A highly sensitive headspace gas chromatographic method fully optimized for fast routine determination of carboxyhemoglobin in postmortem blood

Abstract

In some cases, the determination of carboxyhemoglobin (COHb) concentration in postmortem blood using standard spectrophotometric methods, may be either impossible or yield misleading results. In forensic laboratories, there is an increasing need to analyze COHb saturation in autopsy blood samples, the quality of which is often compromised by various factors. Therefore, a gas chromatographic method has been developed and validated to confirm the results of an established spectrophotometric method and to determine the concentration of COHb in postmortem samples affected by processes such as putrefaction or thermocoagulation. This method is based on automated headspace analysis of a blood sample treated with a solution of potassium hexacyanoferrate and saponin. It employs a combination of two capillary columns for chromatographic separation, followed by a highly sensitive detection system that incorporates a methanizer to convert carbon monoxide (CO) to methane couple to a flame ionization detector. The percentage of COHb concentration is calculated using the ratio of the analyzed blood to that of fully CO-saturated blood. Careful optimization of the method has reduced the sample requirement to 100 mg while maintaining high sensitivity. Additionally, the sample pretreatment process has been simplified to ensure that the method can be easily integrated into the routine operation of a conventional forensic laboratory. The method demonstrates linearity across a concentration range of 0.1% to 100% COHb. The determined values of limit of detection (<0.01% COHb) and limit of quantification (0.1% COHb) reflect excellent sensitivity. Overall, the validation study confirmed the method for its intended purpose. The method is particularly effective in reliably determining COHb content in putrefied and similarly degraded samples. Its robustness has been further validated through the analysis of dozens of real samples over more than 4 years.