Yeah, do not dip for the oil from the container. Even if you clean it really well, contaiminants will still get in there and cause your results to be skewed. Not hard to pull from the drain plug, just let the oil stream come out for a couple of seconds, slow a bit - then take your sample. You want to avoid grabbing the very first bit of oil draining out and the very last bit.
If you want to find out if the oil is protecting the oil correctly, you want to do a TBN or TAN test - both are checking the same thing, just reporting the number in a different way. Most shops recommend TBN, as that is a common way to compare lots of VOA (virgin oils analysis) - where people are interesting in the additive package in fresh oil. To do any extended motor oil study, TBN is a valid and popular measurement. TAN would be specfic to your particular car.
TAN is another test for finding out the percentage of acidic components in the oil. It is closely tied to TBN. Basically when TBN is high (brand new oil) - TAN will eb very low. As the oil is used, TBN will decline while TAN starts to rise. Depending on the conditions, TAN usually stays pretty low until TBN depletes to a 50-65% potection level, then TAN starts to increase. Eventually, TAN levels will be exceedingly high, usually coinciding when TBN drops to 30% or so.
More info here: http://www.machinerylubrication.com/read/2170/oil-drain-interval-tan-tbn