Question

1. In this experiment we injected the sample to be analyzed by Gas Chromatograph equipped with an FID (Flame Ionization Detector). The detector ionizes the sample as it reaches it, and the peak is proportional to the number of ions with a live flame. Explain in detail, why we need to run a standard when the GC is equipped with an FID detector to identify the component in a sample?

2. Gas Chromatography is another chromatography method you are learning about this semester. Construct a table comparing and contrasting the two other chromatography methods (TLC and LC). Point out to differences and similarities between each method and the GC method. Give at least 4 criteria of comparison.

3. During last week’s lab of distillation, many of you had difficulties getting the fractional distillation column to work properly. Specifically, the liquid started condensing at the top of the fractional column and the vapor did not distill over. The lab instructor suggested that changing the bead size (which was in the column) to a larger size might improve the outcome of the experiment. Is this suggestion valid? Would it help the process or is this suggestion wrong? Explain your answer.

Answer 1

2 )

Techniques by physical state of mobile phase : it consist of two chromatography

1)GAS chromatography = as the name suggest is a separation technique in which the mobile phase is a gas .

separation is always carried out in a column . Packed columns are the routine work horses of gas chromatography, being cheaper and easier to use and often giving adequate performance.

2) Liquid chromatography (LC) = as the name suggest is a separation technique in which the mobile phase is a liquid. It can be carried out either in a column or a plane

Planar chromatography = it consist of Thin layer chromatography (TLC) Instead of using a stationary phase of paper, it involves a stationary phase of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat, inert substrate. Compared to paper, it has the advantage of faster runs, better separations, and the choice between different adsorbents. For even better resolution and to allow for quantification,

  TLC. . Useful for seperating and comparing mobility of solids and some liquids dissolved in the mobile phase by their affinities to the solid phase relative to the mobile phase.

GLC. The mobile phase ia s gas, the stationary phase is a liquid on a solid support. same concept as TLC. useful for seperating gases by their affinities to the stationary phase...the mobility can then be compared to known compounds for possible identification.

Thin layer chromatography and gas-liquid chromatography, as their names imply, are two types of chromatography. Both use two kinds of phases, the mobile phase and the stationary phase.

Aside from separating mixtures, both techniques can also determine the purity of the substance and identify a compound from the mixture.

The states of matter involved in both chromatographies are different when acting in the mobile and stationary phase. In thin layer chromatography, the mobile phase is a liquid while the stationary phase is a solid. In contrast, gas chromatography uses gas in the mobile phase and liquid in the stationary phase.

Another difference is the type of matter that the techniques can separate. In thin layer chromatography, the compounds are usually solids and some liquids. Meanwhile, gas-liquid chromatography separates gases.

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Doing a thin layer chromatography can be flexible. The important requirement is the thin-layer chromatography plate. Gas chromatography is more complex and requires the use of a special machine called a gas chromatograph. Gas chromatography uses a gas separator