Dim dt1 As New DataTable
dt1.Columns.Add("angelegt am", GetType(DateTime))
dt1.Columns("angelegt am").AllowDBNull = True

Dim mydate as DateTime
Dim newrow As DataRow = dt.NewRow
 
If DateTime.TryParse(arr(0), mydate) Then
   newrow("angelegt am") = mydate
Else
   newrow("angelegt am") = DBNull.Value
End If