Air Carrier Captain reported a fumes event during approach. The odor was described as a 'burning oil and acrid'. Flight crew donned oxygen masks and executed a safe landing. Upon gate arrival an aircraft logbook entry was submitted to maintenance.

Narrative

While descending through 5;000 ft. over Lake X; we encountered a strong fume / odor event in the cockpit. The smell could be described as burning oil; acrid and very chemically in nature. After what must have been just a couple seconds; the First Officer (FO) asked; 'do you smell that?' After which; we both donned our O2 masks and continued the approach and landing. Note; the O2 masks remained on until reaching the gate where upon engine shut down the cockpit windows were opened for ventilation. Upon removing our oxygen masks; we did not smell any of the odors as described above in the cockpit. After this; we asked the F1 if they smelled anything out of the ordinary on the approach--they did not. Upon recording the event in the aircraft logbook; I was selected for a drug test; and the FO departed for the crew room. In regards to the aircraft configuration at the time of the fume / odor event: the aircraft was in a managed descent descending through 5;000 ft. with thrust at idle; and flaps in configuration 1. The APU was placed on MEL (for fume / odor event) and both PACKS were ON. The Cockpit Odor Report was completed later that evening.