= Extracted ion profile
An \b[extracted ion profile] plots selected <mass-to-charge ratio> signal across a time-ordered series of <mass spectra>. The selection can be one value or a set of values. When time follows a chromatographic separation, the result is an <extracted ion chromatogram>; the broader profile term also covers other time-dependent sampling.<Extracted ion profile in IUPAC Gold Book>[Entry12410, definition and sampling examples.]{ref}
For recorded spectra $I_k(t_j)$, an explicit <extracted ion mass window> $W$ gives the reconstructed trace
$$
E_W(t_j)=\sum_{k\in W}I_k(t_j).
$$
This selects information already present in the spectra. It does not create missing mass measurements or turn the acquisition into a different instrumental measurement. Unlike a <total ion current profile>, it excludes signal outside the stated window.
An original three-scan example shows how the window changes the result. At mass coordinates $499.98$, $500.00$ and $500.03$, let the intensity vectors be $(0,1,0)$, $(3,8,5)$ and $(0,2,10)$ at successive times. A window $500.00\pm0.01$ selects only the middle coordinate and gives $(1,8,2)$. Widening to $500.00\pm0.04$ includes all three coordinates and gives $(1,16,12)$. The larger late signal in the broad trace comes from added spectral content; it is not evidence that the middle-coordinate signal remained high.
Choosing a window requires considering <mass resolving power>, mass-coordinate accuracy and what the instrument actually recorded. A narrow window can exclude a shifted target peak; a wide window can include neighbors. Even an isolated mass coordinate need not identify a unique chemical species, because different ions can share it. Preserve the raw spectra and state the window, summation rule and time axis so the profile can be reproduced and interpreted.
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