1. In this experiment we injected the sample to be analyzed by Gas Chromatograph
ID: 962669 • Letter: 1
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.
Explanation / Answer
1) FIDs use an air/hydrogen flame to pyrolyze the effluent sample. The pyrolysis of the compounds in the flame creates ions (destroy the sample). A voltage is applied across the flame and the resulting flow of ions is detected as a current. The number of ions produced, and therefore the resulting current, depends on the flame conditions and the identity of the molecule in question. (As a rough approximation, the current is proportional to the number of reduced carbons in the molecule.) In other words, the detector shows a different response to each compound. For this reason, separate calibrations (using a standard) must be performed for each compound analyzed.
2)
solid or liquid stationary phase.
equilibria physical adsorption.
Small amount of sample.
The stationary phase is in a solid support.
You can´t analyze patterns with samples simultaneously.
High Cost.
It is poorly reproducible.
A gas is used as mobile phase.
Solid stationary phase.
equilibria physical adsorption.
Small amount of sample.
The stationary phase is in a solid support
You can analyze patterns with samples simultaneously.
Low Cost.
It is reproducible.
A liquid is used as mobile phase.
Solid or liquid stationary phase.
equilibria physical adsorption.
Fast.
It requires an experienced operator.
Molecular weight limitation.
High power resolver.
Columns can be 10 to 30 meters.
Sensitive detectors.
Solid stationary phase.
equilibria physical adsorption.
Fast.
It requires an experienced operator.
No limitation of molecular weight.
Low power resolver.
Columns are 30 cm.
Less sensitive detectors.
3) This suggestion is wrong because if the beads are larger will be less gas-liquid equilibria and therefore separation at the outcome of the distillate will be lower. An improvement in the process would be decrease the size of the beads.
Chromatography Similarities Differences CGsolid or liquid stationary phase.
equilibria physical adsorption.
Small amount of sample.
The stationary phase is in a solid support.
You can´t analyze patterns with samples simultaneously.
High Cost.
It is poorly reproducible.
A gas is used as mobile phase.
TLCSolid stationary phase.
equilibria physical adsorption.
Small amount of sample.
The stationary phase is in a solid support
You can analyze patterns with samples simultaneously.
Low Cost.
It is reproducible.
A liquid is used as mobile phase.
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