Automated Programmable Preparation of Carbonate-Bicarbonate Eluents for Ion Chromatography with Pressurized Carbon Dioxide

Abstract

We introduce a novel carbonate-bicarbonate eluent generation system in which CO is introduced using programmable CO pressures across a membrane into a flowing solution of electrodialytically generated high purity KOH. Many different gradient types are possible, including situations where gradients are run both on the [KOH] and the CO pressure. The system is more versatile than current electrodialytic carbonate eluent generators and can easily generate significantly higher eluent concentrations (at least to 40 mM carbonate), paving the way for future higher capacity columns. Demonstrably purer carbonate-bicarbonate eluent systems are possible compared to manually prepared carbonate-bicarbonate eluents and with considerable savings in time. Performance in different modes is examined. The dissolved CO is removed by a carbon dioxide removal device prior to detection. Best case noise levels are within a factor of 2-3 of best case suppressed hydroxide eluent operation. The eluent system allows particular latitude in controlling elution order/time of polyprotic acid analytes. Although CO introduction is possible prior to hydroxide eluent generation, this configuration causes complications because of electroreduction of CO to formate.

A gas-free electrodialytic pH modifier for ion chromatography

“…Thus, the concentration calibration of carbonate solution cannot be directly carried out by conductivity measurement. Here it was performed by a suppressed IC method, in which either carbonate or bicarbonate can be normalized to be carbonic acid followed by measuring its conductance to establish the calibration curve of conductance and concentration [8]. Figure 1.…”

“…However, the main fraction of carbonate eluent is carbonate and the fraction of bicarbonate is less. For example, according to the method described previously [8], the ratio of bicarbonate/carbonate in potassium carbonate solution with concentration of 3 mM, 5 mM, 8 mM and 10 mM was measured to be 0.22, 0.18, 0.15 and Table 1. When no current was applied for the EPM, the ratio of bicarbonate/carbonate in different potassium carbonate solutions was less than 0.22.…”

Carbonic Acid Eluent Ion Chromatography

“…With water or KOH as the influent, we used the H 2 CO 3 or KHCO 3 −K 2 CO 3 formed for ion chromatography by exclusion (ICE) separations 1 or anion exchange chromatography with capabilities to program pH and concentration. 2 Removing CO 2 postsuppression is established with HCO 3 − − CO 3 2− eluents; 3 presently, with pure H 2 CO 3 eluents for ICE, it can also be removed postseparation. With improved CO 2 removal devices, 2 the detector influent is nearly pure water with only traces of H 2 CO 3 .…”

“…2 Removing CO 2 postsuppression is established with HCO 3 − − CO 3 2− eluents; 3 presently, with pure H 2 CO 3 eluents for ICE, it can also be removed postseparation. With improved CO 2 removal devices, 2 the detector influent is nearly pure water with only traces of H 2 CO 3 . The CO 2 introduction devices operate precisely obverse to degassers and are hence called engassers.…”

“…constructed as previously described. 1,2 The SSFM, based on two stainless steel frits (19 mm dia., 1 mm thick, 2 μm pores, www.idex.com), is shown schematically in Figure 1.…”