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Capillary electrophoresis separates species by their motion in an electric field inside a narrow liquid-filled tube. In its free-solution form, different electrophoretic mobilities produce different drift speeds; a detector at a fixed position records the arriving bands as an electropherogram. The liquid itself can also move by electroosmotic flow, so arrival order is not determined by molecular charge alone.

A simple apparatus places the ends of a capillary in two buffer reservoirs containing electrodes. An applied electric potential difference drives migration along the tube; a detection window interrogates the passing material. In the uniform-field model, with total capillary length $L$, detector distance $L_d$ and signed applied potential $U$,The last expression requires net motion towards the detector. Thus a neutral marker can move with electroosmotic flow even though its electrophoretic mobility is zero. The instrument's distinction between total length and detector distance matters when converting migration times into apparent mobility.^[ref]

For an original ideal example, take $L=0.50\mathrm{m}$, $L_d=0.40\mathrm{m}$ and $U=20\mathrm{kV}$. Two net mobilities $(4,5)\times 10^{-8}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ give speeds $1.6$ and $2.0\mathrm{mm}{\mathrm{s}}^{-1}$ and migration times 250 and 200 s. These are model values, not assigned chemical identities. Band widths from diffusion, injection and other dispersion mechanisms determine whether the time difference is actually resolved.

Narrow tubes also help remove Joule heating. For a uniform cylindrical liquid conductor, heat generation per volume is $\sigma E^2$, with electrical conductivity $\sigma$, while wall area per liquid volume is $2/a$ for tube radius $a$. This geometric scaling motivates small bores, although temperature control still depends on heat transfer through the wall and surroundings. Increasing the electric field indefinitely is therefore not a free route to perfect separation.

A primary 1981 demonstration used a 1 m glass capillary with 75 micrometre internal diameter, a 30 kV applied potential and a fluorescence detector. It resolved fluorescent derivatives of amino acids, peptides and urinary amines. The observed result was separated fluorescent zones; the need to derivatize the samples was an explicit detection limitation.^[ref]

An electropherogram is a recorded trace of an electrophoresis separation. In capillary electrophoresis, it commonly plots detector signal against migration time: separated populations reach a detection window at different times and produce peaks. Peak position, width, height and integrated area describe different features of that trace.

The position depends on the migration mechanism and geometry. In a simple uniform-field model with detector distance $L_d$, electric field $E$, electrophoretic mobility ${\mu }_{\mathrm{ep}}$ and electroosmotic flow represented by mobility ${\mu }_{\mathrm{eo}}$,when the resulting drift is towards the detector. A changed buffer-flow contribution can therefore shift migration times without changing the analyte's identity. The instrument's actual timing and mobility conventions must be specified; the first-party software documentation gives its explicit migration-time and apparent-mobility definitions.^[ref]

An electropherogram peak area is the integral above an assigned baseline. For an original Gaussian-component model,The component area is $A_i$, while its height above baseline is $A_i/({\sigma }_i\sqrt{2\pi })$. Choose $(A_1,{\sigma }_1,t_1)=(1,0.4,5)$ and $(A_2,{\sigma }_2,t_2)=(2,0.8,10)$ in compatible signal/minute units. The two component heights are equal, although the second has twice the integrated signal. These are synthetic components, not experimental analyte concentrations.

The cited software defines time-corrected area as $A_i/t_i$.^[ref] In this example, both corrected areas are $1/5=2/10=0.20$. This is another observable, not permission to equate every corrected area with an absolute amount without response calibration and an appropriate measurement model.

A peak can also contain unresolved co-migrating species. Its apparent simplicity does not establish chemical purity. Useful interpretation therefore combines the trace with baseline selection, migration references, detector response and independent identification evidence, rather than treating each visible peak as a complete chemical explanation.

An electropherogram peak area is the time integral of detector signal above an assigned baseline over a specified peak interval:Its units are signal multiplied by time. It differs from peak height and from the amount of material unless a detector-response and transport model connects them. Broadening a peak can lower its height while preserving its area.

For an isolated Gaussian distribution of signal, $s-b=H\exp [-(t-t_m{)}^2/(2{\sigma }_t^2)]$, integration over the complete peak gives $A_p=H{\sigma }_t\sqrt{2\pi }$. An original peak with $H=2$ signal units and ${\sigma }_t=3$ s has area $15.04$ signal-seconds. Doubling the width at unchanged area halves the height. Integrating only a finite interval loses the corresponding tails; integrating overlapping peaks can include another species' response.

Why can migration time enter quantification? Suppose a concentration-sensitive detector gives $s-b=kc$ for a band moving at constant speed $v$ through a capillary of internal area $S$. The amount passing the detector isSince $v=L_d/t_m$, $n\propto A_p/t_m$ at fixed $S$, $L_d$ and response coefficient $k$. A slow band spends longer in the detection window and can have more raw time-integrated signal for the same amount. This motivates time-corrected electropherogram peak area; the first-party software explicitly calculates it as raw area divided by migration time.^[ref]

For stipulated raw areas 120 and 180 signal-seconds at migration times 200 and 300 s, both corrected values are 0.60 signal units. Equal corrected values imply equal modeled amounts only if the relevant response coefficients and sampling conditions agree. Different species need not have equal detector responses, and a detector measuring a different physical observable requires its own model.

Baseline error has an especially simple consequence. If the estimated baseline exceeds the true one by $\delta b$ throughout a window of duration $T$, the area error is $-\delta bT$. A 0.01 signal-unit offset over 60 s subtracts 0.60 signal-seconds. Blank measurements, explicit integration limits and inspection of unresolved neighbors therefore matter even when the numerical integration itself is exact.

A time-corrected electropherogram peak area is a raw electropherogram peak area divided by its migration time,It compensates for the longer passage time of a slower band through a concentration-sensitive detector in capillary electrophoresis. The first-party processing documentation defines this quantity explicitly and computes a percentage by dividing each corrected area by the sum of corrected areas.^[ref]

The transport model explains the correction. If the baseline-subtracted detector signal is $kc(t)$, internal capillary area is $S$ and band speed through the window is constant $v$, thenWith detector distance $L_d$ and $v=L_d/t_m$,Thus dividing the time integral by migration time removes one speed dependence. It does not determine the response coefficient $k$, injected sample amount or chemical identity.

For an original example, two peaks have raw areas 90 and 150 signal-seconds and migration times 150 and 300 s. Their corrected areas are 0.60 and 0.50 signal units. With equal detector response coefficients, their modeled relative amounts are $6:5$, giving $54.55\%$ and $45.45\%$ of the corrected total. Raw-area normalization would instead give $37.5\%$ and $62.5\%$.

Species-dependent detector response remains important. If the first coefficient is twice the second, amounts are proportional to $0.60/2$ and $0.50/1$, giving $37.5\%$ and $62.5\%$ instead. Equal normalized corrected areas therefore need not mean equal amounts when the detector responds differently to the species. A measurement calibration must match the response and sample conditions being interpreted.

The reduction also assumes each band travels at a representative constant speed. If the electric field or electroosmotic flow changes substantially during a run, $L_d/t_m$ is an overall migration speed and need not equal the speed during detection. Baseline error, unresolved neighbors and nonlinear detector response are likewise not repaired merely by dividing by time. The software's chosen migration-time definition is part of the calculation: its CE mode uses the peak apex, while its CIA mode uses the midpoint of the start and end times.^[ref]