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Combination apparatus and method for chromatographic separation and quantitative analysis of multiple ionic species
| Details |
Inventors: Rich, Jr., William E.; Smith, Frank C.; McNeill, Janet L.;
Assignee: Dionex Corporation (Sunnyvale, CA)
Primary Examiner: Marcus; Michael S.
Assistant Examiner:
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton & Herbert
Apparatus and method for chromatographic separation and quantitation of different ions of like charges in a sample, e.g., cations or anions. Referring to anion separation, the sample is directed to a first chromatographic column of the ion exclusion type in which the weak acids (e.g., carboxylic acids) and their salts are partially or totally resolved and separated from a fraction of strong acids (e.g., mineral acids) due to Donnan exclusion. The resolved weak acids may be passed directly to a conductivity cell for quantitative detection. The strong acids may be directed to anion exchange bed with a highly ionized developing reagent and eluted in resolved form with the effluent being passed to a suppressor ion exchange bed wherein the developing reagent is converted to a weakly ionized form without destroying the anion separation. Then, a fraction of the strong acids is detected with the same or a different conductivity cell. Prior to separation, the strong acids are preferably directed through a concentrator column formed of ion exchange resin in which they are retained but not resolved while the remaining solution is removed. Thereafter, the developing agent used for separation of the strong anion is passed through the concentrator column to remove the anions for resolution. The same technique can be employed for cations. In an alternative mode, the system is employed to separate and quantitate weak acids but not the strong ones. |
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DETAILED DESCRIPTION AND OBJECTS It is an object of the invention to provide a technique for the total quantitative analysis of strong and/or weak cations or anions in a sample solution.
It is a further object of the invention to provide a technique capable of such analysis at very low levels such as for use in water monitoring in connection with pollution control.
Further objects and features of the invention will be apparent from the following description taken in conjunction with the appended drawings.
In accordance with the above objects, a method and apparatus for chromatographic quantitation of a number of ionic species in a solution of all positive or negative charge is provided which includes the combined techniques of ion exclusion and ion chromatography.
Referring to the anion quantitation mode, the sample solution containing strong and weak acids is preferably directed through an ion exclusion resin column in the hydrogen form if water or other substantially ion-free solution is used as a developing reagent in which the strong acids or their salts are separated as a group in the resin void volume peak while the weak acids or their salts are resolved and subsequently eluted.
The weak acids may be passed directly to a conductivity cell for quantitation.
The strong acids may be passed with developing reagent through an ion exchange resin bed for chromatographic separation and elution.
Then, the solution of resolved strong acids is passed through another ion exchange resin bed in which the developing reagent is converted to a weakly ionized form or removed without disturbing the anion species separation and a stream is directed to a conductivity cell for quantitative detection.
In another embodiment, certain of the weak anions are further resolved and quantitated but the strong anions are not resolved.
An ion concentration column is preferably disposed between the ion exclusion column and the ion chromatography column and is of a type which retains the ionic species without resolving them
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