The Thermo Scientific™ Dionex™ Electrolytically Regenerated Desalter (ERD 500) replaces the Thermo Scientific Dionex Carbohydrate Membrane Desalter (CMD 300). The Dionex ERD 500 is designed with exterior hardware changes that allow the desalter to be more pressure tolerant than previous generation desalter devices.

The Dionex ERD 500 is designed to remove sodium ions (Na+) from the alkaline sodium acetate effluent after High pH Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC/PAD) oligosaccharide separations. The Dionex ERD 500 employs a countercurrent cation exchange mechanism (H+ exchanged for Na+) driven by both electrolytically generated and pneumatically supplied regenerant. Trifluoroacetic acid (TFA) should be used as the regenerant source for pneumatically supplied hydronium ions.

Typical oligosaccharide separations require 0 to 200 mM sodium acetate (NaOAc) in 50–100 mM NaOH. A properly operated Dionex ERD 500 will exchange ≥ 99.5 % of the sodium ions present (up to 0.35 M) under the desalting conditions provided in this manual.

Oligosaccharides eluting from Thermo Scientific Dionex CarboPac™ columns during HPAEC/PAD are detected prior to passage through the Dionex ERD 500, and elute from the Dionex ERD 500 in dilute acetic acid (HOAc). The pH of the alkaline eluent used for carbohydrate HPAEC/PAD is reduced from ~ 13 to between 2 and 6—depending on the eluent NaOAc concentration—after passage through an operating Dionex ERD 500.

Because HOAc is volatile, vacuum evaporation (e.g., in a centrifugal evaporator) will remove the HOAc leaving a dry oligosaccharide preparation, ready for further processing (such as, exoglycosidase treatment or mass-spectrometry).

WARNING

The Dionex ERD 500 will be damaged if power is supplied to the electrodes when regenerant is not supplied, and this will void the warranty.

Note that the Dionex ERD 500 may be used without supplying power to the electrodes but it is not recommended. Under these conditions, all of the exchange capacity is provided by the regenerant acid.

When only eluent is supplied (no power or regenerant flow supplied), the Dionex ERD 500 will continue to exchange H+ for Na+ until its exchange capacity is exhausted. At that point the conductivity and pH of the material eluting from the Dionex ERD 500 will be the same as that entering the Dionex ERD 500.

When the Dionex ERD 500 becomes exhausted, lowering or stopping the eluent flow (while continuing the regenerant flow) will decrease the time required for conversion of the cation-exchange membranes back to the H3O+ form.

See the following table for a list of suppressors covered in this guide.

Suppressor

Part Number

Dionex Electrolytically Regenerated Desalter ERD 500

Dionex ERD 500 (4 mm) Item # 085087

Dionex ERD 500 (2 mm) Item # 085089