Chemistry: analytical and immunological testing – Including chromatography
Reexamination Certificate
1999-12-23
2001-11-13
Ludlow, Jan (Department: 1743)
Chemistry: analytical and immunological testing
Including chromatography
C436S150000, C073S061530, C073S061560, C204S551000, C204S647000, C205S335000, C210S656000, C210S662000, C210S670000
Reexamination Certificate
active
06316270
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for generation of a high purity acid or base particularly for use as a chromatography eluent.
In liquid chromatography, a sample containing a number of components to be separated is directed through a chromatography separator, typically an ion exchange resin bed. The components are separated on elution from the bed in a solution of eluent. One effective form of liquid chromatography is referred to as ion chromatography. In this known technique, ions to be detected in a sample solution are directed through the separator using an eluent containing an acid or base and thereafter to a suppressor, followed by detection, typically by an electrical conductivity detector. In the suppressor, the electrical conductivity of the electrolyte is suppressed but not that of the separated ions so the latter may be detected by the conductivity detector. This technique is described in detail in U.S. Pat. Nos. 3,897,213, 3,920,397, 3,925,019 and 3,956,559.
There is a general need for a convenient source of high purity acid or base for use, such as an eluent for liquid chromatography and, particularly, for ion chromatography. In one technique, described in U.S. Pat. No. 5,045,204, an impure acid or base is purified in an eluent generator while flowing through a source channel along a permselective ion exchange membrane which separates the source channel from a product channel. The membrane allows selective passage of cations or anions. An electrical potential is applied between the source channel and the product channel so that the anions or cations of the acid or base pass from the former to the latter to generate therein a base or acid with electrolytically generated hydroxide ions or hydronium ions, respectively. This system requires an aqueous stream of acid or base as a starting source or reservoir.
There is a particular need for a pure source of acid or base which can be generated at selected concentrations solely from an ion exchange bed without the necessity of an independent reservoir of an acid or base starting aqueous stream. There is a further need for such a system which can be continuously regenerated. Such need exists in chromatography, and specifically ion chromatography, as well as other analytical applications using acid or base such as in titration, flow injection analysis and the like.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and apparatus has been provided for generating acid or base in an aqueous stream, such as water alone or in combination with additives (e.g. ones which react with the acid or base or with the sample). The system provides an excellent source of high purity acid or base for use as an eluent for chromatography and, particularly, ion chromatography.
Referring first to a system in which a base is generated for anion chromatographic analysis, an aqueous stream is directed through a flowthrough cation exchange bed including exchangeable cations. An electrical potential is applied between an anode and a cathode in electrical communication with an inlet and an outlet portion of the bed, preferably near the inlet and outlet, respectively, of the bed. Cations on the bed electromigrate into the aqueous stream while hydroxide ions are electrolytically generated to form a base-containing eluent. A liquid sample stream containing anions to be detected together with the generated eluent flow through a chromatographic separator in which the anions are separated. The chromatographic effluent flows past a detector in which separated anions are detected. In one embodiment, between separation and detection, the separated anion stream flows through a flowthrough second cation exchange bed including exchangeable cations and hydronium ions with no electrical potential being applied. The second bed serves as a suppressor with hydronium ions in the bed being displaced by ion exchange with the cations of the base to convert the base to weakly ionized form for conductivity detection.
In a preferred embodiment, after completion of the desired number of cycles, flow through the first and second cation exchange beds is reversed by appropriate valving for the next sample stream. An electrical potential of the type described with respect to the first bed is applied to the second bed while the potential is discontinued in the first bed. Thus, the second bed generates eluent and the first bed suppresses conductivity of the base.
In another embodiment, the second cation exchange bed is disposed after the detector. In this instance, the second bed serves no suppression function. Instead, it serves as a sink or trap to retain the cations of the base and the eluent. By appropriate valving, flow may be reversed through the first and second beds with potential applied in the second bed but not the first bed. During the reversal setting of the valving, the second bed generates the base.
Since hydrogen and oxygen gases are generated in the ion exchange beds which could interfere with detection, it is preferable to pressurize the chromatographic effluent prior to detection, such as by use of a flow restrictor.
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Avdalovic Nebojsa
Liu Yan
Small Hamish
Brezner David J.
Dionex Corporation
Flehr Hohbach Test Albritton & Herbert LLP
Ludlow Jan
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