A mixture of nonpolar compounds is separated by HPLC using an octyl (-(CH27CH3)

Question

A mixture of nonpolar compounds is separated by HPLC using an octyl (-(CH27CH3) stationary phase covalently bonded to the silica support. How would the retention times of the compounds change if the solvent composition was changed from 55 vol% acetone and 45 vol% water to 85 vol% acetone and 15 vol% water? O Increase Decrease O Not enough information O Remain the same A mixture of polar compounds is separated by HPLC using an amino (-(CH2)3NH2) stationary phase covalently bonded to the silica support. How would the retention times of the compounds change if the solvent composition was changed from 35 vol% acetonitrile and 65 vol% water to 70 vol% acetonitrile and 30 vol% water? O Not enough information Increase O Remain the same O Decrease

Explanation / Answer

Here C8 column is used, called as reverse phase chromatography. Hydrophobic support C8 has affinity for non polar molecules. Hence polar molecules will elute before nonpolar molecules . When non polar solvent is used, interaction of non polar molecule and solvent increaes and will be eluted. Non polar solvent should be used to elute non polar molecules.

In first question, when sovlent polarity is decreased, Non polar molecules will elute faster than with higher polar solvent system. So retention time Rt decreaes.

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