Check church or census records on him to see if they give a German state for his place of birth. If so, you can tell which Frankfurt it is. You also might look online at the Immigrant Ships website to see if your ancestor's crossing is there and again a German state for place of birth. Also his death record might say.
You can expect to see a spelling change from Langfeld to Langfald, I am almost certain, along the way. "Langfeld" is common; the other I've never seen.