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An 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.^[ref]

For recorded spectra $I_k(t_j)$, an explicit extracted ion mass window $W$ gives the reconstructed traceThis 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 $500.00\pm 0.01$ selects only the middle coordinate and gives $(1,8,2)$. Widening to $500.00\pm 0.04$ 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.

Total ion current is a sum of ion currents in mass spectrometry, with an important distinction about where it is measured. After mass analysis, it is the sum of separate ion currents contributing to the mass spectrum, sometimes called reconstructed ion current. Before mass analysis, it can mean the sum of all same-sign ion currents. A reconstructed total over a selected analyzer range need not include every ion initially produced.^[ref]

For discretely recorded spectral intensities $I_k$, a corresponding reconstructed signal is $S={\sum }_{k\in K}{I}_k$, where $K$ specifies the included mass-to-charge ratio bins. Instruments may store intensities in arbitrary response units or counts rather than amperes, so the reported total needs its acquisition convention. Equal-bin sums and integrals of intensity density also require different bin-width bookkeeping.

For an invented three-bin example, spectra $(4,6,0)$ and $(1,1,8)$ both have total $10$. The total alone cannot distinguish their different ionic compositions. If acquisition excludes the third bin, the two reconstructed totals become $10$ and $2$ without any change in the stipulated source outputs. A changing measurement range can thus change the reported total.

Plotting reconstructed totals from successive spectra against time gives a total ion current profile; in coupled liquid chromatography, this can display when substantial summed signal reaches the detector.^[ref] Individual chemical signals can overlap or move in opposite directions while their sum remains unchanged. Total ion current normalization uses such a sum to rescale a spectrum, but the arithmetic does not independently establish chemical identity, detector linearity or equal response per molecule.