Topic: carbonate eluent

Carbonate-bicarbonate eluents are common to use when performing routine analysis of anions using ion chromatography (IC) with suppressed conductivity detection, most often in isocratic mode. These eluents contain bicarbonate (HCO₃^–) and carbonate (CO₃^2-) ions, plus sometimes also hydroxide (OH^–), at concentrations and ratios optimized to give suitable retention and selectivity for the studied anions on the column in use.

Eluent composition and preparation

As all liquid chromatography mobile phases, carbonate-bicarbonate eluents should be prepared from ultrapure water with 18.2 Mohm·cm resistivity. The table below contains some examples of carbonate-bicarbonate eluents and recipes for their preparation from pure anhydrous sodium salts. In addition, the table contains information about for which columns these are denoted as standard eluents by their manufacturers. It would also be possible to prepare stronger stock concentrate solutions and then dilute them to prepare the final eluent just before use, provided that they have not been contaminated by the bottle or environment during storage. An alternative approach is to purchase ready-made concentrate solutions of sodium bicarbonate and sodium carbonate in IC quality and dilute them to the desired concentrations before use.

Table of typical carbonate-bicarbonate eluents

Eluent	NaHCO₃	Na₂CO₃	NaOH*	Column**
1.7 mM bicarbonate 1.8 mM carbonate	0.286 g	0.382 g	–	Hamilton PRP-X110 ICSep AN1 ICSep AN300 IonPac AS4A-SC Shodex IC SI-90 4E
1.0 mM bicarbonate 3.2 mM carbonate	0.168 g	0.678 g	–	Metrosep A Supp 5 Shodex IC SI-50 4E
1.0 mM bicarbonate 3.5 mM carbonate	0.168 g	0.742 g	–	ICSep AN2 IonPac AS14
3.6 mM carbonate	–	0.763 g	–	Shodex IC SI-35 4D Shodex IC SI-52 4E
1.4 mM bicarbonate 4.5 mM carbonate	0.235 g	0.954 g	–	IonPac AS22
5.0 mM bicarbonate 5.0 mM carbonate	0.840 g	1.060 g	–	Metrosep A Supp 10
7.5 mM carbonate 0.75 mM hydroxide	–	1.590 g	0.120 g	Metrosep A Supp 16
Recipes for typical carbonate-bicarbonate eluents in 2.0 L ultrapure water (1994 g at 25 °C). Weight of 50% NaOH solution, stored protected from ambient carbon dioxide. *Indicating the standard eluent for each column as recommended by its manufacturer. Naturally, numerous other eluent compositions are possible to use with each column. Mentioning of a column do not constitute any endorsement or recommendation but may include a link to examples if available in the Diduco application database.

Protecting eluents from carbon dioxide

Note that all low-concentration high-pH eluents are sensitive to contamination by ambient carbon dioxide since this gas will form carbonate in solution, which thus change the properties of the eluent and make it stronger and reduce retention. This is most critical for hydroxide eluents, but also weak carbonate-bicarbonate suffers from this phenomenon. The effect can be avoided by protecting the eluent using an adsorbent (such as in Xenoic® EQAX-TC1 Trap Cartridge) that removes carbon dioxide from the incoming air during eluent withdrawal. The traditional approach was to sheet the eluent bottle with helium or nitrogen gas at low pressure, but this requires a more elaborate setup and larger investments to achieve similar results, and is not sustainable since helium is a non-renewable natural resource that easily escapes the atmosphere when released.

Learn more

To learn more, browse the application examples below or contact Diduco to discuss your specific analysis.

Applications

ion chromatography

Published case study of analytical quality by design method development and validation

Diduco has published a scientific peer-reviewed case study on how modern analytical method development can be performed in the pharmaceutical industry. The work was performed according to analytical quality by design (AQbD) principles to establish the design space and robust setpoint of the ion chromatography assay, and then validated according to the guidelines established by the International Council for Harmonization (ICH).

ion chromatography

Screening of contaminants and forced degradation products in lithium ion battery electrolyte

Electrolytes in rechargeable batteries for cars, mobile phones, and other portable electric devices typically contain negatively charged counterions that together with lithium and a non-aqueous solvent form an ionic liquid. The bis(fluorosulfonyl)imide anion is a rather new ionic liquid constituent which thus need new quality control procedures.

ion chromatography

Analysis of dietary supplement capsules with carnitine using a generic method for counterions

Oral L-carnitine is a dietary supplement that has been shown to reduce fatigue in elderly people with low muscular endurance, but its effects on athletes during physical activity are not well-supported. Although this endogenous compound is well-known for its involvement in the mitochondrial oxidation of long-chain fatty acids, no scientific evidence has been found that carnitine in isolation enhances fat-burning.

ion chromatography

Modernized assay for foscarnet following ICH guidelines

New preliminary assay for the antiviral medication foscarnet which is a DNA polymerase inhibitor that is used to combat herpes viruses, including drug-resistant cytomegalovirus, and to treat patients with HIV as part of salvage therapy. This method was developed by Diduco to meet the requirements in the ICH guidelines, as a contribution to the United States Pharmacopoeia initiative for modernized monograph methods.

ion chromatography

Quantification of common anions in bottled drinking water according to EPA method 300.1A

Official procedure for quality control of drinking water according to the United States Environmental Protection Agency. This procedure allows quantification of the seven common inorganic anions fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate in the ranges recommended by WHO and national authorities.

ion chromatography

Generic method for isocratic separation of fifteen common pharmaceutical counterions

Many medicines and dietary supplements are bases that carry a positive charge, and consequently these small molecules are accompanied by negatively charged counterions. Such anionic excipients may influence the properties of the pharmaceutical formulation and can also influence the effect of the active ingredient since different ion pairs can have different dissolution rates or abilities to penetrate cell walls.

ion chromatography

Analysis of dietary supplement capsules with glucosamine using a generic method for counterions

Oral glucosamine is a dietary supplement that is marketed to support the structure and function of joints and claimed to provide pain relief for people with arthritis and osteoarthritis, although there is no clear evidence that its benefit is significantly above placebo.

ion chromatography

Alternative method for determination of voriconazole impurity E

Voriconazole is an antifungal medication that is included on the WHO Model list of Essential Medicines. During synthesis of the active ingredient a resolving agent for chiral amines is often used, and it is thus necessary that the quality control prove that this substance is not present at harmful levels in the final product.

ion chromatography

Generic method for isocratic separation of ten common pharmaceutical counterions

ion chromatography

Quantification of common anions in drinking water according to EPA method 300.0A

Older version of the official procedure for quality control of drinking water according to the United States Environmental Protection Agency.

ion chromatography

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.

ion chromatography