6 Gas Chromatography Columns Using Ionic Liquids …
153
Analysis of alkyl phosphates is of utmost importance due to the problems they pose
in petroleum refining processes [125]. A relationship between molecular structure
and GC retention of alkyl phosphates was established by employing a series of ionic
liquid columns [126]. The dependence of elution order on separation temperature
for a homologous series of alkyl phosphates was observed on the three ionic liquid
columns with highest polarities (i.e., SLB-IL82, SLB-IL100, and SLB-IL111). It was
found that at high temperatures, the elution order was reversed with trioctyl phosphate
eluting before trihexyl phosphate. Moreover, a thermodynamic model was developed
to predict the interactions between alkyl phosphates and IL stationary phases. Subsequently, the SLB-IL100 column was found to have the optimal selectivity for
separation of short-chain alkyl phosphates from petroleum hydrocarbons.
The SLB-IL59 column was utilized for high-temperature GC × GC separation of
high-boiling point species in heavy petroleum fractions [127, 128]. The IL59 column
provided enhanced separation between neutral and basic nitrogen-containing PACs
and provided quantitative distribution of acridines and carbazoles in heavy matrices
[127]. In addition, an unprecedented group-type separation of heavy sulfur species
including naphtheno-aromatic S-compounds family was achieved in vacuum gas oil
(VGO) using a SLB-IL59 column in reversed mode 2D GC [128].
Ionic liquid columns were evaluated for characterization of sulfur and nitrogen
compounds in Brazilian petroleum derivatives with comprehensive 2D GC [129]. The
normal configuration comprised of the DB-5MS/IL59 provided the best orthogonality for separation of organic sulfur compounds (OSCs), while nitrogen compounds
were better fractioned using IL59/DB-5MS reversed mode. The matrix interference
that resulted from coelution of OSCs and PAHs was significantly eliminated by
using ionic liquid columns. Consequently, a higher number of sulfur compounds
was detected in comparison with the utilization of traditional stationary phases.
6.7 Water Analysis
The accurate quantification of water is one of the most ubiquitous yet important
analytical measurements worldwide [130]. Water content is measured at a broad
range of concentrations (from sub-ppm levels to above 99%) in a greater array of
matrices than any other analytes [131]. Measuring water is usually mandated by
regulatory agencies in certain products including foodstuffs, pharmaceuticals, and
other consumer products [132]. Given the fact that water is an omnipresent interfering constituent in hydrophilic samples, further challenges may be met in accurately
quantifying trace amounts of moisture [131]. Several analytical techniques have been
developed depending on the nature of the sample and the amount of moisture present
to effectively determine the water content. Accordingly, a widely used approach for
most sample types is highly desirable. Refractive index (RI) measurement, gravimetric determination of water loss after drying (LOD), and Karl Fischer titration (KFT)
are the most recurrent methods for determination of water [130]. However, there are
153
Analysis of alkyl phosphates is of utmost importance due to the problems they pose
in petroleum refining processes [125]. A relationship between molecular structure
and GC retention of alkyl phosphates was established by employing a series of ionic
liquid columns [126]. The dependence of elution order on separation temperature
for a homologous series of alkyl phosphates was observed on the three ionic liquid
columns with highest polarities (i.e., SLB-IL82, SLB-IL100, and SLB-IL111). It was
found that at high temperatures, the elution order was reversed with trioctyl phosphate
eluting before trihexyl phosphate. Moreover, a thermodynamic model was developed
to predict the interactions between alkyl phosphates and IL stationary phases. Subsequently, the SLB-IL100 column was found to have the optimal selectivity for
separation of short-chain alkyl phosphates from petroleum hydrocarbons.
The SLB-IL59 column was utilized for high-temperature GC × GC separation of
high-boiling point species in heavy petroleum fractions [127, 128]. The IL59 column
provided enhanced separation between neutral and basic nitrogen-containing PACs
and provided quantitative distribution of acridines and carbazoles in heavy matrices
[127]. In addition, an unprecedented group-type separation of heavy sulfur species
including naphtheno-aromatic S-compounds family was achieved in vacuum gas oil
(VGO) using a SLB-IL59 column in reversed mode 2D GC [128].
Ionic liquid columns were evaluated for characterization of sulfur and nitrogen
compounds in Brazilian petroleum derivatives with comprehensive 2D GC [129]. The
normal configuration comprised of the DB-5MS/IL59 provided the best orthogonality for separation of organic sulfur compounds (OSCs), while nitrogen compounds
were better fractioned using IL59/DB-5MS reversed mode. The matrix interference
that resulted from coelution of OSCs and PAHs was significantly eliminated by
using ionic liquid columns. Consequently, a higher number of sulfur compounds
was detected in comparison with the utilization of traditional stationary phases.
6.7 Water Analysis
The accurate quantification of water is one of the most ubiquitous yet important
analytical measurements worldwide [130]. Water content is measured at a broad
range of concentrations (from sub-ppm levels to above 99%) in a greater array of
matrices than any other analytes [131]. Measuring water is usually mandated by
regulatory agencies in certain products including foodstuffs, pharmaceuticals, and
other consumer products [132]. Given the fact that water is an omnipresent interfering constituent in hydrophilic samples, further challenges may be met in accurately
quantifying trace amounts of moisture [131]. Several analytical techniques have been
developed depending on the nature of the sample and the amount of moisture present
to effectively determine the water content. Accordingly, a widely used approach for
most sample types is highly desirable. Refractive index (RI) measurement, gravimetric determination of water loss after drying (LOD), and Karl Fischer titration (KFT)
are the most recurrent methods for determination of water [130]. However, there are