Below are the steps I took in preparing my sample of 10w40 motor oil:
First I measured 14ml of 10w40 into a an empty glass jar, then I poured the same amount of Isopropyl alcohol and shook pretty well and let it sit for a few hours. When you see the light colored layer add about .25mg of table salt and shack it again. Let it sit overnite (this is called "salting out.") The salt will extract the rest of the Isopropyl alcohol from the sample and you will se a very distinct clearer layer on top.
This is what the "salted" top layer will look like.
Remove very carefully the top "salted" layer using a glass pipette as shown above, I placed the layer in a test tube so you could see the layer's color.
This is what your sample should look like in the glass jar, remove the bottom layer from the jar and place it in either a test tube like this or something else that you want to use.
Below are pictures of my solvents and lab separation equipment I used:
Below is what the final sample under a UV405nm laser pointer, it will fluoresce a blueish-white color namely because it's specific gravity is over 40.