I once had continuing problems with gasoline from a station i used routinely, it kept clooginh the idle jet in the carburator. After 2 years,my car dealer found it was the gas, he took a sample and put it in a sealed glass jar and let it set for several days. The gas settled into 3 layers, water, diesel and gasoline. Easy to spot in the jar. Seems the gas station had a delivery of deisel dumped into a gas tank by mistake, they pumped it out but did not get much of it, so each load of gas mixed with the diesel. Also mixed with water in the tank. I suggest you put some in a sealed glass jar and see what settles out. If you want a scientific test, look for a general laboratory in your area and contact them to see they will do the content testing. I’m assumimg you are looking for contaimnents and don’t want octaine testing or propriatary additives. Old Motorist