A common problem with office plants is an infestation of Fungus gnats. Fungus gnats are small, dark-colored flies that jump and fly across the office plant potting soil surface. Studies show that gnats are attracted to vinegar. Fill a jar almost to the top with vinegar, poke several small holes in the lid and then set it out.
The gnats will swarm to the jar, wiggle down into the hole, and will not be able to climb back out. If you set several of these traps around your office and monitor them to determine the highest concentration and subsequently find the gnat source.