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Preserving eluent quality with dedicated storage protected from ambient carbon dioxide

To ensure that liquid chromatography analysis methods meets regulatory demands of retention repeatability as dictated by pharmacopoeia and the ICH guidelines, it is important to protect weakly buffered eluents from ambient carbon dioxide. The formation of carbonate species will otherwise change the pH and strength of the eluent, thus shifting retention.

This experiment shows how quickly an ion chromatography hydroxide eluent may change if not protected appropriately. The data also shows how efficiently the EQAX-TC1 cartridge removes CO2 from incoming air, thus maintaining eluent quality during the use of this one litre eluent which was consumed within 30 hours from preparation.

Effect of EQAX-TC1 trap on retention time stability with hydroxide eluent

Retention time stability of four anion standards (fluoride, chloride, nitrite, nitrate) separated on a Shodex IC SI-90 4E column (250×4 mm) using an eluent containing 4 mM NaOH in ultrapure water, pumped at 1.0 mL/min at 25 °C from two different EQAX-B1 eluent bottles (1 L), either open to the air or equipped with an EQAX-TC1 trap cartridge for carbon dioxide removal. Background reduced by XAMS suppressor with ASUREX-A200 automatic regenerator. Eluent pumping and conductivity detection by a modular Metrohm system composed of 762 IC interface, 709 IC pump, 818 IC pump, 732 IC detector, 733 separation center. Eluent selection was alternating between the open and protected eluent bottle, respectively, allowing 60 min equilibration with each eluent followed by 30 min analysis, thus resulting in 3 hours between each injection with each eluent and less than 30 hours from start to finish of the experiment. Plotted eluent consumption was calculated at the time of each injection.

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