Evaluation of the extraction solvent
Acetonitrile was selected as sampling solvent because it adsorbs/dissolves the highest quantity of nicotine, comparing with the other two solvents used (i.e. methanol and dichloromethane). Moreover, an additional dilution and/or evaporation step could be needed if using dichloromethane.
Method validation
Aliquot samples containing 0.005, 0.02, 0.078, 0.313, 1.250, and 5 μg · mL-1 nicotine in acetonitrile were used for the method validation.
The calibration graph resulted from the analysis of the calibration standard solutions prepared in acetonitrile was linear during the entire range of calibration solutions with a regression curve: y = 2.83 · 107× - 5.51 · 105 and a determination coefficient of 0.9998. The limit of detection (LOD) was 100 ng · mL-1 and the limit of quantification was 300 ng · mL-1 (for details of calculation see Additional file 1).