chromatogram
/ kroh-MAT-uh-gram /
Imagine standing at the finish line of a staggered race, clicking a stopwatch each time a runner crosses and noting how big the group is. Plot those clicks against time and you get a row of bumps — one for each batch of runners. A chromatogram is precisely that finish-line record for a chromatographic separation: a plot of what the detector sees as the components leave the column.
Formally, a chromatogram is the graph produced by a chromatographic run, showing the detector's response (the vertical axis) against time or eluted volume (the horizontal axis). Each separated component appears as a peak; the time at which a peak appears identifies which component it is, and the area under the peak reflects how much of that component was present.
It matters because the chromatogram is the actual readout of the whole analysis — from it a chemist reads identities, amounts, and the quality of the separation. Its honest caveat is that a chromatogram only shows what the detector can sense and what actually came off the column: a substance the detector is blind to, or one still stuck on the column, leaves no peak, so a clean-looking chromatogram is not by itself proof that nothing was missed.
Examining the chromatogram of a fuel sample, an analyst sees a tall peak at 4.2 minutes she knows is benzene and a smaller one at 6.8 minutes that should not be there, flagging a contaminant from its retention time and peak size.
The finished plot: peaks placed in time, their areas telling how much of each.
Confusingly, the same word once meant the developed plate or paper of early chromatography; today, in instrument work, it almost always means the detector-versus-time plot.