The following data for a mixture of hydrocarbons were obtained on a 25-m WCOT co
ID: 974420 • Letter: T
Question
The following data for a mixture of hydrocarbons were obtained on a 25-m WCOT column (0.25 mm i.d.) operated at 150EC. The liquid phase was SP-2100. The carrier gas flow rate was 30 mL/min
Compound
tr (min)
Peak Width (min)
Peak Area
Detector Response Factor
n-pentane
2.46
0.37
274000
0.630
n-heptane
4.47
0.41
761000
0.503
n-octane
6.53
0.43
319000
0.676
n-nonane
10.00
0.45
166000
0.618
a. Estimate the retention time for n-hexane.
b. Calculate the percentage of n-octane in this mixture.
c. Calculate the average number of theoretical plates for this column based on the data for n-pentane.
d. Calculate the resolution between n-heptane and n-octane. Is this resolution acceptable? Explain.
Compound
tr (min)
Peak Width (min)
Peak Area
Detector Response Factor
n-pentane
2.46
0.37
274000
0.630
n-heptane
4.47
0.41
761000
0.503
n-octane
6.53
0.43
319000
0.676
n-nonane
10.00
0.45
166000
0.618
Explanation / Answer
Answer
(a) around 3.5 minutes
(b)% of n-octane is 21.0%
(c)Theoretical plates for n-pentane is 707.3. where peak width is assumed which is equivalent to the peak width at 13.4 % of the peak height.
(d) 4.9 is resolution between n-heptane and n-octane. YES this much resolution is acceptable. Generally more than 1.0 resolution is acceptable in gas chromatography.
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