- No concentration is calculated for some unknowns. The peak codes shown are Q54 and Q56, which indicate a problem with the x value of the internal standard. However, the x values for the internal standards are set correctly to 1 and work for all the other samples.
- UNIFI 1.8 (workstation and network)
A change related to the use of internal standards was introduced in 1.8 and is detailed in US1#181031. When using an internal standard, the IS level must be specified for all injections or for none of the injections.
FIX or WORKAROUND
- Remove all concentration values for the internal standard from the Default amounts table in the analysis method; update and reprocess.
The software then makes the assumption that the internal standard level is 1 for all injections and gives a calculated concentration as expected. In this case, there will be no information regarding the deviation of the IS from the expected concentration.
Add a new level specifically for the IS. Add a new level to the Default amounts table and populate only the IS component:
Then add this level to all samples that you want to quantify with IS (in this case, using the sample editor):
Update and reprocess. This will give calculated concentration values and show the deviation of the IS from the expected values: