Prime doesn't necessarily remove copper from your tap, it's kind of a bonus when it does. This is taken from the thread "Copper @ 1.0?" thread on the front page:
Prime won't remove anything so your test won't tell you anything about whether or not the prime is detoxifying the copper. According to Seachem it won't really do anyhting to detox that much copper. Here is a quote from a seachem rep on another forum:
"Hello thanks for the question. The important thing to remember is that the primary functions of Prime are to detoxify chlorine, chloramine, ammonia, nitrite, and nitrate. While it will also help to detoxify heavy metals, this is more of a side effect and may not be the most effective means for you. Because Prime will preferentially bind with the other mentioned compounds, it is hard to say how much of any available heavy metals will be detoxified. An RO unit is a much more effective means of removing any heavy metals instead of relying on Prime to remove some of them. With Prime, it is really just an added benefit that any Prime that is active after detoxifying chlorine, chloramine, ammonia, nitrite, and nitrate will then detoxify as many heavy metal ions as well."