Chemical Thrower + Electric Gel = Boss justs stand there taking damage while you unload the stuff. Then just use either Grenade Launcher, Shotgun or Crossbow to finish it off.
that might have worked aswell, afterall i have plenty of ammo on my savegame, i used the power boosted healing wrench on random encounters which
gave me the oppertunity to buy max ammo on every weapon, when i finished the DLC trophies (which are only 2 at the moment) i might re-do the boss to see how that goes.
Going through the rest of my Bioshock 1 on Hard playthrough... I better get cracking with the photographs; I'm still missing the big daddy and little sister research to get my achievements for that.
good for you that the films are cheap, just max them out and take as much pictures of every subject as possible.
just in case there are more bioshock players that want to acchieve 100%, here's a trophyguide for the game: http://www.allps3trophies.com/forum/retail-games-guides/bioshock-trophy-guide
it works for both Xbox and PS3 users, have fun.