tales of an ordinary girl

I really have a tough time with plants. I have a couple that have survived my care for five or six years, but most of my plants die within the first 5-6 months of having them.

Recently I transplanted a plant that I'd been given by a co-worker a few years ago. It really, really needed it. The plant had split off a couple of times, but I waited too long and the roots of the individual plants were massed together into a mess. So I teased on out and put it back in the original pot. I put the three others in a much larger pot and brought it back to work.

A couple of days after I brought it into work I noticed little gnat-like bugs in the plant. I don't mind bugs in my plants when they're outside, but this is in my office cubicle. Soon there were 10-15 little gnat things and it was, well, disgusting. Now the soil I used for transplanting was Miracle Grow, purchased at a garden store locally. And the plant only sat outside overnight. So either the bugs were in the soil or they migrated to it during that brief time.

I've sprayed the plant several times with a pesticide, actually to the point where I'm worried about breathing in too many fumes. The plant looks healthier than it has in years, but I'm still worried that I'll kill it off. And even after a few weeks the little bugs keep coming back. Is there a good way to get rid of them or should I take the plant home and re-pot from scratch (although I'm not sure I can get the bugs completely out of the roots)?