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Column Void Volume Equation:
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The column void volume (V₀) is the volume of mobile phase in a chromatography column that is outside of the particles. It represents the space between particles where the mobile phase can flow freely.
The calculator uses the void volume equation:
Where:
Explanation: The equation calculates the total geometric volume of the column and multiplies by the porosity factor to account for the space occupied by packing material.
Details: Knowing the void volume is essential for chromatography method development, determining retention times, and calculating column efficiency parameters.
Tips: Enter column radius and length in centimeters, and porosity as a unitless value between 0 and 1 (typically 0.3-0.4 for packed columns). All values must be positive numbers.
Q1: What is typical porosity for HPLC columns?
A: For well-packed HPLC columns, porosity is typically around 0.35-0.40 for totally porous particles and about 0.25 for core-shell particles.
Q2: How is void volume experimentally determined?
A: Void volume can be measured by injecting an unretained compound (like uracil for reversed-phase) and measuring its elution volume.
Q3: Does void volume change with mobile phase?
A: The geometric void volume remains constant, but the effective void volume may change slightly with mobile phase composition due to swelling of packing material.
Q4: What's the difference between total and interparticle porosity?
A: Total porosity includes both interparticle and intraparticle void volumes, while interparticle porosity only considers space between particles.
Q5: How does column packing affect void volume?
A: Poorly packed columns may have higher void volumes due to uneven packing and larger interparticle spaces.