Morgan Stanley Capital Partners, a middle-market private equity arm, has acquired Apex Companies, a provider of environmental consulting and engineering services, from Sentinel Capital Partners.

Apex, headquartered in Rockville, Md., focuses on a range of environmental and infrastructure needs. It serves a client base spanning both the public and private sectors and a range of end markets including energy, industrial, manufacturing, real estate, retail and telecommunications. Sentinel Capital Partners will maintain a minority position in Apex.

Robert W. Baird & Co., Houlihan Lokey, and AEC Advisors served as financial advisors to Apex.