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The utility of analytical chromatography depends on its ability to separate analytes, whether to identify or quantify them. Particularly in the latter case, peak areas must be defined with precision. Since many parameters affect the quality of results, there are a certain number of requirements regarding the resolution between solute peaks, the speed of analysis (elution time, then the time needed to return to the initial conditions of analysis if different from the final conditions), and even the column’s capacity (to avoid saturation). To do so, we often use software to simulate the separation by adjusting various physico‐chemical factors such as temperature, flow rate, and composition of the mobile phase.

Due to the various parameters interacting together, the chromatographer must always find a compromise between resolution, speed, and capacity, which we often represent with the image of a triangle whose corners correspond to these three opposing parameters (Figure 1.11). In any optimization, the goal is to ensure sufficient separation of the compound(s) of interest in a minimum amount of time. The resolution and the elution time are thus the two most important dependent variables to consider. However, chromatography is a slow type of analysis, since we have to wait for the elution of the most retained compounds and then for the column to return to the initial conditions before we can start the next analysis. If the resolution is very good, then optimization consists in saving time, for example by choosing a shorter column. Remember that resolution varies according to the square root of column length (see parameter N in Equation (1.35) and Figure 1.9).

Figure 1.11 The chromatographer’s compromise triangle between resolution, speed, and capacity. Any chromatographic analysis is subject to three contradictory criteria. If we favour one of these three criteria, the two others are necessarily disadvantaged. When we look for good selectivity, we must fall close to the resolution corner of this triangle. The shaded area indicates the domain corresponding to analytical chromatography based principally upon the five parameters K, N, k, α, and R.

Often, in a chromatographic assay, we are only interested in one or two compounds present in the sample. If we have a selective detector adapted to the analytes in question, we can facilitate the optimization stage, since the resulting chromatogram will be greatly simplified. In other cases, however, we try to separate the greatest possible number of compounds from the initial mixture.