What chemical test can be used to tell apart meat and plant-based meat?
There are a lot of things you could test for.  The thing that come to mind off the top of my head is cholesterol.  This will be present in all animal meat, since all animals muscles contain cholesterol, whereas meat substitutes usually do not.
That said, there are other options as well (such as starch vs. glycogen levels, for example), and even molecules such as collagen differ between plants and animals, so a careful analysis (provided the proteins have not been too altered by the commercial production process) should be able to reveal thousands of differences, even in molecules found in both plants and animals.
Further reading

Marzetta CA, Rudel LL. 1986. A species comparison of low density lipoprotein heterogeneity in nonhuman primates fed atherogenic diets. Journal of Lipid Research.  27: pp. 753-762