Depends on what of the options you use for limit calculation and also depends on the detections to see what is most optimal.
Note that initially you are always starting from the individual limits, only when both NDSRI exceed 10% of their individual limit you would have to go into group limit setting in my opinion.
You can of course proactively start from methods reaching LOQ at least 10 ng/day for both nitrosamines if practical.
Some examples:
