Appropriations made for contingent expenses of the Senate shall not be used for the payment of personal services except upon the express and specific authorization of the Senate in whose behalf such services are rendered. Nor shall such appropriations be used for any expenses not intimately and directly connected with the routine legislative business of the Senate, and the Government Accountability Office shall apply the provisions of this section in the settlement of the accounts of expenditures from said appropriations incurred for services or materials.