Appendix - Mathematical Formulas

Retention Index

Also known as the Kováts retention index. For detected compounds, the Retention Index (RI) is calculated according to the following formula:

where t_r,j is the reduced retention time of compound j, calculated as the difference between the retention time of the compound (t_j) and the column dead time (t₀ = Unretained Peak Time). The subscipt i denotes the unknown compound, n denotes the calibrated n-alkene eluting before the unknown compound (n is the number of carbon atoms in this compound), and n+1 is the n-alkene eluting after the unknown compound.

Note that when creating a DHA Calibration from a DHA standard using the Create DHA Calibration... button in the Chromatogram window, it is necessary to fill in there the Unretained Peak Time (which is usually the retention time of methane), so that it is then saved in the DHA Calibration.

Corrected Area

The Corrected Area is calculated from the chromatogram peak Area multiplied by the relative response factor (RRF) as defined by the selected norm. RRF of a compound not present in the norm is considered as 1:

% Area

% Area corresponds to the percentage of the calculated Corrected Area of a compound divided by the sum of Corrected Areas of all N detected compounds:

% Weight

% Weight corresponds to the weight percentage of a compound in the sample. The calculation takes into account the Undetected Compounds amount:

% Volume

% Volume corresponds to the volume percentage of a compound in the sample. It is calculated by dividing the calculated % Weight by the relative density (RD) as defined by the selected norm, and subsequently normalizing this ratio to the sum of 100%: