Shown here is a schematic of a gas chromatograph in a pre-injection state. A 3 c

Question

Shown here is a schematic of a gas chromatograph in a pre-injection state. A 3 component mixture has been prepared for analysis.

1. Using the graphic template given, provide a modified graphical “snapshot” of what is taking place inside the GC and on the chart paper at the given time point below. For simplicity, use only one (1) sphere of each molecule.

Time Point - the moment just after the second component is detected:

2. Using the Molecular View of the column provided: a) draw 1 molecule of each analyte from part one (skeletal form) in the correct relative position in the column, and b) clearly show the relevant intermolecular forces that explain the column elution order.  

Please answer ALL components of the question and I will be sure to "thumbs up" your response!

Explanation / Answer

1. The three components in the mixture are propionitrile, iodomethane and piperidine. At the time point just after the second component is detected, the first component has completely eluted from the column. After detection by the detector, the peak corresponding to the first component is drawn by the chart recorder.

At the moment just after the second component is detected, a small portion of the second component has just reached the detector. So the remaining part of the second component is present at the end of the column (exit). The chart recorder just begins to draw the peak for the second component on the chart.

This is the snapshot of what is taking place inside GC and on the chart paper at the given time point.

2. The three components in the mixture are injected at the same time but they elute from the column at different times. This is because of the difference in polarities between them. The column contains polar adsorbent material. So a polar substance would interact more with the column than a non polar substance. Hence substances which are more polar would elute slowly while substances which are less polar would elute fast.

Of the given three components, propionitrile, iodomethane and piperidine, propionitrile is the most polar followed by iodomethane. Piperidine is the least polar of the three.

So, in the column, piperidine will elute first and propionitrile will elute last. The relative positions of the three components during elution will be as follows:

Piperidine – close to the exit.

Iodomethane – around the middle of the column

Propionitrile - at the beginning of the column

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