Separation of Mixtures by Chromatography: RCS1601 Assignment Sample

Chemistry 1A 

1) Use the data obtained in Step (14) in Section 2.1 calculate the values of the three "known" compounds and each of the compounds in the "unknown" mixture. Ensure these values are all entered in Table 1 of the LRS. On the basis of these data determine the identity of each compound in the "unknown" mixture.

This is a lab experiment to be done using the apparatus provided. Hence it is NOT possible for me to address this question.

2) What are the two key objectives with which analytical chemistry is concerned and that can be achieved using gas chromatography?

The two primary goals of using gas chromatography is to for segregating and examining compounds that can be vaporized. Here there is no decomposition process involved .

3) What is gas chromatography (GC) used for?

Gas chromatography (GC) is a time tested model much more advanced when compared to the thin-layer or paper chromatography. The GC process helps to ascertain the quantum of each chemical present in the mixture about also its identification.

4) In GC, what is commonly used as the: (i) mobile phase and (ii) stationary phase?

In gas chromatography, the mobile phase (or "moving phase") is a carrier gas, normally an inert gas such as helium or an unreactive gas such as nitrogen.

The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, located inside a section of glass piece or metal tubing referred to as a column.

5) What determines the order in which each compound is eluted from a GC column?

The elution process is dependent on two key aspects:

• Boiling points of the solutes
• Reactions between the stationary phase the solutes and the stationary phase

The option of stationary phase not important if a mixture's components have different boiling points

It is an accepted fact that nonpolar solutes tend to get segregated in a quick manner.

The spectra will be similar throughout the peak’s elution if only a single component is contributing towards a peak in a chromatogram.

A minimum of two components are co-eluting if a spectrum at the starting of the peak’s elution is dissimilar from a spectrum taken near the closure of the peak’s elution.

6) What can be said about the retention time for a given compound run under a given set of experimental conditions in a GC instrument?

Retention time (RT) is defined as a measure of the time used by a solute to travel through a chromatography column. The data is computed as the duration from injection to detection.

The RT for a compound depends on many factors. This is despite the fact even if the same GC and column are utilized. The units used for retention times are seconds or minutes. The key parameters include: boiling point of the compound, solubility in the liquid phase and the temperature of the column.

7) Shown in Figure 3 is a schematic chromatogram.

8) With reference to Figure 3 answer the questions below and, where appropriate, give reasons for your answers.

The chromatogram is a two-dimensional chart. The ordinate axis illustrates concentration in terms of detector response. Whereas the abscissa indicates the time. The detector refers to the response as a peak. The h eight should be ideally dependent on concentration of the specific material.

a. How many different compounds are present in the chromatographed mixture?

Six different compounds

b. Which compound is present in the smallest amount?

Compound A is present in the smallest amount.

c. Which compound has the shortest retention time

Based on the definition of the retention time compound A has the shortest retention time.

d. Which compounds are present in equal amounts?

Compounds B and C are present in equal amounts

e. Which compound has the longest retention time?

Based on the definition of the retention time compound F has the shortest retention time.

f. Which compound is present in the greatest amount?

Using simple arithmetic compound F has the greatest amount .

g. Which compound has the greatest affinity for the stationary phase?

Compound F has the greatest affinity for the stationary phase since it has spent more time in the column.

h. Which compound has the greatest affinity for the mobile phase?

Compound A has the greatest affinity for the stationary phase based on the chromatography principles.

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