How to detect if a beverage has Sucralose or aspartame?
Here's the structure of sucralose



and here is the structure of aspartame



They are very different one from the other and should be easily separable.  You can do a "poor man's" separation using paper chromatography.  Aldrich sells both of these materials, but I'm sure you could find them much cheaper at a local Health or Health Food store.  Get the samples and some filter paper.  You'll need some solvents, a tank (preferably glass) with a lid, some filter paper coated with a fluorescent material (as an easier, but more expensive alternative, you could always buy some TLC plates from a chemical supply house) and a black light.  Put one of the solvents in the tank so that it is 1/8 - 1/4" deep.  Put the top on the tank and let it equilibrate. Make dilute solutions of your known samples using the same solvent that's in the tank.  Using the tip of a needle or a toothpick place a small spot of each of the dissolved materials on the filter paper, put the spots about 1" apart and high enough above the bottom edge of the filter paper so that they will be above the solvent level when you place the filter paper in the tank.  Give the spots a moment to dry and then put the spotted paper in the tank.  Watch as the solvent level climbs up the filter paper (or tlc plate) and remove the filter paper when the solvent is about 3/4 of the way up the paper or plate.  Let the paper or plate dry and then examine it with the black light.  The paper should fluoresce under black light except where the two spots have migrated up to.  The spots cover the fluorescent material and will appear as dark spots under the black light.  If you got a good separation between the two spots stop here and repeat the experiment putting a spot of your diluted drink on a new piece of filter paper along with spots of the two known materials.  Rerun it in the tank and see if there are any spots in your drink that match either of the spots from the two known compounds.  If there is no match, then sucralose or aspartame are not in your drink.  If there is a match, then whichever spots matched might be in your drink - more advance experiments will be needed to further analyze the situation.  If you didn't get a good separation between the spots for the two known compounds to begin with, start over and repeat with different solvents until you do get a separation.