Urinary excretion of exposure biomarkers ( nicotine equivalents -LSB- NE -RSB- , total and free @ - ( methylnitrosamino ) -@ - ( @-pyridyl ) -@ - butanol -LSB- NNAL -RSB- , @-hydroxypyrene , and @-hydroxypropyl mercapturic acid ) as well as carboxyhemoglobin and plasma cotinine were measured at baseline , Day @ , and Day @ .