as的词性

as per sth（following sth that has been decided）中的as应该是介词吧。

还有as per usual，这里的as词性。

The work was carried out as per instruction.

It also require grain purchasers to conduct quality checks as per national rules.

as per 应该看作一个介词，不要拆开剖析。as per = in accordance with 依据。