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Separation of organic acids by ion-exclusion chromatography

Separation of organic acids can be a challenging task due to their hydrophilic nature and structural diversity. One of the more traditional approaches to this analysis is ion exclusion chromatography, which offer complementary selectivity to other separation techniques, especially for the monovalent acids which tend to be more strongly retained in this mode.

This example shows an attempted separation of twelve organic acids during a column screening where several of the analytes were of relevance to a product development project within the pharmaceutical industry. Changing the concentration of the eluent did not increase resolution for this set of analytes on this column. Addition of low amounts of organic solvents such as methanol or acetonitrile to this eluent reduced retention of all acids and did not improve the separation.

Separation of twelve organic acids by ion exclusion chromatography

Separation of 12 organic acids by ion-exclusion chromatography on an IonPac ICE-AS6 column (250×9 mm) using an eluent containing 0.7 mM hexafluorobutyric acid (HFBA) in water, pumped at 1.0 mL/min at 25 °C. Background reduced by Dionex AMMS-ICE 300 suppressor regenerated by 5 mM tetrabutylammonium hydroxide (TBAOH) delivered at 4 mL/min. Pumping of eluent and regenerant, plus conductivity detection performed by Metrohm 761 Compact IC. Injection of 50 µL of oxalic acid (1), maleic acid (2), glyoxylic acid (3), malonic acid (4), malic acid (5), glycolic acid (6), formic acid (7), lactic acid (8), acetic acid (9), succinic acid (10), fumaric acid (11), acrylic acid (12), at 5-50 mg/L in eluent, giving signals of 1-12 µS/cm.

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