Quantification of Δ9-THC, 11-OH-THC and THCCOOH by SPE and GC-MS-MS in whole blood samples for forensic purposes

Castro, André Lobo; Tarelho, Sónia; Quintas, Maria José; Costa, Pedro; Melo, Paula; Castañera, Antonio; Dias, Mário

http://hdl.handle.net/10400.26/46381

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Introduction: Cannabis sativa represents the most frequently abused illicit drug around the world. Its abuse represents a major issue in terms of public health, not only due to its physical and psychological effects in terms of individual behaviour, but also due to consequences in terms of impairment, mainly as to driving capabilities is concerned. Detection and accurate quantification at low levels, namely for 9-THC and 11-OH-THC, seems crucial, in terms of response of a forensic toxicology laboratory to answer to legal requirements. The aim of this work considers the analytical validation for detection and quantification of 9-THC, 11-OH-THC and THCCOOH in whole blood samples, in vivo and post-mortem, for forensic purposes. Material and methods: The method included an SPE procedure with HLB OASIS® (WATERS) cartridges, derivatization with BSTFA:TMCS 99:1 (SUPELCO) and an hyphenated instrumental technique based in a GC-450 gas chromatograph coupled to a MS-300 triple quadrupole mass detector (BRUKER). Results: The procedure included a chromatographic run, with full separation of the three compounds, and the MS-MS detection was characterized by two product-ions (289 m/z ; 305 m/z), obtained from the parent-ion 371 m/z. The ion 289 was used for quantification. The respective tri-deuterated substances were used as internal standards. The validation included several parameters, as specificity/selectivity (with 0% of False Positives and False Negatives), LOD and LOQ (1 ng/mL to all compounds), linearity (1 – 100 ng/mL to all compounds), extraction recovery, carryover, inter and intra-day run precision (both under 15%), among others. Discussion: The developed method has shown to be fit to purpose, with good results in terms of increased sensibility and detection limits, due to an optimal response from the analytical equipment, based on tandem MS technology. The LOD and LOQ are compatible with reference values for positive real samples, namely applied to traffic roadside testing. This method has been applied to the laboratory routine, representing an effective improvement in terms of the lab response to legal requirements.