Chromatography terminology — void volume In column liquid chromatography, the term “void volume” most commonly refers to which volume?

Introduction / Context:
Understanding void volume (often denoted Vm or V0) is important for calculating retention factors, estimating dead time, and interpreting unretained marker peaks in HPLC and other column methods.

Given Data / Assumptions:

• Packed columns contain solid particles (stationary phase) that displace volume.
• Mobile phase occupies the interstitial (interparticle) spaces that allow flow.
• Unretained compounds elute at roughly the void time corresponding to this volume.

Concept / Approach:
Void volume is the volume of mobile phase inside the packed bed that flows through the interparticle channels (and, for some modes like size-exclusion, corresponds to the volume outside porous beads). It is central to retention factor calculations: k = (tR − t0) / t0 where t0 is the void time.

Step-by-Step Solution:
Recognize that packing occupies part of the column volume.Define void volume as the volume available to the flowing liquid phase within the bed.Select the option that explicitly describes this interparticle eluent volume.

Verification / Alternative check:
Inject an unretained tracer (e.g., uracil in RP-HPLC) and compute V0 from t0 and flow rate; this matches the interparticle mobile-phase volume.

Why Other Options Are Wrong:
Option b includes reservoirs and tubing, which are outside the packed bed definition.Option c is a time, not a volume.Option d refers only to extra-column volume ahead of the column, not the bed's void volume.

Common Pitfalls:
Confusing extra-column volumes (mixers, tubing) with true column void volume; misusing t0 from poorly chosen unretained markers.

Final Answer:
The total volume of eluent (mobile phase) occupying the interparticle space in the packed column, the remainder being occupied by the packing material.