Primesep mixed-mode columns are designed to separate basic, acidic, neutral and zwitter-ionic compound. Elution of these compounds is facilitated by acetonitrile and ions in the mobile phase. In all cases the retention time on mixed-mode columns is significantly longer than on traditional reverse-phase columns. Presence of cation-exchange mechanism in Primesep 100 column allows to achieve better retention and peak shape for analytes like phenylalanine and benzylamine. Various buffers can be used along with different detection techniques. This HPLC method can be adopted as a universal approach for analysis of basic, acidic and zwitter-ionic compounds in complex mixtures and formulations. Compounds can be monitored by UV, ELSD, CAD and LC/MS.

Mixture of polar acidic and basic compounds is separated on a Primesep AB mixed-mode HPLC column. Dopamine and tyrosine are retained by combination of reversed-phase and cation-exchange mechanisms. Maleic acid is retained by anion-exchange mechanism, and benzoic acid is retained by reversed-phase mechanism. Primesep AB is a trimodal column with a C12 hydrophobic chain and cation-exchange and anion exchange groups on the surface. Method utilizes UV detection but can be used with other detection techniques (ELSD, LC/MS, Corona).

Mixed-mode HPLC columns allow to analyze compounds with drastically different properties in one run. Acidic, basic, and neutral compounds can be separated in one run using either isocratic or gradient conditions. In this application, neutral hydrophilic (uracil, phenol and hydroquinone), neutral hydrophobic (toluene), hydrophilic acidic (benzoic acid), hydrophilic basic (lutidine) and hydrophobic basic (amitriptyline) are separated using gradient of ACN. Neutral compounds are retained by reversed-phase mechanism, hydrophilic acidic compound become more hydrophobic at lower pH and retain by reversed-phase mechanism too. Basic compounds are retained by cation exchange mechanism, and hydrophobic basic compounds are retained by reversed-phase and cation-exchange mechanisms. All compounds are resolved within 17 minutes on a short column. Method can be applied to various polar and hydrophobic compounds, which can be separated on one column and in one run. Mixed-mode columns can operate in single or combination of several modes: reversed-phase, ion-exchange, ion-exclusion and HILIC. This mixed-mode HPLC column can be used as a general column for separation of wide range of compounds.

Primesep 100 and Primesep 200 columns can be used as a universal column for analysis of wide range of compounds. These mixed-mode reversed-phase ion-exchange HPLC columns can provide a valuable alternative to traditional reversed-phase column. Amines, amino acids, quaternary amines, and various zwitter-ions can be analyzed along with hydrophobic compounds and organic and inorganic counter-ions. In this application, 8 compounds with different hydrophobic, hydrophilic, basic and acidic properties are separated based on their properties. Primesep 100 column is a mixed-mode HPLC column with a C12 carbon chain and carboxylic acid on the surface with pKa of 1. Primesep 200 column is a mixed-mode HPLC column with a C12 carbon chain and carboxylic acid on the surface with pKa of 2. These columns can be used with 100% organic (ACN) and 100% aqueous mobile phases. This HPLC method can be adopted as a generic and robust approach for analysis of acidic, basic and neutral compounds within the same run.

This application shows the effect of mobile phase composition on retention of acidic, basic and neutral compound. Retention of basic and acidic compounds is controlled by buffer pH and concentration, while retention of neutral compound is controlled by the amount of acetonitrile. Buffer pH changes not only ionization state of ionizable basic and acidic compounds, but ionization state of trimodal stationary phase Obelisc R. Available detection techniques include UV, ELSD, LC/MS, and Corona.