and
a waxy yellow crude oil from the Uinta Basin (Utah) have been studied successfully by field
ionization-mass spectrometry (FIMS) (Del Río and Philp, 1999). The spectra consisted predominantly of molecular ions ranging up to near mass 2000, and correspond to several series of hydrocarbons ranging up to C 110 . The use of method permitted the range of hydrocarbons identified
in geological materials to be extended far beyond that identified by the usual chromatographic
techniques. Moreover, from the spectra it was possible to extract the molecular ions corresponding to a series of hydrocarbons with different degree of unsaturation or ring closures. The ozocerite solid bitumen consisted mainly of series of branched alkanes (C n H 2n+2 ) and cyclic alkanes
(C n H 2n and C n H 2n–2 ) up to C 110 with a predominance of monocyclic alkanes in the high molecular
weight region (above C 40 ). The waxy yellow crude oil, on the other hand, contained only acyclic
compounds, mainly n-alkanes, ranging up to C 100 .
10.8 CHROMATOGRAPHIC METHODS
Chromatography is the collective term for a set of laboratory techniques for the separation of
mixtures. Typically, the mixture is dissolved in a fluid (mobile phase) which carries it through
a structure holding another material (stationary phase). The various constituents of the mixture
travel at different speeds, causing them to separate. The separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in the partition coefficient
of different compounds result in differential retention on the stationary phase and thus changing
the separation.
A chromatographic technique may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for more advanced use (and is thus a form
of purification). Analytical chromatography generally requires smaller amounts of material and
is used for measuring the relative proportions of analytes in a mixture. The two are not mutually
exclusive.
10.8.1 gAs CHromAtogrAPHy
Gas–liquid chromatography (GLC) is a method for separating the volatile components of various
mixtures. It is, in fact, a highly efficient fractionating technique, and it is ideally suited to the quantitative analysis of mixtures when the possible components are known and the interest lies only in
determining the amounts of each present. In this type of application, gas chromatography has taken
over much of the work previously done by the other techniques; it is now the preferred technique for
the analysis of hydrocarbon gases, and gas chromatographic in-line monitors are having increasing
application in refinery plant control.
The Chemistry and Technology of Petroleum
up to 300°C (570°F) and (2) the difficulty of separating isomers for absolute identification. The
sample is usually destroyed, but this is seldom a disadvantage.
Nevertheless, in spite of these limitations, mass spectrometry does furnish useful information
about the composition of feedstocks and products even if this information is not as exhaustive as
might be required. There are structural similarities that might hinder identification of individual
components. Consequently, identification by type or by homologue will be more meaningful since
similar structural types may be presumed to behave similarly in processing situations. Knowledge
of the individual isomeric distribution may add only a little to an understanding of the relationships
between composition and processing parameters.
Mass spectrometry should be used discriminately where a maximum amount of information can
be expected. The heavier nonvolatile feedstocks are for practical purposes, beyond the useful range
of routine mass spectrometry. At the elevated temperatures necessary to encourage volatility, thermal decomposition will occur in the inlet and any subsequent analysis would be biased to the low
molecular weight end and to the lower molecular products produced by the thermal decomposition.
On the other hands, the occurrence of high molecular weight hydrocarbons in ozocerite and
a waxy yellow crude oil from the Uinta Basin (Utah) have been studied successfully by field
ionization-mass spectrometry (FIMS) (Del Río and Philp, 1999). The spectra consisted predominantly of molecular ions ranging up to near mass 2000, and correspond to several series of hydrocarbons ranging up to C 110 . The use of method permitted the range of hydrocarbons identified
in geological materials to be extended far beyond that identified by the usual chromatographic
techniques. Moreover, from the spectra it was possible to extract the molecular ions corresponding to a series of hydrocarbons with different degree of unsaturation or ring closures. The ozocerite solid bitumen consisted mainly of series of branched alkanes (C n H 2n+2 ) and cyclic alkanes
(C n H 2n and C n H 2n–2 ) up to C 110 with a predominance of monocyclic alkanes in the high molecular
weight region (above C 40 ). The waxy yellow crude oil, on the other hand, contained only acyclic
compounds, mainly n-alkanes, ranging up to C 100 .
10.8 CHROMATOGRAPHIC METHODS
Chromatography is the collective term for a set of laboratory techniques for the separation of
mixtures. Typically, the mixture is dissolved in a fluid (mobile phase) which carries it through
a structure holding another material (stationary phase). The various constituents of the mixture
travel at different speeds, causing them to separate. The separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in the partition coefficient
of different compounds result in differential retention on the stationary phase and thus changing
the separation.
A chromatographic technique may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for more advanced use (and is thus a form
of purification). Analytical chromatography generally requires smaller amounts of material and
is used for measuring the relative proportions of analytes in a mixture. The two are not mutually
exclusive.
10.8.1 gAs CHromAtogrAPHy
Gas–liquid chromatography (GLC) is a method for separating the volatile components of various
mixtures. It is, in fact, a highly efficient fractionating technique, and it is ideally suited to the quantitative analysis of mixtures when the possible components are known and the interest lies only in
determining the amounts of each present. In this type of application, gas chromatography has taken
over much of the work previously done by the other techniques; it is now the preferred technique for
the analysis of hydrocarbon gases, and gas chromatographic in-line monitors are having increasing
application in refinery plant control.