Master Agreements (MA) are utilized when the County desires a list of pre-qualified vendors to perform various services, on an as-needed basis. As described in the DRMHP Policies and Procedures, the DRMHP.Rider to Development Agreement will include all federal and state requirements,. A master purchase agreement is a legally binding contract between buyer and seller, and typically relates to buying and selling goods rather than services. Fill out the information below, and attach documentation demonstrating the exemption approval. STEP 4: Negotiate Clinical Trial Agreement (CTA).