Gas chromatography–mass spectrometry determination of nicotine and cotinine in urine: A study of the effect of passive smoking

Rationale

Recent data suggest that passive smoking has a risk comparable to active smoking. Passive smoking is considered dangerous in children and is suspected as a cause of asthma. However, some reports are opposing such claims, indicating the need for solid results and large-scale studies. This scientific work aims to develop a method for the determination of nicotine (NCOT) and major nicotine's metabolite cotinine (COT) in urine samples, using gas chromatography–mass spectrometry (GC–MS).

Methods

Analysis was performed using a gas chromatograph Agilent Technologies 7890A with an MS 5975C inert XL, EI/CI MSD with Triple-Axis detector. For sample preparation, liquid–liquid extraction was applied after an optimization study with different extraction media. Eventually, 1 mL of dichloromethane was selected for the extraction of 0.5 mL of urine. Suitable chromatographic conditions were found for the rapid and accurate determination of NCOT and COT. Injection of 2 μL was performed using GC–MS, and selected ion monitoring (SIM) analysis was performed with the following ions (m/z): 162 (quantifier ion) and 84, 133, 161 qualifier ions for NCOT, and 176 (quantifier ion) and 98, 118, 119, 147 qualifier ions for COT. Nicotine-D4 (NCOT-D4) and cotinine-D3 (COT-D3) were used as internal standards with quantifier ions 101 and 166, respectively. The retention time (Rt) for NCOT was 7.557 min and 9.743 min for COT.

Results

The method was validated following international principles, assessing characteristics such as absolute recovery, carryover, linearity, specificity, selectivity, accuracy, precision, and stability. The method showed a linear dynamic range from 0.5 to 50 ng/mL, and the limits of detection and quantification were for both NCOT and COT 0.2 and 0.5 ng/mL, respectively. Validation results were found satisfactory. Finally, the method was applied to the analysis of 60 clinical pediatric samples obtained from Aristotle University's pediatric clinic to check for possible exposure to smoke. Concentration levels ranged between 0.5 and 16.2 ng/mL for NCOT and between 1.0 and 25.1 ng/mL for COT.

Conclusions

A rapid, sensitive, accurate, and simple method was developed and used as a tool for the confirmation of passive smoking in children. It is the first method applied to the analysis of such samples belonging to nonsmokers of young age. The total runtime of the GC–MS analysis was short (20 min), and the pretreatment protocol was simple, giving the ability for analysis of a large number of samples on a daily routine basis.