Definition of a timed group

A timed group contains one or more time regions and is defined on a specific signal. The expected retention time of the group is for sorting purposes only and can be entered manually.

The timed group corresponds to the uncalibrated range or calibrated range in OpenLab EZChrom.

The following example shows three timed groups, where Group 2 and Group 3 overlap. C1 and C2 are identified compounds. The unidentified peak at 5.689 min is evaluated in both groups. Identified peaks are only evaluated if the group parameters are set accordingly.

Groups	Time ranges	Include identified peaks?
Group 1	0.8 min - 1.4 min 2.8 min - 3.4 min	No
Group 2	3.8 min - 5.9 min	Yes
Group 3	5.4 min - 7.2 min	No

 

Example: Timed groups

If a timed group has no time region defined, its area, height, and amount are not calculated. If a timed group has a region or regions defined, but no peak is found in this region or these regions, its area and height are equal to zero.

If you correct the retention times by using time reference compounds, the start time and stop time of the timed group are also corrected by the corresponding shifts (see Calculations for time reference compounds).

For quantitation, the area, height, or scaled response of the group is calculated by summing the corresponding values of the individual peaks contained in the time ranges (including or excluding identified peaks, depending on the group parameters).

A timed group is calibrated and quantified using the calibration parameters for the group. Timed groups support all calibration and quantitation modes of regular compounds (Curve, Manual Factor, Reference). In the group parameters, you can choose to quantify all peaks individually. In this case, each peak of the group is quantified individually with the group response factor (RF).

Caution: As Timed Groups use the calibration parameters of the whole group, caution should be taken when using with nonlinear and/or calibration curves with a large offset.

Usage of a Timed Group with nonlinear calibration curves is not recommended as it will calculate potentially imprecise results due to the noncommutative nature of the calculations.

If a group calibration curve has a significant off-set (that is, a large intercept (b) value), the offset gets equally distributed across all peaks found within the time group windows. The equal distribution may not describe each compound adequately.

Conflicts may occur if a peak belongs to several groups, or if identified peaks are quantified as part of the group. For details on the conflict resolution, see Evaluation of timed group parameters.