Identification of carbonyl compound from preparing its derivatives

1. A sample which is composed of many aldehydes and ketones,why it is inappropriate to use it directly to react with 2,4-dinitrophenylhydrazine to identify its component ?

2.Why using fractional distillation is not suitable for identification of its component?

3.What method is suitable to identify the given compound?

I don't know about the DNP mechanism.I know only that both of aldehyde and ketone are structual isomer and have reaction with 2,4-dinitrophenylhydrazine
to form2,4-dinitrophenylhydrazones. Is there anyone can help me?

Aldehydes and ketones react with a number of ammonia derivatives in weak acidic medium. these derivatives are crystalline solids with sharp melting and boiling points.
Aldehydes and ketones react with 2,4-Dinitrophenylhyddrazine to form 2,4-dinitrophenylhydrazones commonly known as DNP or Brady's reagent.

i think this should help.