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Method and apparatus for quantitative analysis of weakly ionized anions or cations
| Details |
Inventors: Rich, Jr., William E.; Johnson, Edward L.; Sidebottom, Thomas O.;
Assignee: Dionex Corporation (Sunnyvale, CA)
Primary Examiner: Marcus; Michael S.
Assistant Examiner:
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton & Herbert
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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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present method and apparatus are well adapted for the rapid and automated analysis of a mixture of weak anions (e.
g.
, organic carboxylates) or weak cations (e.
g.
, ammonia and organic amines) both being in aqueous solution containing up to the saturation limits of soluble metal halide and/or soluble strong (highly dissociated) metal hydroxide and/or strong (highly dissociated acid.
The determinable weak anions or cations include any of such compounds soluble enough to be present in the sample solution at a concentration at least equal to the detection limit of the conductivity cell, usually below about 20 parts per billion (ppb) of carboxylic acid or salt and below about 100 ppb of ammonia or amine.
As defined herein, "weak anions" are anions which, are poorly ionized in acid form, and which are resolved by ion exclusion chromatography in comparison to "strong anions" which are defined to be highly ionized in acid form, have a relatively low pK.
sub.
A value (e.
g.
, 0 to about 2) and which are not resolved by ion exclusion chromatography.
Strong and weak acids are defined to be acids of strong and weak anions, respectively.
As further defined herein, "weak cations" are cations which are poorly ionized in base form, and which are resolved by ion exclusion chromatography in comparison to "strong cations" which are defined to be highly ionized in base form, have a relatively high pK.
sub.
B value (e.
g.
, about 0 to 2), and which are not resolved by ion exclusion chromatography.
Strong and weak bases are defined to be bases of strong and weak cations, respectively.
Typical weak anions include mono- carboxylate groups (e.
g.
, formate and acetates), di- and tri-carboxylate groups, nitrite, alkyl sulfates, carbonate, alkyl sulfonate and their hydroxy and halogenated derivatives.
Typical strong anions includes strong mineral acids and specifically include halide, sulfate, chlorate, nitrate, sulfite, and chromate.
Typical weak cations include ammonia, primary, secondary and tertiary alkyl organic amines with less than 20 carbon atoms and alkyl diamines, triamines and some quarternary amines
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Liquid Purification 
