Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2000-10-11
2003-05-06
Warden, Jill (Department: 1743)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S198200, C210S656000, C210S748080, C422S070000, C436S161000, C073S061520
Reexamination Certificate
active
06558551
ABSTRACT:
An Appendix consisting of 67 sheets is included in this application. The Appendix contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of any one of the sheets of the Appendix, as it appears in the Patent and Trademark patent files or records, but otherwise reserves all copyright rights to this material whatsoever. The pages of the Appendix are incorporated herein by reference as though fully set forth herein.
FIELD OF THE INVENTION
This invention relates to chromatography columns, apparatuses, and methods. In particular, the columns of the present invention can be used as the separation column in electroelution chromatography and are also adaptable for use as a self-regenerating suppressor in suppressed ion chromatography. The columns of the present invention may also be used to separate a wide range of compounds on both an analytical and preparative scale.
BACKGROUND OF THE INVENTION
A. Single Column Ion Chromatography
Single Column Ion Chromatography (SCIC) is a method of ion analysis in which ions are separated in an ion exchange column (e.g., separator column) and subsequently measured by a conductivity detector connected directly to the separator column. In SCIC, special ion exchange resins of low capacity, and eluants with either much higher or much lower equivalent conductance than the ions being measured must be employed. In ion chromatography, sample ions generate a signal at a conductivity detector. The signal is proportional to the sample ion concentration and is the difference in equivalent conductance between the sample ion and the eluant ion. SCIC sensitivity is limited by the difference in equivalent conductance between the sample ions and the eluant ions. This sensitivity is adequate and even preferred for some sample types, especially for cationic samples, where the difference in equivalent conductance between the sample and eluant ions is very large. However, for many other samples, particularly anionic samples, where the difference in equivalent conductance between the sample ions and eluant ions is small, sensitivity can be greatly increased by a second and preferred type of ion analysis called chemically suppressed ion chromatography (SIC).
B. Suppressed Ion Chromatography (SIC)
Suppressed ion chromatography (SIC) is a form of commonly practiced ion analysis characterized by the use of two ion-exchange columns in series followed by a flow through conductivity detector. The first column, called the separation column, separates the ions of an injected sample by elution of the sample through the column using an electrolyte as an eluant, i.e., usually dilute base or acid in deionized water. The second column, called the “suppressor” or “stripper”, serves two purposes. First, it lowers the background conductance of the eluant to reduce noise. Second, it enhances the overall conductance of the sample ions. The combination of these two factors significantly enhances the signal to noise ratio, thus increasing sensitivity.
This technique is described in more detail in U.S. Pat. Nos. 3,897,213, 3,920,397, 3,925,019 and 3,926,559. In addition, suitable ion exchange packings for the separation column are described in detail in U.S. Pat. Nos. 3,966,596, 4,101,460 and 4,119,580. A detailed description of ion chromatography is additionally provided in Small et al., “Proceedings of an International Conference on the Theory and Practice of Ion Exchange,” University of Cambridge, U.K., July, 1976; and also, Small et al., “Novel Ion Exchange Chromatographic Method Using Conductimetric Detection”, Analytical Chemistry, Vol. 47, No. 11, September 1975, pp. 1801 et seq. The foregoing patents and literature publications are fully incorporated herein by reference.
C. Gradient Elution Technology
To separate or elute sample ions retained on an ion-exchange column, an eluant containing co-ions of the same charge of the sample ions is routed through the separation column. The sample co-ions in the eluant partially displace the sample ions on the ion-exchange column, which cause the displaced sample ions to flow down the column along with the eluant. Typically, a dilute acid or base solution in deionized water is used as the eluant. The eluant is typically prepared in advance and routed through the column by either gravity or a pump.
Rather than using a homogenous eluant throughout the separation process, it is sometimes advantageous to use a gradient eluant, i.e., an eluant wherein the concentration of one or more components changes with time. Typically, the eluant starts at a weak eluting strength (e.g. a low concentration of the sample co-ions) and gets stronger (e.g. a higher concentration of the sample co-ions) during the separation process. In this way, easily eluted ions are separated during the weaker portion of the gradient, and ions that are more difficult to elute are separated during the stronger portion of the gradient. The eluant concentration changes during the gradient and suppressing or balancing the concurrent change in background conductance is required so the sample signal may be discriminated from the background signal. An example of such gradient elution techniques are disclosed in U.S. Pat. Nos. 4,751,189 and 5,132,018, the entire disclosures of which are incorporated herein by reference.
While the above patents utilize solutions prepared in advance to form a gradient eluant, U.S. Pat. No. 5,045,204 to Dasgupta et al. uses electrochemical methods to generate a high purity eluant stream that may flow directly to the separation column as it is produced, and which may be generated as a gradient. In the Dasgupta patent, a product channel is defined by two permselective membranes and is fed by a source of purified water. One of the permselective membranes only allows the passage of negatively charged hydroxide ions, which are generated on the side of this membrane opposite the product channel by the electrolysis of water at a cathode. The hydroxide ions are driven by an electric field through the membrane into the product channel in an amount corresponding to the strength of the electric field. The other permselective membrane only allows the passage of positively charged ions. On the side of this membrane opposite the product channel there is a source channel, which is continuously fed with a NaOH solution and in which an anode is positioned. The Na
+
ions are driven by the electric field through the membrane into the product channel in an amount corresponding to the strength of the electric field. By this process, a high purity sodium hydroxide (NaOH) solution is produced. This solution may be used as the eluant for a chromatography column, and the concentration of this eluant may be varied during the chromatographic separation by varying the strength of the electric field, thereby generating a gradient eluant.
The foregoing methods of elution ion chromatography suffer from certain disadvantages, however. Among these disadvantages is that an outside source of eluant or eluant counter-ions is required. Also, after eluting the sample ions from the chromatography column, all of these eluants require suppression in order to provide an accurate quantitative analysis of the sample ions. Finally, in general practice, all of the above methods of eluting are only applicable to one of either cation or anion sample ions within a single sample run. If one wishes to analyze both the cations and anions from a single sample, two chromatographic separations must be performed using either two apparatuses and two distinct eluants, or a single instrument with two or more columns and complex switching valves.
D. Prior Suppressor Technology
Chemical suppression for IC serves two purposes. First, it lowers the background conductance of the eluant to reduce baseline noise. Second, it enhances the overall conductance of the sample ions to increase the signal.
The combination of these two factors significantly enhances the signal-to-noise ratio, and increase the detectivity of the sample ions. For example, in
Anderson, Jr. James M.
Gerner Yuri E.
Saari-Nordhaus Raaidah
Sims Carl W.
Alltech Associates Inc.
Brinks Hofer Gilson & Lione
Starsiak Jr. John S.
Warden Jill
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