§1. A priest who celebrates several Masses on the same day can apply each to the intention for which the offering was given, but subject to the rule that, except on Christmas, he is to keep the offering for only one Mass and transfer the others to the purposes prescribed by the ordinary, while allowing for some recompense by reason of an extrinsic title.
§2. A priest who concelebrates a second Mass on the same day cannot accept an offering for it under any title.
Source: Code of Canon Law (Vatican.va)