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.