Читать книгу Chemical Analysis - Francis Rouessac - Страница 15

The chromatogram is a curve representing the variation over time of a parameter related to the concentration or quantity of the solute at the column outlet (Figure 1.3). Time (or very rarely the elution volume) is found on the horizontal axis, where the time origin coincides with the introduction of the sample in the injection system. The detector response is found on the vertical axis. The baseline corresponds to the detector response in the absence of any solute. The separation is complete between two compounds when the chromatogram shows two chromatographic peaks that start from and return to the baseline.

Figure 1.3 Chromatographic elution curve. Example of a graph of Eq. (1.1).

A component is characterized by its retention time t_R, which represents the time elapsed between sample introduction and the detection of its peak maximum on the chromatogram. In an ideal case, t_R is independent of the quantity injected. The longer the retention time, the wider the peak is.

A component that is not retained will elute out of the column at time t_M, called the hold‐up time or dead time ¹ (also designated t₀). The difference between the retention time and the hold‐up is referred to as the adjusted retention time of the compound t’_R.

In quantitative analysis, we often simply separate the mixture from the compound(s) to be assayed. If the signal sent by the sensor varies linearly with the concentration of a compound, then the same variation will occur for the area under the corresponding peak on the chromatogram.