generic, pharmaceutical

Column screening using hydroxide gradients for ion chromatography method development

Hydroxide gradient elution is an effective approach in ion chromatography analysis due to its ability to separate organic acids and anions with a wide range of characteristics. During method development of such protocols, scouting gradients is a quick way to rapidly screen different columns and assess their potential for a certain analysis situation and sample composition.

Scouting gradients are designed to cover a wide range of eluent strengths within a single run, thereby enabling sufficient retention of early eluting compounds as well as ensuring proper flush out of strongly retained substances. This enables a quick way of screening several columns and assessing whether their interaction characteristics are sufficiently promising for further optimisation. The example below comes from a feasibility study at Diduco which screened ion chromatography columns for analysis of certain organic acids and anions present in a pharmaceutical formulation. The successful separation of the injected standards triggered further method optimization.

Hydroxide gradient ion chromatography separation of organic acids on an IonPac AS28-4µm column (150×4 mm) using an eluent containing 5-95 mM KOH in water pumped at 0.8 mL/min at 25 °C, continuously mixed online from two different EQAX-B1 eluent bottles (1 L), containing either ultrapure water or 0.1 M KOH eluent concentrate, both protected with EQAX-TC1 trap cartridges for carbon dioxide removal. Background reduced by XAMS suppressor with ASUREX-A200 automatic regenerator keeping the background increase <7 µS/cm from start to finish. Eluent pumping and conductivity detection by (Thermo) Dionex system with modules GS50, CD25, and LC30, connected to a Spark Holland Triathlon 900 autosampler. An IonPac ATC-HC trap column was used to trap anionic contaminants from the eluent, introducing a dwell time of 5 min for which the plotted gradient profile has been compensated. Injection of 20 µL of pyroglutamate, acetate, glycolate, gluconate, formate, chloride, malate, oxalate, fumarate (20 mg/L) in water.