2. In a chromatographic analysis of low-molecular-weight acids, butyric acid elu

Question

2. In a chromatographic analysis of low-molecular-weight acids, butyric acid elutes with a retention time of 7.63 min. The column’s void volume is 1.5 mL and the column was operated at a mobile phase flow rate of 5.0 mL/min. (Be careful with significant figures.) (1) What is the capacity factor for butyric acid? (2) In the same chromatographic analysis for low-molecular weight acids, the retention time for isobutyric acid is 5.98 min. What is the selectivity factor for isobutyric acid and butyric acid

Explanation / Answer

Void Time( tm ) = Column Void / Flow rate = 1.5 ml / 5.0 ml min-1 = 0.3 min

For Butyric acid

Capacity factor( Kbut) = (Retenction time - Void time)/void time = (7.63 min - 0.3 min)/0.3 min = 24.433

For isobutyric acid

Capacity factor( Kiso) = (Retenction time - Void time)/void time = (5.98 min - 0.3 min)/0.3 min = 18.93

selectivity factor = capacity factor of butyric acid/capacity factor of isobutyric acid = Kbut/Kiso

   = 24.433/18.93 = 1.29

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