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.

Parabens are common preservatives in pharmaceutical and cosmetic industries. They are esters of p-hydroxybenzoic acid. Method for separation of methyl paraben, propyl paraben, benzonitrile and toluene was developed on a Obelisc R column. All four compounds are neutral and are retained by reverse-phase mechanism. In case of reversed-phase stationary phase, no effect of pH is observed. Retention time for all four compounds changes on an Obelisc R column when pH is changed. pH of the mobile phase affects ionization state of stationary phase. Obelisc R column has C12 carbon chain and carboxylic acid with pKa of 4. At lower pH (pH 2, TFA), carboxylic acid of stationary phase is not ionized and thus adds hydrophobicity to stationary phase. Obelisc R column can be used for analysis of basic, acidic and neutral compounds with suitable detection techniques - UV, ELSD, CAD, LC/MS.