Question

What is the order of elution of the following compounds from a normal-phase packed HPLC column?

(a) ethyl acetate, acetic acid, dimethylamine

(b) propylene, hexane, benzene, dichlorobenzene

Short answer

(a) The order of the compounds is ethyl acetate, dimethyl amine and acetic acid.

(b) The order of the compounds is hexane, propylene, benzene and dichlorobenzene.

Step-by-step solution

Part (a) Step 1: Given Information

The order of the compounds from a normal-phase packed HPLC column is to be stated.

Part (a) Step 2: Explanation

The order of each compound depends on the polarity of the compounds. The compounds with more polarity will be placed at the last stage and vice versa. The acetic acid is most polar compound in the group and hence placed at the last stage in the group. The polarity of the dimethyl amine is lesser than the acetic acid and more than the ethyl acetate in the group. Therefore, the dimethyl amine will placed at the second last stage in the group. The ethyl acetate is placed at the first stage in group due to the lesser polarity. Hence, order is ethyl acetate, dimethyl amine and acetic acid.

Thus, the order of the compounds is ethyl acetate, dimethyl amine and acetic acid.

Part (b) Step 1: Given Information

The order of the compounds from a normal-phase packed HPLC column is to be stated.

Part (b) Step 2: Explanation

The order of each compound depends on the polarity of the compounds. The compounds with more polarity will placed at the last stage and vice versa. The dichlorobenzene is most polar compound in the group and hence placed at the last stage in the group. The polarity of the benzene is lesser than the dichlorobenzene and more than the hexane and propylene in the group. Therefore, the benzene will placed at the second last stage in the group. The polarity of the propylene is lesser than the benzene and more than the hexane in the group. Therefore, the propylene will placed at the third last stage in the group. The hexane is placed at the first stage in group due to the lesser polarity. Hence, order is hexane, propylene, benzene and dichlorobenzene.

Thus, the order of the compounds is hexane, propylene, benzene and dichlorobenzene.