Use of nitrogen as an alternative to helium in gas chromatography/mass spectrometry for forensic toxicological analysis.

Purpose: Although helium is commonly used as a carrier gas for gas chromatography/mass spectrometry (GC-MS), this practice is unsustainable owing to the unstable supply and rising prices of helium. Therefore, this study investigated nitrogen as an alternative carrier gas in forensic toxicology applications to suggest a simple transfer of analytical conditions.

Methods: GC-MS using nitrogen was compared with the conventional helium-based method for 34 compounds, including illegal drugs, medications, and pesticides. The targets were analyzed in a 10 µg/mL solution under constant linear velocity and pulsed splitless modes. Three analytical conditions were evaluated by varying the linear velocity and ionization voltage.

Results: With nitrogen as the carrier gas, the average peak height was 10% compared to that with helium. The similarity index of the obtained mass spectra and that acquired with helium averaged at 84. However, under conditions at which the velocity decreased, the peak height was approximately the same, whereas the spectral similarity index increased to an average of 91. Furthermore, under conditions in which the ionization voltage was changed, the spectral similarity index slightly decreased to an average of 81, whereas the peak height significantly increased to an average of 87%.

Conclusions: Although analysis using nitrogen with the same level of detection sensitivity as that used with helium was challenging, qualitative analysis was considered sufficient for samples with high concentrations, such as powders, tablets, liquids, and plants. Thus, nitrogen can serve as a viable alternative carrier gas to helium in GC-MS analysis.