Difference Between Rate Theory and Plate Theory

The key difference between rate theory and plate theory is that rate theory describes the properties of a chromatographic separation via comparing the rate of analyte eluted through the column, whereas plate theory describes the properties of chromatographic separation via determining the number of hypothetical plates in the column.

Both rate theory and plate theory are important in chromatographic analysis. These two theories describe the properties of moving analytes in the stationary phase of the chromatographic medium or the mobile phase.

CONTENTS

1. Overview and Key Difference
2. What is Rate Theory
3. What is Plate Theory 
4. Side by Side Comparison – Rate Theory vs Plate Theory  in Tabular Form
5. Summary

What is Rate Theory?

Rate theory is a concept in chemistry that describes the process of peak dispersion, and it provides an equation to calculate the variance per unit length of the column. This theory is very useful in column chromatography. Given below are some important characteristics of this theory:

• Rate theory provides a more realistic description of the processes that work inside a column
• It considers the time taken for the creation of the equilibrium between the stationary phase and the mobile phase
• It considers the effect of the rate of elution on the resulting ban shape or the chromatographic peak
• The mathematical expression is affected by the different paths that are available for the analyte to travel

Figure 01: Column Chromatography Technique

The rate theory gives an equation to determine the calculation of the variance per unit length of a column, in terms of the velocity of the mobile phase and properties of the analyte. The equation is as follows:

          H=σ²/L

Where H is the plate height, σ is the standard deviation of the band and L is the column length.

What is Plate Theory?

Plate theory is a concept in chemistry that describes the separation in a chromatographic technique in the form of hypothetical plates. This is a theory that is older compared to the rate theory of chromatography.

According to the plate theory, the chromatographic column is divided into a large number of hypothetical plates. The number of these imaginary segments is given as “N”. Here, we can assume that there is a complete equilibrium between the stationary phase and the mobile phase. From this theory, we can surmise that determine that a chromatographic column with a greater number of theoretical plates shows a greater separation and that a greater separation occurs when plate height is smaller.

Figure 02: Thin Layer Chromatography

We can determine the number of theoretical plates in the column via experimental methods such as examination of a chromatographic peak after elution by various methods; e.g. half-height method, USP method.

What is the Difference Between Rate Theory and Plate Theory?

Rate theory and plate theory are important in chromatographic separation techniques. The key difference between rate theory and plate theory is that rate theory describes the properties of a chromatographic separation via comparing the rate of analyte that elutes through the column, whereas plate theory describes the properties of chromatographic separation via determining the number of hypothetical plates in the column.

Moreover, rate theory provides a more realistic description of the processes that work inside a column, while plate theory provides a more hypothetical description of the same.

Below infographic summarizes the difference between rate theory and plate theory.

Summary – Rate Theory vs Plate Theory

Rate theory and plate theory are important in chromatographic separation techniques. The key difference between rate theory and plate theory is that rate theory describes the properties of a chromatographic separation via comparing the rate of analyte that elutes through the column whereas plate theory describes the properties of chromatographic separation via determining the number of hypothetical plates in the column.

Reference:

1. Hussain, Khalid. “Rate Theory.” LinkedIn SlideShare, 29 June 2012, Available here.
2. “Plate Theory.” Wikipedia, Wikimedia Foundation, 11 Mar. 2020, Available here.

Image Courtesy:

1. “Column chromatography sequence” By quantockgoblin – Own work (Public Domain) via Commons Wikimedia
2. “TLC black ink” By – Natrij at English Wikipedia. – Transferred from en.wikipedia to Commons (CC BY-SA 3.0) via Commons Wikimedia

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