IC Accessories

Model Number

CI SAMS

The SeQuant Anion Membrane Suppressor (SAMS™ is a high performance suppressor for Ion Chromatography (IC). It provides a high capacity chemically regenerated membrane suppressor that through an ion exchange based neutralisation reaction converts anion chromatographic eluents to their corresponding low conducting acids (carbonic acid, water). It thereby reduces the background conductivity and increases the sensitivity for the analyte anions, that are converted to their corresponding strong acids (e.g., hydrochloric acid).

SAMS-enables, according to a proven principle, a continuous high capacity suppression and due to its unique design, the bandbroadening is kept at a minimum. It can be installed in practically all IC systems used today and in combination with the SeQuant Continuous Regeneration System (CARS™) a continuous suppression is obtained without the need for complicated electrochemical devices or the handling of large volumes of sulphuric acid.

The SeQuant Anion Membrane Suppressor (SAMS- operates according to a robust and proven principle. It was introduced in Sweden 1987 and it is nowadays in widespread use and known for providing a low and quiet background conductivity baseline in the analysis of common anions.

THE SUPPRESSOR REACTION

Detection in Ion Chromatography is mostly carried out by measuring the electrolytic conductivity, since this property is shared by all ions. In suppressed anion chromatography the eluent contains a relatively high amount of a salt corresponding to a weak acid (carbonate buffer, hydroxide). By that it has a high conductivity. In the suppressor the conductivity of the eluent is reduced by an ion exchange neutralisation reaction across the membrane and the salt of the weak acid is converted to its undissociated acid form (carbonic acid, water), that has low conductivity. The analytes suitable for suppressed anion chromatography are typically salts corresponding to strong acids and the conductivity of these are enhanced by the suppressor reaction.

FIGURE 1: Schematic drawing of the ion exchange process in a membrane based anion suppressor.

In SAMS-the eluent flows inside of a tubular membrane, while the acid regenerant flows on the outside in the opposite direction. Optimal performance is achieved when the regenerant acid concentration is kept low (typically 5-20 mM) and the flow rate high (typically 5-20 mL/min). During separation of anions with an alkaline eluent cations are exchanged through the membrane, i.e. Na+ or K+ from the eluent is exchanged to H+ from the regenerant acid. The transport through the membrane is conducted by covalently bonded sulphonic acid groups in the membrane, that selectively transport the cations. Electrostatic repulsion caused by Donnan exclusion prevents the anions in the eluate (i.e., OH-, HCO3-/CO32- and the sample ions) and in the regenerant, from passing through the membrane.

No ion exchange membranes work ideally and a small part of the regenerant (< 0.1%) may therefore pass the membrane if an inorganic acid like, e.g., sulphuric acid is used as regenerant. To obtain an extremely stable background and to avoid changing acid in the regenerant channel, SeQuant offers a continuous regeneration system, CARS.

A typical carbonate buffer eluent containing 2.4 mM Na2CO3/3.0 mM NaHCO3 usually result in a background conductivity of 15-20 cm-1 and a pH around 4 after the suppressor. A hydroxide eluent containing 10 mM NaOH usually give a background conductivity of 1-4 cm-1 and a pH between 5 and 6. With CARS the background is generally even lower. These figures presume that the eluents have been prepared from high quality deionised water and precautions to avoid contamination.

FIGURE 2: The composition of carbonate and hydrogen carbonate in a 5 mM carbonate eluent at different pH. The dot in the drawing marks the point of intersection for HCO3and H+, where the pH of the eluate is expected if the suppressor membrane behaves ideally.

 

FIGURE 3. Ion exchange in a SeQuant SAMS-connected to SeQuant CARS-for continuous regeneration.

TECHNICAL INFORMATION

The exceptionally stable polymer membrane tube ensures a long lifetime. Through its knitted design, the membrane tube forms a tortous flow path where an efficient radial mixing and high surface-to-volume ratio ensure a high suppression efficiency with minimal band-broadening.

The suppressor housing is manufactured from inert PVDF and the end-pieces are made from chemically resistant PEEK to fit standard 10-32-UNF or -- 28 UNF flatbottom plastic fittings for 1/16" tubing. A complete fitting kit is supplied with the suppressor.

Each suppressor is individually tested and supplied with a protocol in the delivery, together with a comprehensive set of guidelines for its use.