Simple and simultaneous quantification of cyanide, ethanol, and 1-propanol in blood by headspace GC–MS/NPD with a Deans switch

Abstract

This study aimed to develop a method to simultaneously quantify cyanide, ethanol, and 1-propanol in blood using headspace gas chromatography–mass spectrometry/nitrogen-phosphorus detection (HS–GC–MS/NPD) with a Deans switch. Cyanide is a powerful and rapidly acting poison. However, routine cyanide testing can be costly and time-consuming, given that cyanide poisoning rarely occurs in Japan. Therefore, we attempted to combine cyanide and routine alcohol (ethanol and 1-propanol) testing using HS–GC–MS/NPD with a Deans switch. 1-Propanol can be used as an indicator of putrefaction. NPD is advantageous over MS in terms of sensitivity for cyanide detection, and the Deans switch allows for switching between two detectors in a single run. Three analytical columns with different characteristics were investigated to achieve adequate separation. In addition, we verified whether 18 other volatile compounds could be simultaneously detected using this system. The following instruments were used: 7697A headspace sampler, 7890A GC, 5975 C MS, and NPD via a Deans switch (Agilent Technologies); Columns: PoraBOND Q (25 m × 0.25 mm × 3 μm), CP-Sil 5 CB (25 m × 0.25 mm × 1.2 μm), and HP-INNOWax (30 m × 0.25 mm × 0.5 μm). For sample preparation, whole blood (0.1 mL) was placed into a 10-mL headspace vial, and 50 μL of internal standard (IS) mixture (4 μg/mL propionitrile for cyanide, and 1 mg/mL ethanol-d6 for ethanol and 1-propanol) and 20 μL of 0.5-M ascorbic acid were added. After capping, 21.25% phosphoric acid (0.1 mL) was added to the vial using a syringe. The vial was incubated at 60 °C for 20 min, and 1 mL of the headspace was automatically injected into the GC–MS/NPD system. The target compounds were cyanide, ethanol, 1-propanol, sulfide, azide, 1,1-difluoroethane, methanol, acetaldehyde, acetone, butane, isobutane, pentane, hexane, heptane, octane, nonane, chloroform, benzene, toluene, ρ-xylene, and styrene. Among the three columns investigated, PoraBOND Q achieved the most effective separation, and its sensitivity was equal to or greater than that of the other columns for all compounds, except hydrogen azide; therefore, PoraBOND Q was selected. After selecting the analytical column, the switching times of the Deans switch were determined. All 23 compounds, including the IS, were successfully detected. The calibration curves for cyanide, ethanol, and 1-propanol were linear, and their R2 values were >0.999. The intra- and inter-day accuracy and precision were <15%. Forensic laboratories must conduct several blood examinations, including biochemical test, alcohol test, and drug screening. However, obtaining a sufficient amount of blood during an autopsy can be occasionally challenging. This method allows simultaneous quantification of cyanide, ethanol, and 1-propanol in a single run with a small amount of blood (0.1 mL). In this method, a chief feature is that only the part where hydrogen cyanide or propionitrile (IS) appeared was cut into NPD, improving sensitivity to cyanide. Although the Deans switch chooses one of two detectors, sufficient separation achieved using the PoraBOND Q column enabled the detection of all target compounds in this system. A simple and simultaneous quantification method for cyanide, ethanol, and 1-propanol in blood was developed using headspace GC–MS/NPD with a Deans Switch. This method could also detect 18 other volatile compounds. Therefore, this method could be valuable for the routine analysis of volatile compounds in forensic practice.