We report high-resolution (0."3-2") interferometric IRAM Plateau de Bure Interferometer observations of HCN, HCO+, and HNC emission in the high-velocity molecular outflow of the nearby quasar Mrk 231. We find that the three species have distinct, and differing, velocity structure consistent with chemical differentiation in the outflow. The most significant clump of each species appears in the same order in the red and the blue outflow (HCO+ at 600 and -450 km/s); (HCN at 500 and -400 km/s); (HNC at 350 km/s and -340 km/s). As the outflow appears to slow down with increasing radius, it suggests that the HCO+ gas is enhanced close to the nucleus and HNC farthest out in the outflow. A possible interpretation is that HCN emission is tracing the recently ejected gas which is interacting with the surrounding gas in a shock, HNC is primarily found in the slower post-shock gas, while HCO+ is found in faster gas closer to the nucleus before the shock. It is interesting to note that (again under the assumption of a decelerating outflow) the HCO+ enhancement is closest to the AGN - in contrast to more common interpretations of the HCN/HCO+ line ratio. In other outflows HCN-enhancements have been found (e.g. M51, NGC1068) and the enhancement is attributed to the interaction with a radio jet. If jet interaction occurs in Mrk 231 and is causing the HCN peak - it appears to happen a distance away from the nucleus.