1. What is HPLC Void Volume?

The void volume in HPLC represents the volume of mobile phase in the column that is not occupied by stationary phase. It's also known as the column dead volume or hold-up volume, and is crucial for method development and retention time calculations.

2. How Does the Calculator Work?

The calculator uses the void volume formula:

Where:

• \( r \) — Column radius (cm)
• \( L \) — Column length (cm)
• \( \epsilon \) — Column porosity (dimensionless, typically ~0.65 for packed columns)

Explanation: The formula calculates the geometric volume of the column and adjusts for the fraction of space occupied by mobile phase (porosity).

3. Importance of Void Volume Calculation

Details: Knowing the void volume is essential for determining retention factors (k'), calculating column efficiency (N), and scaling methods between different column dimensions.

4. Using the Calculator

Tips: Enter column radius and length in centimeters. Porosity is typically 0.65 for packed columns but can be measured experimentally if needed.

5. Frequently Asked Questions (FAQ)

Q1: What's the typical void volume for an HPLC column?
A: For a standard 4.6 × 150 mm column with ε=0.65, void volume is approximately 1.6 mL.

Q2: How does particle size affect void volume?
A: Particle size mainly affects porosity (ε). Smaller particles typically have slightly lower porosity (~0.6 vs ~0.7 for larger particles).

Q3: Is this the same as dead time?
A: No, dead time is void volume divided by flow rate. Void volume is a volume measurement (mL), dead time is temporal (minutes).

Q4: How accurate is this calculation?
A: It provides a good estimate, but actual void volume can vary based on packing quality and should be verified experimentally.

Q5: Does this apply to UHPLC columns?
A: Yes, the same formula applies, but UHPLC columns often have slightly different porosity values (typically 0.5-0.6).