Dionex Corporation

Edward L Johnson

Christopher A Pohl

Rosanne Williamson Slingsby

William E Rich, Jr

Thomas O Sidebottom

Leilani Angers

a method of ion analysis and detection of weakly dissociated anions or cations in an eluent by first separating such ions on a chromatographic separation medium by ion exclusion chromatography or mobile phase ion exclusion chromatography. The eluent include an acid or base with a co-ion of the same charge as the ions to be separated, such co-ions being in the hydronium or hydroxide form. In one embodiment the effluent from the separation medium is contacted with one side of an ion-exchange membrane having exchangeable ions of opposite charge to the ionic species. The opposite side of the membrane includes a regenerant with salt-forming suppression ions capable of forming a weakly conducting salt with the co-ions. Then the separated ionic species are detected preferably by a conductivity detector. In another embodiment, the membrane is replaced by a resin bed with ion-exchanging sites of opposite charge to the co-ions. There, co-ions form a suppressed salt with the exchangeable ions.

Method and apparatus for ion analysis and detection using reverse mode

Method and apparatus for quantitative analysis of weakly ionized anions (e.g. carboxylates) or cations (e.g., organic amines). For anion analysis, the sample and a strong acid (e.g., HCl) eluent are passed through an ion exclusion chromatography column (cation exchange resin) to resolve the weak anions while eluting the strong anions in the void volume peak. HCl is stripped on an ion exchange stripper column in the silver ion form and the effluent is directed through a conductivity cell and associated readout for detection. For weak cation analysis, the sample and a strong base (e.g., Ba(OH).sub.2) eluent are passed through an ion exclusion chromatography column (anion exchange resin) to resolve the weak cations while eluting the strong cations (e.g., Na.sup.+, K.sup.+) in the void volume peak. Ba(OH).sub.2 is stripped on an ion exchange stripper column in the sulfate ion form and the effluent is directed through a conductivity cell and associated readout for detection.

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Milpitas, CA, United States of America

Edward L Johnson