Why is it difficult to prepare pure amines by ammonolysis of alkyl halides?

Explanation

By ammonolysis of alkyl halides, a mixture of primary, secondary and tertiary amines is formed.
`NH_(3) overset(RX)(to) underset(1^(@)"Amine")(R-NH_(2)) overset(RX)(to) underset(2^(@)"Amine")(R_(2)NH) overset(RX)(to) underset(3^(@)"Amine")(R_(3)N) overset(RX)(to) underset("Quaternary salt")(R_(4)N^(+)X^(-))`
The separation of these amines is very difficult. Thus, it is very difficult to prepare pure amines by ammonolysis of alkyl halides.