AdvancedGasChromatography–Progress inAgricultural, Biomedical and Industrial Applications
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In gas chromatograph the chromatography column is placed in the oven, after the injector
and before the detector. Between the injector and the column a
retention gap
or
guard column
is often installed
.
Its length is 0.5-5.0m and it is actually a deactivated fused-silica tube. In
this retention gap
the condensed solvent resides after injection, but it is removed by
vaporization. The role of a guard column is to collect the non-volatile compounds and
particulatematter from samples in order to avoid their penetration in the chromatography
column andmaintain the lifetimeof the column.
Conditioning of chromatography columns is recommended for residual volatiles’ removal.
For capillary column conditioning there are three steps to follow:
1.
Carrier gas flow has to be constant when column temperature is higher than room
temperature.
2.
The maximum temperature of the stationary phase or of the column must not be
transcendedbecause the chromatography column couldbedamaged.
3.
For capillary column, in order to obtain a steady baseline, it is indicated only to purge
carrier gas flow for 30 min at ambient temperature and then, with a rate around
4ºC/min, elevate the temperature slightly over the maximum temperature limit and
maintain for several hours. The first twoprocedures are also applicable for conditioning
of apacked column.
Whennon-volatiles andparticulatematter are accumulatingon the inlet of the columnor on
the injector liner, the chromatography column is contaminated and it is no longer working
to its full potential. This is reflected mostly in peak tailing and changes in the retention
characteristics of the column. Column reactivation could be realized either by removing the
inlet part of the column (1-2 meters) or by turning the column around and then applying
step 3 for a longer time. The extreme solution is to remove the solvent.
13. Practical applicationofGCanalysis formixturesof hydrocarbons
One of the fieldswhereGC is increasingly used is in the oil and gas industry, and specially
the refinery sector. In refineries theGC is usednot only for identifying the components from
amixture, and then concentration, but alsoas an integrate tool for loop control.
The gas mixture that youmay find on a refinery is usually called “refinery gas”, and is a
mixture of various gas streams produced in refineryprocesses. It canbeused as a fuel gas, a
final product, or a feedstock for further processing. An exact and fast analysis of the
components is essential for optimizing refinery processes and controlling product quality.
Refinery gas stream composition is very complex, typically containing hydrocarbons,
permanent gases and sulphur.
In this practical example ofGCuse in a refinery, the hydrocarbonmixturewas an industrial
C5 cut separated from a Fluidized Catalytic Cracking (FCC) plant. Table 9 (Comanescu &
Filotti, 2010).
The gas chromatograph was a HP 5890 Series II apparatus, with a configuration and
operating parameters similar to those for PONA analysis (ASTMD 6293-98). Commercially
available standard (Agilent) for refinery gas analysis was employed for calibration of both
hydrocarbons retention times and concentrations.
