https://dx.doi.org/10.1351/goldbook.D01514
Non-SI unit of mass (symbol Da), equal to the unified atomic mass unit (atomic mass constant). It is often used in biochemistry and molecular biology although it was never approved by the Conférence Général des Poids et Mesures.
Source:
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 968