Application of 2-Aminothiazoline-4-carboxylic Acid as a Forensic Marker of Cyanide Exposure

Simultaneous quantification of 2-aminothiazoline-4-carboxylic acid and 2-aminothiazoline-4-oxoaminoethanoic acid utilizing chemical derivatization followed by liquid chromatography-tandem mass spectrometry

Detecting cyanide compounds in postmortem blood samples is an important matter in forensic science because cyanide is often used as a poison for murder or suicide. However, the direct analysis of cyanide itself has practical limitations because of cyanide's volatility and short half-life at ambient temperature. Here, we focused on the relatively stable cyanide metabolites 2-aminothiazoline-4-carboxylic acid (ATCA) and 2-aminothiazoline-4-oxoaminoethanoic acid (ATOEA) as potential markers of cyanide exposure. We developed an analytical method that uses chemical derivatization of the target compounds with 4-bromoethyl-7-methoxycoumarin followed by liquid chromatography coupled with electrospray ionization-tandem mass spectrometry. The recovery rates for pretreatment and calibration curve linearities were good in the concentration range of 20-1000 ng/mL. Using our approach, we were able to detect and quantify both ATCA and ATOEA concentrations in postmortem blood samples, and in our samples the ratio of ATCA and ATOEA was in the range of 4.5-19.1. To our knowledge, this is the first time ATOEA has been successfully detected in human blood samples. In addition, we found that ATCA and ATOEA concentrations were both significantly higher in the blood of fire victims than in the blood of individuals with a non-fire-related cause of death. Also, we found that there was a significant positive correlation between ATCA concentrations and ATOEA concentrations. Together, our present data suggested that ATCA and ATOEA are both potential markers of cyanide exposure.

The stability of cyanide in human biological samples. A systematic review, meta-analysis and determination of cyanide (GC-QqQ-MS/MS) in an authentic casework 7 years after fatal intoxication

A 30 year old man was found with no signs of life in front of the house. The cyanide concentration in blood and urine was determined five years after the man's death. What is more, a stability study was conducted for 730 days in an authentic casework blood sample. Sample preparation procedure included precipitation with methanol:water mixture, solid phase extraction (SPE) and derivatization with the use of PFB-Br (pentafluorobenzyl bromide). The sample was analyzed using GC-QqQ-MS/MS (gas chromatopraphy coupled with tandem mass spectrometry) isotope dilution method. Separation was done using a SH-RXI-5MS column (30 m x 0.25 mm, 0.25 µm). Detection of PFB-CN and PFB-13CN was achieved using a triple-quadrupole mass spectrometer with an electron ionization (EI) ion source in multiple reaction monitoring (MRM) mode. After 5 years from the man's death, cyanide concentration was: 1900 ng/mL in blood and 500 ng/mL in urine. Stability study performed in an authentic blood sample 6 and 7 years after the man's death revealed cyanide concentrations of 1898.2 ng/mL and 1618.7 ng/mL, respectively. While spectrophotometric and colorimetric methods recorded both decrease and increase in cyanide concentration over time, newer chromatographic methods mainly indicate a decrease. The studies presented in this paper seem to confirm this trend. However, in order to interpretate the results of cyanide concentration in biological material reliably, more research is still necessary.

Quantification of cyanide metabolite 2-aminothiazoline-4-carboxylic acid in postmortem dried blood spot samples by liquid chromatography-tandem mass spectrometry

2-Aminothiazoline-4-carboxylic acid (ATCA), which is produced by the reaction of cyanide with endogenous cystine, is a promising biomarker of cyanide exposure because of its physicochemical stability. Analysis of more stable metabolite than the toxic gas itself is sometimes useful for postmortem diagnosis of gas poisoning. Here, we developed and validated an approach that uses liquid chromatography coupled with electrospray ionization-tandem mass spectrometry for quantifying ATCA in dried blood spot (DBS) samples. The linearity of the calibration curve was good in the concentration range of 20-1500 ng/mL. Our method allows for repeatable and the accurate quantification of ATCA, with intra- and inter assay coefficients of variation of below 7.8 % and below 9.3 %, respectively. In addition, the concentration of ATCA in DBSs remained stable for at least one month when stored at -20°C. Our results indicated that our analytical approach can be used to determine past exposure to higher doses of cyanide. In a comparison of ATCA concentrations in DBSs obtained from cadavers with various causes of death, significantly higher ATCA concentrations were observed in fire victims than in non-fire victims, confirming that fire victims inhale large amounts of cyanide gas. Thus, here we extended the possible uses of DBS for quantification of ATCA to forensic toxicological testing for cyanide poisoning.

Quantification of 2-aminothiazoline-4-carboxylic acid as a reliable marker of cyanide exposure using chemical derivatization followed by liquid chromatography-tandem mass spectrometry

In this research, we have developed a novel and simple liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method for quantification of 2-aminothiazoline-4-carboxylic acid (ATCA), which is produced by the direct reaction of cyanide (CN) with endogenous cystine. In forensic science, detection of CN is important because CN is a poison that is often used for murder or suicide, in addition to being produced by the thermal decomposition of natural or synthetic materials. However, because CN disappears rapidly from body tissue, ATCA is thought to be a more reliable indicator of CN exposure. For the method reported herein, human blood samples (20 μL) were subjected to protein precipitation followed by derivatization with 4-bromoethyl-7-methoxycoumarin. Blood spiked with ATCA at concentrations ranging from 50 to 1500 ng/mL was used to prepare a calibration curve (lower limit of quantification; 50 ng/mL, lower limit of detection; 25 ng/mL). Our method uses chemical derivatization, so unlike previously reported methods, it does not require tedious pretreatment procedures, hydrophilic interaction liquid chromatography columns, or specialized equipment. In addition, our method allows for repeatable and accurate quantification of ATCA, with intra- and inter-assay coefficients of variation of below 5.0% and below 6.0%, respectively. We used the method to analyze ATCA in postmortem human blood samples, including samples from people who had intentionally ingested CN or were fire victims. Blood ATCA concentrations were higher among people who had ingested CN or were fire victims than among people in a control group (P < 0.0001). The data reported herein demonstrate that our LC/ESI-MS/MS method can be used to detect and quantify ATCA in postmortem blood samples and that CN exposure strongly affects ATCA concentration, providing a useful tool for detection of CN poisoning.

Performance comparison between solid phase extraction and magnetic carbon nanotubes facilitated dispersive-micro solid phase extractions (Mag-CNTs/d-µSPE) of a cyanide metabolite in biological samples using GC–MS

Dispersive-micro solid phase extraction (d-µSPE) has gained increasing attention due to its convenience, effectiveness, and flexibility for sorbent selection. Among a various selection of materials, magnetic carbon nanotubes (Mag-CNTs) is a promising d-µSPE sorbent with excellent separation efficiency in addition to its high surface area and adsorption capability. In this work, two different surface-modified Mag-CNTs, Mag-CNTs-COOH and Mag-CNTs-SO3H, were developed to facilitate d-µSPE (Mag-CNTs/d-µSPE). The cyanide metabolite, 2-aminothiazoline-4-carboxylic acid (ATCA), was selected to evaluate their extraction performance using gas chromatography–mass spectrometry (GC–MS) analysis. The Mag-CNTs-COOH enabled a one-step derivatization/desorption approach in the workflow; therefore, a better overall performance was achieved. Compared to the Mag-CNTs-SO3H/d-µSPE and SPE workflow, the one-step desorption/derivatization approach improved the overall extraction efficiency and reduced solvent consumption and waste production. Both Mag-CNTs/d-µSPE workflows were validated according to ANSI/ASB 036 guidelines and showed excellent analytical performances. The limit of detection (LOD) and limit of quantitation (LOQ) of ATCA in synthetic urine were 5 and 10 ng/mL, respectively, and that in bovine blood were achieved at 10 and 60 ng/mL. The SPE method’s LOD and LOQ were also determined at 1 and 25 ng/mL in bovine blood samples. The Mag-CNTs/d-µSPE methods demonstrated great potential to extract polar and ionic metabolites from biological matrices. The extraction processes of ATCA described in this work can provide an easier-to-adopt procedure for potential routine forensic testing of the stable biomarker in cyanide poisoning cases, particularly for those cases where the cyanide detection window has passed.

RECiQ: A Rapid and Easy Method for Determining Cyanide Intoxication by Cyanide and 2-Aminothiazoline-4-carboxylic Acid Quantification in the Human Blood Using Probe Electrospray Ionization Tandem Mass Spectrometry

In this study, we developed a rapid and easy method to determine cyanide (CN) intoxication by quantification of CN and 2-aminothiazoline-4-carboxylic acid (ATCA), which is a new and reliable indicator of CN exposure, in the human blood using probe electrospray ionization tandem mass spectrometry (PESI/MS/MS) named RECiQ. For CN, we applied the previously reported one-pot derivatization method using 2,3-naphthalenedialdehyde and taurine, which can directly derivatize CN in the blood. The analytical conditions of the CN derivatization were optimized as a 10 min reaction time at room temperature. In contrast, ATCA could be directly detected in the blood by PESI/MS/MS. We developed quantitative methods for the derivatized CN and ATCA using an internal standard method and validated them using quality control samples, demonstrating that the linearities of each calibration curve were greater than 0.995, and intra- and interday precisions and accuracies were 5.1-15 and 1.1-14%, respectively. Moreover, the lower limit of detections for CN and ATCA were 42 and 43 ng/mL, respectively. Finally, we applied RECiQ to three postmortem blood specimens obtained from victims of fire incidents, which resulted in the successful quantification of CN and ATCA in all samples. As PESI/MS/MS can be completed within 0.5 min, and the sample volume requirement of RECiQ is only 2 μL of blood, these methods are useful not only for the rapid determination of CN exposure but also for the estimation of the CN intoxication levels during an autopsy.

Development of magnetic carbon nanotubes for dispersive micro solid phase extraction of the cyanide metabolite, 2-aminothiazoline-4-carboxylic acid, in biological samples

2-aminothiazoline-4-carboxylic acid (ATCA) is a minor metabolite of cyanide and is suggested to be a promising biomarker for cyanide exposure due to its specificity to cyanide metabolism and its excellent short- and long-term stability during storage. In this study, magnetic carbon nanotubes, including magnetic multi-walled carbon nanotubes (Mag-MWCNT) and magnetic single-walled carbon nanotubes (Mag-SWCNT) were synthesized as a novel sorbent for dispersive micro solid phase extraction (d-μSPE) to extract ATCA from biological matrices. ATCA spiked deionized water samples with the addition of the isotopic internal standard (ATCA - ¹³C, ¹⁵N) were subjected to Mag-CNT/d-μSPE to confirm extraction efficiency of this new technique. The extracted ATCA was derivatized and quantitated using gas chromatography/mass spectrometry (GC/MS) analysis. The extraction parameters were optimized and a detection limits of 15 and 25 ng/mL were obtained for synthetic urine and bovine blood respectively with a linear dynamic range of 30-1000 ng/mL. The optimized Mag-CNT/d-μSPE method facilitated efficient extraction of ATCA using 2 mg of Mag-MWCNT with a 10-minute extraction time. The current assay was also found to be effective for the extraction of ATCA with average recoveries of 97.7 ± 4.0% (n = 9) and 96.5 ± 12.1% (n = 9) from synthetic urine and bovine blood respectively. The approach of using Mag-CNT to facilitate d-μSPE offered a novel alternative to extract ATCA from complex biological matrices.

Theoretical and experimental approach to hydrophilic interaction dispersive solid-phase extraction of 2-aminothiazoline-4-carboxylic acid from human post-mortem blood

In this paper, we proposed an innovative hydrophilic interaction dispersive solid-phase extraction (HI-d-SPE) protocol suitable for the isolation of the potential cyanide intoxication marker, 2-aminothiazoline-4-carboxylic acid (ATCA), from such complicated matrix as post-mortem blood. To create an optimal HI-d-SPE protocol, two sorbents were used: a molecularly imprinted polymer (MIP) and commercially available Oasis-MCX^®. The latter sorbent was identified as more recovery-efficient with higher clean-up abilities in a carefully optimized process. Computational analysis was employed to provide insight into the adsorption mechanism of the two selected sorbents. The theoretical results were in agreement with the experiment regarding the efficiency of the sorbent. HI-d-SPE was successfully applied to the analysis of ATCA in 20 post-mortem blood samples using LC-MS/MS. The analytical performance of the method was finally compared to prior existing methods, in turn revealing its superiority.