In this month's instalment, we examine long-distance running as a metaphor for gas chromatography (GC) separations. For those
readers who cannot stop thinking about work while on vacation, here is a light treatment of the separation process and a proposal
for a chromatography "fun run".
Summer is in full swing this month. Many chromatographers, myself included, look forward to participating in some of the plethora
of 10-km, half-marathon, or full-marathon long-distance running events offered worldwide. Besides the obvious benefits to
health and fitness, long-distance running offers opportunities for free-running thoughts that can turn the imagination to
musing upon seemingly disparate and otherwise unnoticed phenomena.
Long-distance runners often experience the sensation of travelling along a narrow passage — the "tunnel-vision" effect — with
reduced awareness of their surroundings beyond a few metres. This is a helpful adaptation of the senses that avoids undesirable
events such as tripping over a curb or colliding with the next runner ahead. For a chromatographer, a long-distance run can
be perceived as if moving through a flattened separation column. The race starts out with runners bunched tightly together
and finishes with runners distributed according to their abilities. At first glance, this result resembles a chromatography
separation, but how true is the likeness?
Long-distance runs and chromatography separations do share some attributes such as a long, narrow course and a chromatography
column; runners and solute molecules; segregation of runners into groups and the formation of discrete peaks; timing-chip
sensors and a chromatography detector; run completion times and retention times; an organized run start and an injection system.
Coincidentally, if the width of a long-distance race course is about 3 m then the length-to-width ratio of a 42.2 km marathon
course is similar to that of a 10 m × 0.75 mm gas chromatography (GC) column.
Some chromatography authors have remarked on the parallels between long-distance runs and a chromatography experiment (1,2).
The concept of a chromatography theoretical plate can be applied to the statistical distribution of runners finishing a race.
For example, the finishing times from a half marathon in 2012 had the distribution shown in Figure 1. The resemblance to a
tailing peak is unmistakable, but really this is just the statistical nature of two disparate processes as we will see shortly.
The finish-time distribution has the equivalent of about 40 total plates on the basis of the time of the distribution maximum
and its width at half-height. Blumberg (3) calculated that the 2001 New York City Marathon spread the runners into a distribution
with about 70 equivalent plates. Between these two races, the average plate height for a half to full marathon comes to about
560 m. Scaled down to the proportionately sized 10 m × 0.75 mm GC column, that is a plate height of about 130 mm — more than
two orders of magnitude larger (worse) than might be expected for this size GC column. I'd send that one back to the manufacturer
Figure 1: Distribution of finishers in a half marathon from 2012. Total number of runners = 2416; maximum Tmax occurs at 2.0 h; width at half-height wh ≈ 0.75 h; apparent plate number = 5.54 • (Tmax / wh)2 = 40.
Clearly, there are significant similarities and differences between chromatography and long-distance running. This article
examines the basic elements of a chromatography experiment — flow, diffusion, and retention — and imagines how a long-distance
race might be arranged to better represent chromatography. Along the way I will try to describe rules for a modified long-distance
chromatography "fun run" as a challenge to anyone who would like to try it out for a short distance, perhaps as a 5-km (3.1-mile)