The LC analyses were carried out using a mobile phase composed of acetonitrile, 2-propanol and water, under gradient elution.
Dansylated amines were separated on a Zorbax-XDB C18 column using a binary mobile phase composed of acetonitrile and 20 mmol L−1 ammonium formate, pH 5.5.
First, it was demonstrated that a classical mobile phase composed of CO2 methanol 90100 (v/v) was suitable to obtain great nebulization efficiency.
The chromatographic separation of OrA was accomplished by using a microbore anion-exchange column eluted with an isocratic mobile phase composed of 100 mM NaOH + 40 mM NaNO3.
A mobile phase composed of acetonitrile 0.2 M tetrabutylammonium hydrogen sulphate pH 6.5 0.2 M ethylenediaminetetraacetic acid pH 6.5 water (20:20:20:40; v/v/v/v) was used at a flow rate of 1 ml/min.
A Polaris® column with a C18-A stationary phase and a linear gradient mobile phase composed of a mixture of trifluoroacetic acid 1% (v/v) and acetonitrile allowed for optimal separation.
The optimized separation and detection conditions were accomplished by using a cation-exchange column eluted at 0.5 mL min−1 with an isocratic mobile phase composed of CH3CN and 25 mN H2SO4, 82/18 (v/v).
Chromatographic conditions were optimized using a central composite design, establishing the following optimal conditions: mobile phase composed by water: acetonitrile: acetic acid (50 50 0.3, v/v/v), flow rate of 1.20 mL/min and column temperature of 45°CC.
Analyses were performed within 3.5 min using RP C18 column in the isocratic elution mode with mobile phase composed of a mixture of 0.1% formic acid aqueous solution and 0.1% formic acid methanol solution (v/v; 79 21).
These derivatives were optimally separated with a C18 YMC-Pack ODS-A column set a 40 °C using a mobile phase composed of acetonitrile and water under gradient conditions.
Chromatographic separation of the analytes was successfully achieved on a Hypersil Gold (100 mm × 2.1 mm, 3 μm) using a mobile phase composed of acetonitrile water (30 70) containing 0.05% (v/v) formic acid.
