Because taking the bloodline elements out of the blood didn't work, Alex took the opposite approach. He took every other element out of the blood, leaving behind just the plain blood along with the one bloodline element that was required.
After referencing hundreds of different samples of blood, he knew for more than certain what plain blood was, so just keeping one bloodline element in it was a rather easy task.
Of course, the Azure Dragon's bloodline consisted of more than just a single bloodline element, but Alex was just testing things out now.
His attempts were successful on the first try after getting used to the task for so long, and Alex was left with a cup full of blood that held just the one bloodline element he had wanted.
