A novel apparatus was designed, built and tested to study the magnitude and direction of charge transfer in particle-particle collisions of insulator particles. This design ensured that the measured change in the charge of each particle was solely due to the binary collision between the particles. The collisions were confirmed by monitoring the particle trajectories using a high frame-rate camera coupled with particle-tracking software. This apparatus can aid in understanding the charge transfer mechanisms behind particle-particle charge transfer, leading to the development of an electrostatic model to simulate particle-particle contact charging in gas-solid flows. Upon preliminary testing of this apparatus with 3.18 mm diameter polytetrafluoroethylene (PTFE) particles, it was confirmed that triboelectrification solely due to the particle-particle collision can be observed. It was found that, if the particles carry low charges relative to their charge saturation point, their initial charge before collision does not dictate the direction of charge transfer. (C) 2019 Elsevier B.V. All rights reserved.