Sorry to split hairs on this, but given that the typical half-life of nicotine is 2 hours, and that most assays have a limit of detection of 0.1 to 0.5 ng/ml, following the logic I described above, all the nicotine has gone from the blood stream within 24 hours. i.e. when you take a blood sample from a smoker 24 hours after their last smoke, they will most likely have a blood nicotine level <0.5 ng/ml. (i.e.>95% gone by 24 hrs).