What is the Difference Between Rate Theory and Plate Theory?
🆚 Go to Comparative Table 🆚Rate theory and plate theory are two important concepts in chromatographic analysis that describe the properties of moving analytes in the stationary phase. They differ in their approaches to understanding the separation process in chromatography:
Rate Theory:
- Provides a more realistic description of the processes that occur inside a chromatographic column.
- Focuses on the contributions of various kinetic factors to zone or band broadening.
- Takes into account phase properties, phase thickness, solute diffusivities, support size, support porosity, partition coefficients, and phase velocity.
- The van Deemter equation, which is derived from rate theory, is used to describe the relationship between these factors: $$H = A + B/u + Cu$$.
Plate Theory:
- Provides a more hypothetical description of the same processes.
- Conceptualizes the chromatographic column as a series of narrow, discrete sections called theoretical plates.
- Assumes that at each plate, equilibrium of the analyte is established between the mobile and stationary phases.
- The number of theoretical plates, N, is related to the height equivalent to a theoretical plate (HETP) by the following equation: $$n = LH = N$$, where n is the number of theoretical plates, L is the length of the column, and H is the effective plate height.
In summary, rate theory is a more realistic approach to understanding the separation process in chromatography, while plate theory is a more hypothetical approach. Plate theory focuses on the number of theoretical plates and their relationship to column efficiency, whereas rate theory considers the effects of various kinetic factors on zone or band broadening.
Comparative Table: Rate Theory vs Plate Theory
Here is a table comparing the differences between Rate Theory and Plate Theory in chromatographic analysis:
| Feature | Rate Theory | Plate Theory |
|---|---|---|
| Description | Describes the process of peak dispersion and provides an equation to calculate the variance per unit length of the column. | Provides a hypothetical description of the chromatographic column containing a large number of separate layers called theoretical plates, where separate equilibrations of the sample between the stationary and mobile phase occur. |
| Realism | More realistic description of the processes that work inside a column. | More hypothetical description of the processes that work inside a column. |
| Key Terms | Variance per unit length, peak dispersion. | Theoretical plates, height equivalent of a theoretical plate (HETP). |
| Column Efficiency | Describes column efficiency in terms of the variance per unit length. | Describes column efficiency in terms of the number of theoretical plates (N) and height equivalent of a theoretical plate (HETP). |
| Origin | Developed to describe the properties of moving analytes in chromatographic analysis. | Adapted from chromatography by Martin and Synge in 1941. |
Rate theory is a more realistic description of the processes inside a column, while plate theory provides a more hypothetical description. Both theories are important in chromatographic separation techniques, and they help understand the separation process and column efficiency.
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