to test or extract? to test, easiest way i've found to tell if an EO is diluted with DPG is to take a small bit of water, drop in a drop or two of your EO, swirl. DPG is water soluable, the oil is not. Take a dropper and extract some of the water below the floating oil.
dry that water on a slide, plate, or other hard surface (fan, light heat, sunshine, whatever). once the water is dry, if its oily, there was DPG or other water miscible content as a dilutant. pure sandalwood oil cleanly separates, so the water when dried would just be.. nothing, possibly trace calicium or dust if your water was extra hard, but not greasy.
to extract, (prob better ways here too), but what i did was dump my little container in water, swirl, thne put it in a separating funnel to remove the water leaving the oil behind, then use something like dried magnesium sulfate (heated epsom salt) to absorb the water, then filter to remove it, so now theres no tiny bits of water in your oil. better than nothing, but its not super awesome and likely some character lost in the extraction i assume.