How To Fix A Broken Vinaigrette?
By definition vinaigrette is oil and acid of some kind plus salt/pepper, this dressing will not emulsify it will always separate so all you need to do is shake it well before using. If you wanted it to emulsify add some mustard to your acid(vinegar/lemon juice) whisk this well and then add oil slowly to it at first and than in steady stream. Hope this helps .
PS always dissolve salt in acid first before adding oil as you can't season your vinaigrette later because salt doesn't dissolve in oil