3.2. Instruments and Chromatographic Conditions

GC was performed on a Nexis GC-2030 system (Shimadzu Corp., Kyoto, Japan) with an HS-20 headspace autosampler. An analytical separation was performed using an SH-Rtx-Wax (polyethylene glycol) GC column (30 × 0.32 mm² i.d., 1 μm, Shimadzu America, MD, USA) placed in a column oven built-in GC system. Helium was used as a carrier gas. The temperature programing was set in a gradient mode using an initial constant temperature at 40 °C for 2 min, a ramping temperature of 20 °C/min to 240°C, and a holding temperature at 240 °C for 3.5 min. The carrier gas flow rate was set at 2.0 mL/min. The oven sample was heated up to 150 °C under a vibration level of 5 with an appropriate sample equilibrating time of 15 min. After equilibration, the sample vapor was pressurized for 1 min before 1 μL of the sample was injected under a gas pressure of 103 kPa with a split ratio of 3:1. The temperatures of the sample and transfer lines were set at 230 and 250 °C, respectively. The solvent cut time was set at 1 min. The filament was turned off at 9.0 min. The chromatographic run time was 15.5 min, and the cool down period was 1.7 min. Thus, the total analysis time was 17.2 min. The entire flow was directed into the detector.

Quantitation was achieved via MS detection in the EI mode for nitrosamine detection using a QP2020 NX mass spectrometer (Shimadzu Corp., Kyoto, Japan). The detector voltage was set at +0.6 kV. Both the ion source and the interface temperatures were set at 230 °C. NDMA (m/z 74.0), NDEA (m/z 102.0), DIPNA (m/z 130.0), and EIPNA (m/z 116.0) were quantified on a single-quadrupole mass spectrometer in the EI mode under the SIM acquisition method. The dwell time or event time was set at 300 ms. Quantitation of NDMA, NDEA, DIPNA, and EIPNA was based on their peak areas. Data were processed using Lab Solutions Software (GCMS Solution Version 4.50, Shimadzu Corp., Kyoto, Japan).