I've started my first runthrough as an Adept, and blowing groups of baddies up with a singularity-warp combo is really fun, but sometimes it works and sometimes it doesn't, so what's the secret.
Any lasting biotic power can be detonated by any "direct" biotic power. Warp, Reave and Dark Channel fulfill both roles but can't detonate themselves. In case of Stasis, Pull and Singularity, the enemy is freed from the power after sustaining some damage. Most likely, you've been unable to detonate enemies when they sustained enough damage to break free from Singularity and started falling to the ground. Mitranim
Also detonation will only occur if the effect of a power still affects them. For example, when using Pull on an unshielded/unarmored opponent, their body will glow blue as they float through the air. This indicates that a combo is possible; applying warp, shockwave, throw, or other catalyst powers (including Slam in ME3) will cause a biotic detonation. Keep in mind the highest damage biotic combo will almost always be [singularity, pull, lift grenade, shockwave (lifting shockwave in ME3), Reave, Dark Channel] + Warp, especially if the evolution to increase biotic detonations is taken. This is because warp has the highest base damage; the target will recieve a massive damage dose from the Warp itself as well ass the detonation; whereas using any other detonator will have varying effects but almost always less damage. For rapid fire high damage with an Adept, I recommend spamming Pull + Warp. In ME2, you can upgrade Pull to be a Pull Field and lift multiple targets, and in ME3 you can upgrade it have a Field AND fire 2 projectiles instead of just one. Pull also has one of the quickest cooldowns, allowing plenty of chaining. Lifting Shockwave is another viable option, although it is limited on range. Shockwave can actually be used to detonate several biotic abilites at once, if positioned properly. If the Shockwave blast radius includes 2 seperate enemies who have a reactable field (like pull) on them, and they're far enough away from eachother that the biotic detonation won't affect the other, the shockwave will actually cause 2 detonations as it catalyzes both pull effects.