A Gas Chromatography–Thermal Conductivity Detection Method for Helium Detection in Postmortem Blood and Tissue Specimens

Journal of Analytical Toxicology 2012;36:112 –115 doi:10.1093/jat/bks002 Article A Gas Chromatography– Thermal Conductivity Detection Method for Helium Detection in Postmortem Blood and Tissue Specimens† Jason E. Schaff1*, Roman P. Karas1 and Laureen Marinetti2 1 Federal Bureau of Investigation Laboratory, Quantico, Virginia, and 2Montgomery County Coroner’s Office, Dayton, Ohio * Author to whom correspondence should be addressed: Jason E. Schaff, FBI Laboratory Chemistry Unit, 2501 Investigation Parkway, Rm 4220, Quantico, Virginia, 22135. Email: . In cases of death by inert gas asphyxiation, it can be difficult to obtain toxicological evidence supporting assignment of a cause of death. Because of its low mass and high diffusivity, and its common use as a carrier gas, helium presents a particular challenge in this respect. We describe a rapid and simple gas chromatography –thermal conductivity detection method to qualitatively screen a variety of postmortem biological specimens for the presence of helium. Application of this method is demonstrated with three case examples, encompassing an array of different biological matrices. Experimental Introduction Standards and controls Standards of pure helium and pure air were prepared by filling 250-mL volumetric flasks with DI water, inverting in a DI water bath, and then bubbling in the appropriate gas to completely displace the water. The flasks were capped with rubber “turnover septum” stoppers, providing an airtight seal, before being removed from the water bath. Standards of helium in air were prepared by filling 100-mL volumetric flasks with air, as described, just to the volume mark and then injecting appropriate amounts of the pure helium standard through the stopper into each flask with a 3-cc plastic syringe. Standards were prepared at concentrations of 0.5%, 1%, 2%, 3%, and 4% (v/v), each in a separate flask. The 4% standard was prepared with two consecutive 2-mL injections. Negative control samples of DI water and of whole blood were prepared by measuring 10 mL of the appropriate matrix into 16-  100-mm culture tubes, capping with rubber septa, and then venting the headspace in each tube to vacuum for 5 s through a syringe needle. Positive control samples of DI water and of whole blood were prepared from 10-mL aliquots of matrix measured into 16-  100-mm culture tubes which were then capped with rubber septa. Each sample was two-needle sparged with a gentle flow of helium for 30 min to saturate the matrix. The vent needle was fitted with a 0.2-mm PTFE syringe filter to contain the resulting blood foam, with approximately 0.5 mL of the blood sample lost to foaming. After settling, the headspace of each sample was vented to vacuum for 10 s through a syringe needle to remove any undissolved helium. Though asphyxiation has been a well-known means of suicide for decades, deliberate use of inert gases as a means of asphyxia has become a known practice only fairly recently. The first public discussion of inert gases as a means to commit suicide seems to have been at a 1999 conference of the Self Deliverance New Technology Group, with detailed instructions published three years later in the third edition of Final Exit (1). The usual method recommended by various sources is to feed a tube from the gas source into a bag secured over the victim’s head, although some internet sources recommend use of a breathing mask. Helium is generally recommended as the “ideal” gas for suicide by asphyxia both because of its easy availability in party balloon kits and its low narcotic and hallucinogenic potential relative to other inert gases (2). Despite this fact, there are only a handful of cases of deliberate helium asphyxia reported in the medicolegal literature (3 –8). In all but one of these reports, the cause of death was determined from physical evidence found at the site of death and/or physical findings from autopsy without supporting toxicological data. Auwaerter et al. (3) reported analysis of helium by headspace gas chromatography–mass spectrometry (GC–MS), but their method requires a complex procedure for sampling gas from the lungs at the time of autopsy. Yohitome et al. (9) reported GC– thermal conductivity detection (TCD) analysis for helium in a case of accidental asphyxiation requiring a similar procedure for obtaining gaseous samples at autopsy. † Materials Carrier gas grade helium was obtained from ARCET (Fredericksburg, VA), dry air was taken from the laboratory building compressed air system, and high purity nitrogen was produced in-house via a Domnick-Hunter (Gateshead, U.K.) MaxiGas system. Drug-free human whole blood was obtained from Clinical Controls International (Los Osos, CA), and deionized (DI) water was produced in-house with a Millipore (Millford, MA) Synergy reverse osmosis system. This is publication 11-17 of the Laboratory Division of the Federal Bureau of Investigation (FBI). Names of commercial manufacturers are provided for identification purposes only, and inclusion does not imply endorsement of the manufacturer, or its products or services by the FBI. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the FBI or the U.S. Government. This work was prepared as part of their official duties. Title 17 U.S.C. 105 provides that ‘Copyright protection under this title is not available for any work of the United States Government’. Title 17 U.S.C. 101 defines a United States Government work as a work prepared by an employee of the United States Government as part of that person’s official duties. Published by Oxford University Press 2012. through the electrical tape, and a second piece of electrical tape was placed over the puncture after sampling. When not under analysis, liquid samples were stored at approximately 48C, and solid samples were stored at approximately –208C. Results and Discussion Figure 1. Experimental setups for producing gas standards (A) and matrix positive controls (B). Figure 1 illustrates the process for preparation of standards and positive controls. Analytical procedure CG experiments were performed on an Agilent Technologies (Wilmington, DE) 6890-N system equipped with a 30-m  0.32-mm  12-mm J&W (Wilmington, DE) HP-molesieve capillary column. Carrier gas was high purity nitrogen at 1.0 mL/min. The oven was maintained at a constant temperature of 358C with a 10 min run time. The thermal conductivity detector was maintained at a temperature of 2508C with makeup flow of 5 mL/min and reference flow of 20 mL/min, both of high purity nitrogen. The detector was set for negative polarity operation with a 5 Hz data sampling rate. For the first reported case, a purged-packed inlet was used with a temperature of 2008C. Prior to submission of the second two cases, the instrument was converted to a split/splitless injector, also operated at 2008C, with a 2:1 split ratio. All injections were performed manually using (...truncated)