How to detect cuts: if you intend to use a synthetic substance, first you need to check it using a test kit. Most popular drug testing kits are colorimetric reagents, simple spot-tests which produce different color reactions with different compounds. It’s the same kind of tests as used by police. To detect fentanyl or it’s analogues it’s recommended to use fentanyl test strips.
How to test drugs? adulterants basics cuts guide