Electrodialytic membrane suppressor for ion chromatography

TLDR: In this article, a dual membrane helical electrodialytic suppressor is described, where a platinum-wire-filled tube made of Naflon perfluorosulfonate membrane is coiled into a helix and a dc voltage is applied across the carbon bed and the platinum wire.

Abstract: A dual membrane helical electrodialytic suppressor is described. A platinum-wire-filled tube made of Naflon perfluorosulfonate membrane, inserted in another perfluorosulfonate membrane tube, is coiled into a helix. The helical assembly is inserted within an outer jacked packed with granular conductive carbon. An alkaline eluent, e.g., NaOH or Na/sub 2/CO/sub 3/, flows in the annular channel between the two membranes and pure water flows through the inner membrane and the outer jacket, countercurrent to the eluent flow. A dc voltage (typically 3-8 V) is applied across the carbon bed and the platinum wire. Na/sup +/ in the eluent migrates to the cathode compartment resulting in water as the suppressed effluent and NaOH as the catholyte effluent. The dual membrane design prevents direct electrode contact with the eluent; bubble induced noise in the suppressed eluent due to any residual gas is eliminated or minimized with a microporous gas-permeable membrane tube or by applying sufficient back pressure to the detectors exit. Up to 500 /mu/equiv of NaOH/min can be quantitatively suppressed with a membrane length of 50 cm and a band dispersion of 106 /mu/L (20-/mu/L sample). With typical eluents, the system permits detection limits in the low-parts-per-billion level for most common anions.