2.3.1. GC-FID

The analyses were carried out with Varian 3800 GC system equipped with an FID detector. The columns used were: 30 m × 0.25 mm, 0.25 μm for cocaine, heroin and benzodiazepines. 25 m × 0.25 mm, 0.25 μm was used for methamphetamine. The temperature programs were: i) for cocaine and heroin and benzodiazepine, starting temperature was 210 °C (hold time: 1 min), raised to 280 °C (increase rate: 25 °C/min; hold time: 1 min) and then 300 °C (increase rate: 25 °C/min; hold time: 1 min); ii) for methamphetamine, starting temperature was 100 °C (hold time: 1 min), raised to 125 °C (increase rate: 25 °C/min) and then 180 °C (increase rate: 15 °C/min). The carrier gas used was hydrogen set at the constant flow of 1 mL/min. The injection volume was 2 μl.