Grouped substances

TUCAVOC can group substances in a new one. For example you have substances A, B and D, and you want to make a new substance called S.

S is a grouped substance.

Grouped substances are usually used when you have coeluting substances, that come sometimes in one peak and sometimes in different peaks.

Calculation

TUCAVOC will handle this case by simply adding the amount fraction of the individual substances contained in the group. The uncertainty of the amount fraction calculated for the grouped substance is calculated applying the squared sum of the uncertainty of each substance.

Behaviour for flagging and missing data

If one or more group members have invalid data (nan values), the group will be flagged as invalid.

If the area of a substance is zero, TUCAVOC assumes that the substance was included in the area of another substance from the group.

Groups selection in TUCAVOC widget

You can select which group a substance belong to, using the combo box in the substances widget. You can also create a new group using the ‘+’ button at the top of the Group column.

If you want a substance to be present only in a group, but not in the output, you have to untick the include substance column, and add a group for the substance. TUCAVOC will automatically remove that substance from the output, but still include it in the calculation of the grouped amount fraction and in the calculation of the mean CRF (if selected in the use for general crf column).

Mean carbon response factor calculation

Substances in the same group will share the same mean_carbon_response_factor value. This means that only substance in the calibration for that group are taken into account in this calculation.

For substances not in any group, the mean_carbon_response_factor is taken to be the mean of all substances in the calibration that do not belong to any group. This is the general mean_carbon_response_factor.

As a suggestion for the general mean_carbon_response_factor, we recommend using all the substances having from 2 to 4 carbon atoms, excluding ethyne.