answer the question below 6,7,8 Why is it important that the temperature of the
ID: 1063112 • Letter: A
Question
answer the question below 6,7,8
Why is it important that the temperature of the column oven in a gas chromatograph be above the dew point of the least volatile component in the sample? A gas chromatogram shows a "peak" for each component present in the sample mixture. What is the area under each "peak" proportional to? Two of the most important instrument parameters that affect separations in gas chromatography are: (1) carrier gas flow rate, and (2) column temperature. How would the separation of components in a mixture using GC be affected if the carrier gas flow rate is (1) too fast, or (2) too slow? Explain your reasoning. How would the separation of components in a mixture using GC be affected if the column temperature is (1) too high, or (2) too low? Explain your reasoning. How are the retention times of the components in a sample mixture determined in gas chromatography? Separation of substances by GC can be based on differences in what three molecular properties?Explanation / Answer
6.
The column temperature has to be above the dew point of the less volatile component in the sample to prevent condensation in the column.
7)
The area under each peak is proportional to the amount of substance in a sample. However, the proportionality constant is different for each substance and detector. Therefore, to do quantitative analysis by gas chromatography, it is necessary to determine the proportionality constant for each substance in the sample.
Once we know the RF for target analyte we can determine the concentration of that analyte in sample by getting the peak area. Concentration (C) = RF x A
Here A is the area under each peak.
8)
a)i. A high flow rate produces sharp peaks, but a poor separation.
ii. A very slow flow rate leads to significant peak broadening and causes a bad separation due to increased overlap of peaks.
b) The column temperature has to be above the dew points of the compounds to prevent condensation in the column.
b. The temperature of the oven can be gradually be changed to provides a better result due to the fact that the differences in boiling points can additionally be used to separate the compounds. The separation is greatly improved, the peaks are less broad, and the higher boiling components leave the column much earlier.
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