A process for the alkylation of an aromatic substrate can include providing an alkylation reaction zone containing an alkylation catalyst, and introducing a feedstock including an aromatic substrate and an alkylating agent into an inlet of the alkylation reaction zone and into contact with the alkylation catalyst. The alkylation reaction zone can be operated at temperature and pressure conditions to cause alkylation of the aromatic substrate in the presence of the alkylation catalyst to produce an alkylation product including a mixture of the aromatic substrate and monoalkylated and polyalkylated aromatic components. The alkylation product can be withdrawn from the alkylation reaction zone. Nitrogen containing compounds in the aromatic substrate, alkylating agent, or both can be monitored in a range 15 wppb to 35 wppm by dry colorimetry. The process can include transalkylation of polyalkylated aromatic components in a transalkylation reaction zone containing a transalkylation catalyst.