---
title: "Ion Exchange and Electrophoretic Separations"
description: "Charged species need a separation that works on charge. Ion exchange holds them on an oppositely charged phase and releases them with a competing ion, while electrophoresis moves them through a gel or"
canonical: https://lightmysky.com/learn/science/ion-exchange-and-electrophoretic-separations-mt_6xaiivXbAd
source: https://lightmysky.com/learn/science/ion-exchange-and-electrophoretic-separations-mt_6xaiivXbAd.md
retrieved: 2026-09-12
---

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# Ion Exchange and Electrophoretic Separations

Charged species need a separation that works on charge. Ion exchange holds them on an oppositely charged phase and releases them with a competing ion, while electrophoresis moves them through a gel or a capillary under a field.

Subject: Science · Area: Chemistry · Ages 20 to 21
Page: https://lightmysky.com/learn/science/ion-exchange-and-electrophoretic-separations-mt_6xaiivXbAd

## Ready when they can

- Explains how an ion exchange resin retains an analyte and what an eluent competes for
- Predicts how changing pH changes the retention of a weak acid on an exchanger
- Explains what sets electrophoretic mobility and why size and charge both appear in it
- Describes how a suppressor makes conductivity detection possible in ion chromatography

## Lesson: Sorting charged species by charge

Ion exchange holds charged analytes on an oppositely charged phase and releases them with a competing ion. The column carries charged resin beads: a cation exchanger has negative beads that grip positive ions, while an anion exchanger has positive beads that grip negative ions. Bound ions are washed off by raising the salt level or shifting the pH, which disrupts the grip.

**Example.** Changing pH changes the charge of a weak acid and therefore its retention. At a pH where the acid loses its proton it turns negative and sticks to an anion exchanger; at a pH where it keeps its proton it stays neutral and washes through. So to predict binding, first work out the charge of each species at the given pH, then match it to the opposite resin.

Electrophoresis sorts by motion instead of sticking. Each charged molecule is pulled toward the oppositely charged electrode, and its speed depends on three things: size, shape, and net charge. Small highly charged molecules zip through the gel while big lightly charged ones lag. A suppressor then makes conductivity detection possible in ion chromatography by lowering the background signal of the eluent, so the analyte peaks stand out.

**Tip.** Two special cases remove one variable each. In SDS PAGE, soap like SDS unfolds proteins and coats them evenly negative, so charge per mass goes uniform and the gel sorts almost purely by size. In DNA gels every fragment already carries similar charge per mass, so short fragments outrun long ones through the mesh. Stain the bands and compare against a ladder of known sizes to read the result.

**Recap.** Opposite charges grip on the resin, fields pull by charge and size in gels, and the eluent or coating decides what remains.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Amino Acids and Peptides: Zwitterions and the Peptide Bond](https://lightmysky.com/learn/science/amino-acids-and-peptides-zwitterions-and-the-peptide-bond-mt_cXdg1yjq-n)
- [HPLC: Reversed Phase, Gradients and Method Development](https://lightmysky.com/learn/science/hplc-reversed-phase-gradients-and-method-development-mt_hlJl6nXQqT)

## Opens up

- [Mass Spectrometry: Ionisation Methods and Mass Analysers](https://lightmysky.com/learn/science/mass-spectrometry-ionisation-methods-and-mass-analysers-mt_JTTb7FM1L4)