BuiltWithNOF

Linear / linear, or linear / logarithmic, or combined application of EXPORT data files
in graphics mode:
what is more helpful to make correct chromatogram evaluation ? Here are examples.
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Figure 1:
a linear line chromatogram from a temperature programmed capillary separation of a diesel oil sample, showing mainly saturated n-alkanes.
This sample should be compared with an older diesel oil sample. The question was: Is an aging visible ?
The line chromatogram technique has several modes to simplify this task. At first one should really compare both chromatograms. This is shown in figure 2. Some digital data are shown “here”.

Figure 2:
File 00000054.EXP (without entered retention index data) is directly compared with file 00000057.EXP (with entered retention index data as result of an in line identification, see later).
It looks like that there are differences in the traces but not at all in the quantitative and qualitative composition of the main compounds, the saturated hydrocarbons. Click onto the blue “here” above in order to see digital data.

Figure 3:
There are really differences in the trace range of compounds, which for sure are NOT n-alkanes, as they elute between  consecutive homologues.
This means, aging of the diesel sample 00000054.EXP versus 00000057.EXP exists. The next question should be:
How much ? In which C-range ? Or any other question but supported by line chromatograms. The “line chromatogram software” allows a lot of modes. See figure 4.

Figure 4:
In order to see the changes qualitatively and quantitatively accurate, the linear / linear comparison of both line chromatograms can be made as sharp as the separation efficiency of the capillary chromatograms allows. Thus a look into the retention time range from tms 300 seconds up to tms 500 seconds and in the concentration range of 1 % for a full scale representation one sees clearly:
The aging takes and makes substances. see under fig.1.
 

Figure 5:
The line chromatogram figure 5 shows the retention index range in which the diesel oil analysis is done: starting with C8, ending at C32. The sharp chromatogram end is possible by a backflush technique. All details to those important instrument modifications are described in IfC TEACHWARE. The non- n-alkan traces are well visible using a LOG / INDEX line chromatogram mode. Substance concentrations between 0.01 and 0.1 area %.
 

The aging of a product produces substances also in much lower concentrations than shown here. To make this visible depends on the conditions for the integration software, the detector sensitivity and the trace analysis conditions selected. The here reported analyses were done above the low trace level, as the question was not a full range research but more simple: is there an aging truly visible and for sure also a fact for a critical customer ? Analysis often must be done a way that also OTHERS can accept the results.
Trace effects are especially well visible using LOG / LOG comparison line chromatograms as seen in figure 6 below:
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Figure 6:
Trace level analysis and comparison. The Y axis in the upper part of the figure shows the concentration level, here in mole-% because we took a calibrated COMBINATION analysis. About “combined chromatograms” click “here”.
The concentration ranges at the Y-axis from middle down the figure has the same scale.
It is easy to see, that traces at the 100 ppb level could also be visualized. But as in figure 5 above the limits of trace level presentation is not a limitation of the LOG line chromatograms but mainly of the instrument hardware - see TEACHWARE.