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This simulator was developed to help students
beginning the study of gas chromatographic instruments to
understand their operation. It is not meant to teach
chromatographic theory. The instrument simulator is divided into
5 sections. One is for sample preparation. Another is used
to manage carrier gases and choose a detector and column.
The third sets the conditions for either isothermal or
programmed temperature operation. A fourth section models manual
injections, and the fifth is the autosampler.
The operator has a choice among 6 columns of
differing diameters and packing polarities and a choice of
either isothermal or simple one-stage temperature
programming. The simulator can be operated in either single-sample
mode or as a 10-sample autosampler. The integrator has two
modes of operation, a "dumb" mode in which only the
retention time, area of the peak, and percentage area are listed and
a "smart" mode that also lists the components' identities.
The identities are obtained from a list of names and
retention times created by the operator. Without this list only the
percentages and areas are listed. The percentages are based
on the areas obtained from the chromatogram and not on
the actual percentages assigned during sample preparation.
The data files for the compounds used in the
simulator are ASCII files and can be edited easily to add more
compounds than the 11 included with the simulator. A
maximum of 10 components can be used in any one
sample. Sample mixtures can be made on a percent-by-volume
basis, but not by mass of sample per volume of solvent. A
maximum of 30 compounds can be present in any one file,
but the number of files is limited only by the operating
system. (I suggest that not more than 20 compounds be used in
any one file, as scrolling through large numbers of compounds
is annoying to say the least.) File construction and layout
are discussed in detail in the User's Manual.
Chromatograms are generated by calculating a
retention time based on the difference between the boiling point
of the component and the temperature of the column. The
polarity difference between the column packing and the
component is also used to modify the retention time. The
retention time decreases as the difference between the boiling
point of the component and the temperature of the column
increases, and retention time increases as the polarity of
the component approaches the polarity of the column. If the temperature of the column is too low, a warning message is
given and the chromatogram does not show that component.
There is no "carry-over" to the next chromatogram, as might be
the case for an actual instrument. Carrier-gas flow rate is
fixed and is not part of the retention-time calculation. Because
of this latter condition and the method used to determine
retention time, this simulator is not useful for gas
chromatography method development and is not intended for such use.
The purpose of the simulator is to give a beginning
student experience in what happens as column temperature
is varied, why one might need temperature programming,
why an autosampler might be useful, and the pitfalls of
"smart" integrators. When students make mistakes in
instrument setup with the simulator the consequences are not
damaging to the simulator but might cause serious problems with a
real instrument.
Hardware and Software Requirements
Hardware and software requirements for
A GC Instrument Simulator are shown in Table 1.
Shown (right to left) are the main instrument
control window and the manual injection window from
A GC Instrument Simulator.
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