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Diffusion on Chromatography Columns

Diffusion on Chromatography Columns

In column chromatography, when an analyte is introduced as a narrow band at the top of the column, the solutes begin to separate and broaden, developing a Gaussian profile. This broadening occurs due to various factors, such as longitudinal diffusion.
Longitudinal diffusion occurs when the solute molecules in the mobile phase diffuse from the more concentrated center of the chromatographic band to the more dilute regions on either side, both towards and against the flow direction. This...

Passive Diffusion: Overview and Kinetics

Passive Diffusion: Overview and Kinetics

Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting their diffusion into...

Diffusion

Diffusion

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...

Diffusion

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...

Drug Absorption Mechanism: Passive Membrane Transport

Drug Absorption Mechanism: Passive Membrane Transport

Passive transport is a method of drug absorption where small, lipid-soluble drugs can move across the cell membrane. This movement happens along the concentration gradient, which is a natural flow from higher to lower concentration areas. The speed at which the drug moves is directly related to its lipid–water partition coefficient. This means that the more a drug dissolves in lipids, the faster it diffuses or spreads throughout the body. It is important to note that most drugs are either weak...

Extraction: Partition and Distribution Coefficients

Extraction: Partition and Distribution Coefficients

The distribution law or Nernst's distribution law is the law that governs the distribution of a solute between two immiscible solvents. This law, also known as the partition law, states that if a solute is added to the mixture of two immiscible solvents at a constant temperature, the solute is distributed between the two solvents in such a way that the ratio of solute concentrations in the solvents remains constant at equilibrium.
For extracting a solute from an aqueous phase into an organic...

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Related Experiment Video

Updated: Jul 10, 2026

Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy

Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy

Published on: February 1, 2017

Diffusion coefficient depends on time, not on absorption.

Wei Cai, M Xu, Melvin Lax

|November 17, 2007

Summary

This summary is machine-generated.

The photon diffusion coefficient is independent of absorption but varies with time. After a long period, it stabilizes, supporting previous research on photon transport in scattering media.

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Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy

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Area of Science:

Optics and Photonics
Transport Phenomena
Applied Physics

Background:

The photon diffusion coefficient's dependence on absorption has been a subject of scientific debate.
Understanding photon transport is crucial in various fields, including medical imaging and material science.

Purpose of the Study:

To resolve the controversy regarding the photon diffusion coefficient's dependency on absorption.
To investigate the temporal behavior of the photon diffusion coefficient in a homogeneous scattering medium.

Main Methods:

Analytical solution of the photon transport equation.
Analysis of photon diffusion in an infinite homogeneous scattering medium.

Main Results:

The photon diffusion coefficient is independent of absorption.
The diffusion coefficient exhibits temporal dependence, decreasing at early times.
In the long-time limit, the diffusion coefficient approaches D=1/3μs(?), aligning with Furutsu and Yamada's findings.

Conclusions:

The photon diffusion coefficient is not directly dependent on the absorption coefficient.
Temporal dynamics play a significant role in photon diffusion, particularly at early stages.
The study provides a theoretical basis for photon transport modeling, independent of absorption effects.