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Adsorption Isotherms I

Adsorption Isotherms I

Adsorption isotherms are mathematical models that describe how molecules in a gas or liquid phase interact with surfaces. Two of the most common isotherm models are the Langmuir and Freundlich isotherms, which relate to Type I monolayer chemisorption. The Langmuir model is based on four key assumptions:• Adsorption cannot exceed monolayer coverage.• All surface sites are equivalent.• Molecules adsorb only at vacant sites.• There are no interactions between adsorbed molecules.Consider the...

High-Performance Liquid Chromatography: Elution Process

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In High-Performance Liquid Chromatography (HPLC), the elution process is critical to the separation of analytes and the quality of chromatographic results. Elution describes how compounds move through the column and separate based on their interactions with the mobile and stationary phases. This process determines the resolution, peak shape, and retention times in the chromatogram, which are essential for identifying and quantifying components in complex mixtures. Understanding the elution...

Adsorption Isotherms II

Adsorption Isotherms II

Brunauer, Emmett, and Teller (BET) introduced a theory in 1938 that modified Langmuir's assumptions to explain multilayer physical adsorption. This theory is applicable to Type II isotherms and provides a more realistic picture of adsorption processes. The BET theory assumes a uniform solid surface with localized adsorption sites, where adsorption at one site doesn't affect adsorption at neighboring sites. This theory also allows for the possibility of additional molecules being adsorbed on top...

Analyte Adsorption and Distribution

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Adsorption of Gases on Solids

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Adsorption is a process where molecules, known as the adsorbates, accumulate on a surface, which is referred to as the adsorbent or substrate. Occurring at the solid-gas interface, this phenomenon is crucial in various scientific and industrial contexts. The reverse of adsorption is desorption.Two types of adsorptions exist: physical (physisorption) and chemical (chemisorption). Physisorption involves gas molecules held to the solid's surface by relatively weak intermolecular van der Waals...

Chromatography: Introduction

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Chromatography is a technique used to separate compounds based on differences of partitioning between two phases, the stationary phase and the mobile phase.
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Related Experiment Video

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Ion Exchange Chromatography (IEX) Coupled to Multi-angle Light Scattering (MALS) for Protein Separation and Characterization

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Injection technique for generating accurate adsorption isotherm data using the elution by characteristic points

Jörgen Samuelsson¹, Torgny Fornstedt

¹Department of Physical and Analytical Chemistry, BMC Box 577, SE-751 23 Uppsala, Sweden.

Analytical Chemistry

|September 11, 2008

Summary

The elution by characteristic points (ECP) method for determining adsorption isotherms can be inaccurate due to large injection volumes. A new "cut-injection" technique generates more accurate, nearly rectangular profiles, yielding reliable adsorption isotherm parameters.

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Published on: September 7, 2011

Area of Science:

Chromatography
Adsorption Science
Chemical Engineering

Background:

The elution by characteristic points (ECP) method is a rapid technique for determining adsorption isotherms.
Traditional ECP relies on overloaded elution profiles and assumes rectangular injection profiles.
Large injection volumes in classical ECP lead to significantly tailed injection profiles, violating method assumptions.

Purpose of the Study:

To address the errors in adsorption isotherm determination caused by non-ideal injection profiles in the ECP method.
To develop and validate a novel experimental injection technique for more accurate adsorption isotherm measurements.
To demonstrate the superiority of the new method over traditional ECP with full-loop injections.

Main Methods:

Development of a "cut-injection" technique to generate nearly rectangular injection profiles.
Application of the cut-injection method for acquiring adsorption isotherms.
Comparison of adsorption isotherms obtained by the cut-injection technique with those from accurate reference methods.

Main Results:

The traditional ECP method with full-loop injections introduces serious errors in determined adsorption isotherm parameters.
The newly developed cut-injection technique successfully generates nearly rectangular injection profiles.
Adsorption isotherms acquired using the cut-injection technique closely match those determined by accurate reference methods.

Conclusions:

The cut-injection technique significantly improves the accuracy of adsorption isotherm determination using the ECP method.
This novel injection method overcomes the limitations of classical full-loop injections.
The cut-injection technique provides a reliable and accurate alternative for studying adsorption phenomena.