Figure 1 shows chromatograms of single component standards of caffeine, sacchari

Question

Figure 1 shows chromatograms of single component standards of caffeine, saccharin, aspartame, and benzoic acid, run using the chromatographic conditions similar to those detailed in the experimental procedure. What is the elution order of the four components? Why? Chromatograms of single component standards of (a) caffeine (b) benzoic acid (c) aspartame and (d) saccharin obtained under similar conditions to those used in this experiment. The order of elution will be the same, but the retention times may be significantly different.

Explanation / Answer

By looking at the chromatograms given above, the elution order of the four standards is,

Eluted first : saccharin

Eluted second : caffeine

Eluted third : aspartame

Eluted last : benzoic acid

The compounds are eluted according to its affinity for the stationary phase and the mobile phase. Saccharin the most basic non-polar comes off the column first, followed by caffeine. Aspartame slightly more polar than caffeine gets eluted next and last is benzoic acid being the most polar gets eluted at the end. Benzoic acid stays longest on the column with strong interaction with the stationary phase.

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