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Partial separation of structurally similar organic acids at isocratic conditions

Small organic acids are an important group of chemical compounds that needs to be analysed and quantified in many different industries. This application shows ion chromatography of a variety of organic acids using a non-optimized isocratic carbonate-based eluent.

In the chromatogram of this application one can observe a distinct grouping of the acids into singly charged and doubly charged ions typically make separations of ions of different charges rather straightforward. In contrast can the task to achieve separation between ions of the same charge be a much more challenging task which may result in co-elution of compounds. The difference in retention of the carboxylic acids having the same charge illustrates how chemical characteristics such as hydrophilicity, hydrophobicity and molecular structure influence retention.

Organic acids chemical structures

Organic acids separation on a Shodex SI 50-4E column (250x4 mm) using an eluent containing 5 mM Na₂CO₃ and 5 mM NaHCO₃ in water pumped at 0.8 mL/min at 24 °C from an EQAX-B1 eluent bottle equipped with an EQAX-TC1 trap cartridge for carbon dioxide removal. Background reduced by XAMS suppressor with ASUREX-A100 automatic regenerator. Eluent pumping and conductivity detection by Shimadzu LC-10ADVP and CDD-10AVP, respectively. Injection of 20 µL of glycolic, propionic, pyrivic, malic, malonic, maleic, oxalic and fumaric acids (20-40 mg/L) in water.

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