Effects of system peaks in ion-pair reversed-phase liquid chromatography for noscapine and metabolites.

System peaks were generated in an ion-pair reversed-phase system by co-injection of an alkylsulphate with the analytes. The acidic mobile phase contained acetonitrile and an aliphatic tertiary amine as a co-ion. The retention time of the system peak was regulated by the concentration and hydrophobicity of the co-ion and the alkylsulphate. The peak performance of the analytes was affected by co-elution with a system peak. Both peak distortions and improvements appeared, and the principles for the latter could be applied in a dual-column system involving trace enrichment and column switching.