Analysis of Volatile Toxic Substances Using Headspace GC/MS Part.2 - Cyanide and Azide

Importance of the Topic

Volatile toxic substances such as cyanide and azide present significant hazards in forensic investigations and industrial settings. Rapid and reliable quantification of these analytes in blood is critical for determining causes of poisoning, contamination incidents, and differentiating between accidental and intentional exposure. Conventional GC/MS methods involve derivatization and solvent extraction steps that increase workload and turnaround time.

Objectives and Study Overview

This study aimed to evaluate a streamlined headspace GC/MS approach for simultaneous measurement of cyanide and azide in hemolyzed blood using the same analytical conditions applied to ethanol testing. The main objectives were:

• Eliminate labor-intensive derivatization and extraction procedures.
• Establish calibration curves and assess method linearity for cyanide and azide.
• Evaluate intra- and inter-day precision and accuracy in a blood matrix.

Methodology

• Sample Preparation: Hemolyzed equine blood fortified with cyanide (0.15–10 µg/mL) or azide (1.5–10 µg/mL). Internal standard added: 1-propanol (0.5 mg/mL). Acidification achieved by adding ascorbic acid (0.1 M) and phosphoric acid (50 %) directly to vials.
• Headspace Conditions: HS-20 sampler; vial temperature 60 °C; equilibration time 10 min; loop mode; helium as pressurization and carrier gas.
• GC/MS Conditions: Rtx-BAC2 capillary column (30 m × 0.32 mm I.D., 1.2 µm film); oven program 40 °C (5 min) ramp to 200 °C at 40 °C/min; split injection (10:1 for cyanide/azide); mass scan range m/z 10–300; scan mode acquisition.
• Quantification Ions: m/z 27 for HCN (cyanide) and m/z 43 for HN3 (azide).

Used Instrumentation

• Shimadzu HS-20 Headspace Sampler
• Shimadzu GCMS-TQ8040 GC-MS/MS (alternative: GCMS-QP2020 single quadrupole GC/MS)
• Rtx-BAC2 Capillary Column (Restek Corporation)

Main Results and Discussion

• Cyanide: Demonstrated excellent linearity from 0.15 to 10 µg/mL (R ≥ 0.9999). Intra-day accuracy ranged 97.2–103.6 % with %RSD ~2 %. Inter-day reproducibility remained under 5 % RSD.
• Azide: Achieved linear response between 1.5 and 10 µg/mL (R ≥ 0.999). Intra-day accuracy spanned 94.3–114.5 % with %RSD ~7 %. Inter-day variations were within 2 % RSD. Although azide peaks exhibited broader leading edges, sensitivity met forensic requirements.
• Using identical headspace and GC/MS conditions for ethanol, cyanide, and azide facilitated rapid method switching and efficient batch processing.

Benefits and Practical Applications

• Bypassing derivatization and liquid extraction simplifies sample preparation and reduces analysis time.
• Method integration with routine blood alcohol testing enhances laboratory throughput.
• High precision and accuracy support reliable forensic toxicology and quality control workflows.

Future Trends and Potential Applications

• Extension of headspace GC/MS without derivatization to other volatile poisons such as sulfides and nitriles.
• Automation and online sampling integration for clinical, environmental, and industrial monitoring.
• Deployment of portable GC/MS systems for rapid, on-site toxicology screening at emergency scenes.
• Coupling with tandem MS/MS transitions to improve selectivity and detection limits in complex matrices.

Conclusion

This investigation confirms that direct headspace GC/MS under ethanol analysis conditions can accurately quantify cyanide and azide in blood. The streamlined workflow eliminates derivatization, maintains robust precision and linearity, and leverages existing laboratory protocols, thereby accelerating toxicological analysis and enhancing forensic response capabilities.