 Chromatographic baseline-area uncertainty

Chromatographic baseline-area uncertainty quantifies uncertainty in the integrated baseline subtracted when assigning a chromatographic extracted-ion chromatogram peak area. For an extracted-ion chromatogram baseline $b(t)$ over fixed limits $t_1,t_2$, let $B={\int }_{t_1}^{t_2}b(t)dt$. The baseline's uncertainty is shared across time whenever fitted parameters or other common inputs are shared.

For sampled times with integration weights $w_i$ and baseline estimates $b_i$,The weights include the actual sampling intervals and chosen integration rule. This is correlated-input uncertainty propagation, not an assumption that each drawn baseline point is independently uncertain.^[ref]

An original constant-baseline example uses 100 equal intervals of $0.1\min$ and one common fitted baseline with standard uncertainty0.2 signal units. Its integrated uncertainty is $10(0.2)=2$ signal-unit minutes. Treating those 100 appearances of the same fitted quantity as independent would instead give $\sqrt{100}(0.1)(0.2)=0.2$, underestimating uncertainty tenfold. More sampling points do not average away a shared offset.

For total recorded area $P$ and assigned peak area $Q=P-B$,With stipulated $u_P=0.5$, $u_B=0.4$ and correlation coefficient0.6, the result is $u_Q=\sqrt{0.17}\approx 0.412$ area units, compared with 0.640 under independence. The appropriate covariance depends on how the trace and its baseline were estimated; it cannot be selected to obtain a preferred uncertainty.

Changing integration limits or choosing a different baseline form can create additional effects beyond parameter uncertainty within one fixed model. Inspect neighboring peaks and baseline regions, and record the fitted model and boundary choices. A precisely computed extracted-ion chromatogram peak area can still depend on an unsuitable baseline model.