The phrase "purity level" refers to how clean or free of impurities something is. It shows how much of the substance is in its purest form, without any other substances mixed in. Full definition
So isolate comes at a higher purity level, but it does come at a higher cost as well. (nupush.net)
The best thing about this process is that gold and cadmium are mixed in the ratio of 92:8, which results in solder purity level of 92 percent. (policybazaar.com)
A comparison of heroin purity levels in batches seized by the UK Border Agency and the police in 2007/08 showed it was 54 % pure on import, 51 % at street. (politics.co.uk)