Atractyloside (ATR) and carboxyatractyloside (CATR) are diterpene glycosides that are responsible for the toxicity of several Asteraceae plants around the world. Mediterranean gum thistle (Atractylis gummifera L.) and Zulu impila (Callilepis laureola DC.), in particular, are notoriously poisonous and the cause of many accidental deaths, some suicides and even some murders. When a case history is not available, it is not easy to determine ATR or CATR poisoning anatomically or histologically. There is no current method for measuring the two toxins in biological samples that meet the criteria of specificity required in forensic medicine. We have endeavoured to fill this analytical gap.

Analysis was carried out using an original technique of high-performance liquid chromatography coupled with highresolution mass spectrometry detection (HPLC-HRMS). Given the singular structure of ATR and CATR, it is difficult to achieve and maintain the conditions required for their chromatographic separation and perfect ionization for the mass spectrometry. Separation was thus performed using an XTerra^® phenyl column (length: 150mm; internal diameter: 2,1mm; particle size: 3,5μm) (Waters) [Steenkamp et al., Forensic Sci Int, 2006, 163: 81–92] with a gradient mobile phase composed of acetonitrile containing 10% of isopropyl alcohol and a 5mM ammonium acetate buffer at pH=4.5. The chromatographic run time was 12.5min. Spectrometric detection was performed using a quadrupole-Orbitrap high-resolution detector (Q Exactive™; Thermo Scientific) after ionization by heated electrospray in negative-ion mode. The mass spectrometer operated in full-scan mode and targeted-MS² mode alternately. MS scans (288 – 292, 723 – 727 and 767 – 771 amu) were acquired with a mass resolution of 140000. The [M. – H]⁻ and [M – H+1]⁻ ions of ATR (725.2154 and 726.2188 amu ± 5ppm) and CATR (769.2053 and 770.2086 amu ± 5ppm) were used for quantification. The fullscan product ion spectrum of the compounds (resolution of 17500) was used to confirm the identity of the toxins. The processing of the biological sample (1mL) consisted of a protein precipitation followed by solid phase extraction on Oasis^® HLB cartridges (Waters) at pH=4.5.

The method was validated in the whole blood with between- and within-day RSD (relative standard deviation) less than 5.8% and 5.2% for ATR (accuracy between 95.9% and 98.6%) and 5.4% and 9.8% for CATR (accuracy between 92.0% and 107.4%). The calibration curves were linear for concentrations ranging from 0.17 to 200μg/L for ATR and 0.15 to 200μg/L for CATR. The detection limits were 0.066 and 0,055μg/L respectively. ATR and CATR were quantified in blood and urine samples from a non-fatal case of intoxication by A. gummifera. The concentrations were 883.1 and 119,0μg/L respectively in peripheral blood and 230.4 and 140,3mg/L in urine. ATR and CATR were quantified in dried A. gummifera roots by the standard addition method. The concentrations were 3.7 and 5,4mg/g respectively.

We present the first validated method, applicable in forensic toxicology, for quantifying ATR and CATR in whole blood. The analysis is sensitive and quick.