Name: ion exchange resins and charged molecules
Uploaded: 2024-04-04T10:51:25.000Z
Duration: 1 min 17 s
Channel: JoVE

L'échange d'ions sépare les molécules chargées d'une solution en les échangeant de manière réversible avec des ions mobiles, ou « actifs », associés à la phase stationnaire de charge opposée.
La phase stationnaire est généralement un solide poreux mais insoluble, comme les polymères organiques réticulés à haut poids moléculaire qui ont un grand nombre de monomères portant des groupes fonctionnels ioniques.
Les polymères anioniques avec des cations actifs sont des échangeurs de cations, tandis que les polymères cationiques avec des anions actifs sont des échangeurs d’anions.
Les échangeurs cationiques et anioniques sont en outre classés comme faibles et forts en fonction de leurs groupes fonctionnels.
Les ions mobiles attachés aux échangeurs d’ions migrent dans la solution et sont remplacés par les ions de charge similaire de la solution jusqu’à ce que l’équilibre soit atteint.
L’application de la loi d’action de masse à l’équilibre d’échange d’ions exprime le coefficient de sélectivité de la réaction.
Les échangeurs cationiques et anioniques épuisés sont régénérés en les lavant avec un excès de solutions acides ou basiques, respectivement.

Échange d'ions

Ion Exchange

La chromatographie par échange d'ions sépare les molécules chargées d'une solution en les échangeant de manière réversible avec des ions mobiles, ou « actifs », associés à la phase stationnaire de charge opposée. Cette méthode peut être utilisée pour séparer les ions, adoucir et désioniser l’eau et purifier les solutions. Les polymères composant la colonne échangeuse d'ions sont des polymères de poids moléculaire élevé et chimiquement stables, réticulés pour être poreux et essentiellement insolubles. Ils sont également fonctionnalisés avec des groupes acides ou basiques. Lorsqu'elles sont fonctionnalisées avec des groupes acides, les colonnes ou la résine sont appelées échangeurs de cations et contiennent des polymères chargés négativement avec des contre-ions positifs. Ceux-ci permettent aux cations d'être échangés à partir de la phase mobile. Lorsqu'elles sont fonctionnalisées avec des groupes basiques, les colonnes ou la résine sont connues sous le nom d'échangeurs d'anions, qui contiennent des polymères chargés positivement avec des contre-ions négatifs et échangent les anions de la solution.

Lors de l'échange d'ions, les contre-ions associés aux polymères en phase solide pénètrent dans la solution tandis que les ions de la solution interagissent avec le polymère à leur place. Notez que la capacité d’échange d’ions augmente à mesure que l’étendue de la réticulation augmente et que le nombre de groupes échangeurs d’ions augmente dans le polymère. Cet échange est réversible et se poursuit jusqu'à ce que l'équilibre soit établi.

Les échangeurs de cations acides peuvent être fonctionnalisés soit avec des acides forts, tels que l'acide sulfonique (−SO3H), présent dans l'acide polystyrène sulfonique, soit avec des acides faibles, tels que l'acide carboxylique (−COOH), présent dans l'acide poly(méthylméthylacrylique). De même, les échangeurs d’anions sont classés comme forts ou faibles. Les échangeurs d'anions forts contiennent souvent des groupes ammonium quaternaire (−CH2N(CH3)3+), comme ceux du chlorure d'ammonium quaternaire du polystyrène, et les échangeurs d'anions faibles sont souvent fonctionnalisés avec des amines substituées (−NH3+), comme celles de l'hydroxyde d'amine tertiaire du polystyrène.

L'échange d'ions sépare les molécules chargées d'une solution en les échangeant de manière réversible avec des ions mobiles, ou « actifs », associés à la ...

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Analytical Chemistry

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Introduction to Separation Methods

Introduction aux méthodes de séparation

KEY TERMS AND CONCEPTS

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ion exchange resins and charged molecules

Ion exchange chromatography separates charged molecules from a solution by swapping them with mobile, or active, ions on a stationary phase. It is used to separate ions, soften and deionize water, and purify solutions. The method depends on a solid column made of high-molecular-weight, chemically stable polymers that are crosslinked to make them porous and essentially insoluble.

These polymers are functionalized with either acidic or basic groups. When acidic groups are present, the resin is a cation exchanger. It has a negatively charged polymer with positive counterions, so it can exchange cations from the mobile phase.

When basic groups are present, the resin is an anion exchanger. It has a positively charged polymer with negative counterions, so it can exchange anions from the solution. During ion exchange, the counterions on the solid polymer move into the solution, and ions from the solution take their place.

The exchange is reversible and continues until equilibrium is reached. The ability to exchange ions increases when the polymer has more crosslinking and more ion-exchange groups. Cation exchangers can be strong or weak. Strong cation exchangers often use sulfonic acid groups, such as in polystyrene sulfonic acid, while weak cation exchangers often use carboxylic acid groups, such as in poly(methyl methylacrylic) acid.

Anion exchangers are also classified as strong or weak. Strong anion exchangers often contain quaternary ammonium groups, such as in polystyrene quaternary ammonium chloride. Weak anion exchangers are often functionalized with substituted amines, such as in polystyrene tertiary amine hydroxide.

Ion Exchange Resins and Charged Molecules

ion-exchange-resins-and-charged-molecules

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Ion exchange chromatography separates charged molecules from a solution by swapping them with mobile, or active, ions on a stationary phase. It is used to separate ions, soften and deionize water, and purify solutions. The method depends on a solid column made of high-molecular-weight, chemically stable polymers that are crosslinked to make them porous and essentially insoluble. These polymers are functionalized with either acidic or basic groups. When acidic groups are present, the resin is a...

key terms and concepts

Learn how ion exchange chromatography uses cation and anion exchangers to separate charged molecules, purify solutions, and soften water.

Ion Exchange Resins and Charged Molecules | JoVE K12

analytical chemistry

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Ion Exchange Resins and Charged Molecules

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