= Extracted ion chromatogram
An \b[extracted ion chromatogram] is an <extracted ion profile> whose time axis follows a chromatographic separation. A <mass spectrometer> records successive <mass spectra> as separated material reaches the ion source; software follows a chosen <mass-to-charge ratio> interval through those spectra. It is a selected view of the recorded data rather than a direct picture of a single chemical species.<Extracted ion profile in IUPAC Gold Book>[Entry12410, selected mass/time profile and chromatographic example.]{ref}
The apparatus supplies two kinds of discrimination: chromatography changes when material reaches the detector, while mass analysis distinguishes ion coordinates at each time. An <extracted ion mass window> specifies which recorded coordinates contribute. A narrow window cannot separate two coeluting species whose relevant ions occupy the same mass coordinate.
An <extracted-ion chromatogram peak area> integrates selected signal over an explicitly chosen time range. For original sample points $(t,E)=(0,0),(1,4),(3,0)$, in minutes and arbitrary signal units, straight-line interpolation gives
$$
\int_0^3E(t)\,dt\approx\frac{0+4}{2}(1)+\frac{4+0}{2}(2)
=6\,\text{signal units}\cdot\mathrm{min}.
$$
The unweighted sum of ordinates is4, which ignores the unequal time intervals. These stipulated data illustrate numerical integration, not an experimental chromatogram.
Peak height and area also answer different questions. Triangular model peaks with height5 and full base widths2 and4 minutes have areas5 and10 signal-unit minutes. The same peak height does not imply the same integrated response. Converting area to amount requires an appropriate calibration and response model.
State the mass window, acquisition time spacing, baseline and time boundaries. Changes in baseline or overlap can change assigned area without changing analyte amount. Comparing retention behavior and other chemical evidence helps interpret a selected trace; its apparent isolation alone does not establish identity or freedom from <analytical matrix effects>.
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