Excel 两个单元格重复数据删除的问题

Sub chiefzjh()
Dim mSr, mTr, a, t
mSr = Split([a1], ",")
mTr = [a2]
For Each a In mSr
If InStr(mTr, a) = 0 Then t = t & a & ","
Next
[a3] = Left(t, Len(t) - 1)
End Sub