Fundamentals of HPLC 28 - Describing Eddy Diffusion

Summary

This video explains the concept of diffusion in chromatography, highlighting how molecules in a chromatographic peak follow different paths through the column, leading to band broadening. It discusses the trend of using smaller particle sizes in columns to reduce eddy diffusion and improve theoretical plate count, which helps in reducing band broadening. However, smaller particles result in higher resistance and increased back pressure. For columns with sub-2 micron particles, higher pressure pumps are required to manage this increased back pressure, balancing the benefits and challenges of these advanced chromatographic columns.

Takeaways

• 😀 Diffusion refers to the process where molecules in a chromatographic peak take different paths through the column, resulting in spread-out bands.
• 😀 Some molecules follow shorter paths through the column, while others take longer, 'scenic' routes, leading to band broadening.
• 😀 Band broadening is the result of these different paths, and it's a key factor affecting chromatographic efficiency.
• 😀 Recent trends in chromatography involve using columns with smaller particle sizes for packing.
• 😀 Smaller particle sizes in columns reduce the effect of eddy diffusion, which helps minimize band broadening.
• 😀 Columns with smaller particles lead to higher theoretical plate counts, improving separation efficiency.
• 😀 The trade-off with using smaller particles is that they increase column resistance, leading to higher back pressure.
• 😀 For longer columns with sub-2 micron particles, higher pressure pumps are required to manage the increased back pressure.
• 😀 The reduction in band broadening due to smaller particles results in better resolution and more precise measurements.
• 😀 The challenge with using smaller particles is that it demands more power to maintain the required flow rates due to the higher back pressure.

Q & A

What is diffusion in the context of chromatography?

Diffusion in chromatography refers to the process where molecules within the chromatographic peak take different routes through the column, leading to the spreading apart of the molecules, also known as band broadening.

What are the two types of paths that molecules can take through the column?

Molecules can take either the shortest path, referred to as the 'route to work,' or the longest path, which is described as the 'scenic route.'

What is the consequence of molecules taking different paths through the column?

The different paths that molecules take cause them to spread apart, resulting in band broadening, which affects the sharpness of the chromatographic peak.

How has recent chromatography technology evolved in terms of column packing?

Recent years have seen a trend toward using columns with smaller particle sizes in the packing material, which helps reduce band broadening and improve the theoretical plate count.

What is the effect of using smaller particle sizes in chromatography columns?

Smaller particle sizes reduce eddy diffusion, which leads to reduced band broadening and a higher theoretical plate count, enhancing separation efficiency.

What is the trade-off when using smaller particle sizes in chromatography columns?

The trade-off is that smaller particle size columns result in higher resistance, which generates increased back pressure, especially for longer columns with sub-2 micron particles.

What challenges arise when using columns with sub-2 micron particle sizes?

Columns with sub-2 micron particle sizes require higher pressure pumps to handle the increased back pressure generated during operation.

Why is it necessary to use higher pressure pumps for smaller particle size columns?

Smaller particle size columns have higher resistance, resulting in greater back pressure, which necessitates the use of higher pressure pumps to maintain effective flow and separation.

What is the benefit of using smaller particles in chromatography columns?

The benefit is that the reduced eddy diffusion results in better separation efficiency, leading to sharper peaks and a higher theoretical plate count.

What does band broadening mean in chromatography?

Band broadening refers to the spreading apart of the chromatographic peak as molecules travel through the column, caused by the different paths the molecules take and the resulting diffusion.