After supper (μετα το δειπνησα). Μετα and the articular aorist active infinitive, "after the dining" (or the supping) as in Luke 22:20.

The new covenant (η καινη διαθηκη). For διαθηκη see on Matthew 26:28. For καινος see on Luke 5:38; Luke 22:20. The position of εστιν before εν τω αιματ (in my blood) makes it a secondary or additional predicate and not to be taken just with διαθηκη (covenant or will).

As oft as ye drink it (οσακις αν πινητε). Usual construction for general temporal clause of repetition (αν and the present subjunctive with οσακις). So in verse 1 Corinthians 11:26.