Toxicology and forensic science

Forensic toxicology identifies and quantifies substances, metabolites and markers in biological matrices in order to answer a judicial or medico-legal question. The matrix changes with the question: blood and urine for the state at the time of collection, hair for prolonged use over time, oral fluid for recent intake, and in post-mortem cases vitreous humour, bile, gastric content and organs. Expected concentrations change accordingly, from milligrams per litre for ethyl alcohol to picograms per milligram of hair for many substances of abuse. The result must survive cross-examination: it requires validated methods, a documented chain of custody, traceable reference standards and an interpretation that accounts for the matrix, the detection window and post-mortem phenomena.

Screening and confirmation: two steps with different requirements

The first step is almost always an immunoassay screen: fast, automatable, inexpensive, but presumptive by definition. The antibody recognises a class of molecules, not a single substance, and cross-reactivity produces both false positives and false negatives towards analogues outside the design of the assay.

The second step is confirmation, which must rest on a different analytical principle and deliver identification and quantification: in practice gas or liquid chromatography coupled to mass spectrometry. Identification rests on comparison with a reference standard analysed under the same conditions — retention time and ratios between diagnostic ions — and quantification on isotope dilution, with a deuterated internal standard added to the sample before extraction. Without the reference material, there is no confirmation.

Which GTFI documents govern the field in Italy

The Italian Group of Forensic Toxicologists (GTFI) draws up the reference guidelines for forensic and medico-legal toxicology assessments in Italy. The documents give indications and recommendations on the use of appropriate techniques and of analytical procedures established and shared by the scientific community, aiming at reliable and reproducible results. They are not statutes, but GTFI requires laboratories operating under legal mandate to adopt and apply them, and any departure must be justified and documented in the laboratory's Documented Procedure.

Why a traceable reference material is needed

ISO/IEC 17025:2017 requires the laboratory to use reference materials produced by competent producers, and regards producers conforming to ISO 17034:2016 as competent; that standard sets the general requirements for reference material producers and also covers certified reference materials. This is the mechanism by which a value measured in the laboratory is anchored to a documented chain of metrological traceability. In practice it translates into three operational requirements for each standard: a certificate stating purity, uncertainty and traceability of the assigned value; an identifiable batch with expiry date and storage conditions; and availability of the isotopically labelled analogue to be used as internal standard.

What CABRU can supply today

The CABRU catalogue includes analytical standards, deuterated standards and assay kits from Cayman Chemical for toxicologically relevant analytes that are not subject to restriction: medicinal drugs and their metabolites, alcohol consumption markers, urinary normalisation parameters. TO BE CONFIRMED — supply of certified reference standards of narcotic and psychotropic substances, which is subject to Italian legislation on narcotics and precursors and to customer authorisations, is not confirmed at present and must not be assumed available: the corresponding references are not included in the published catalogue. The intended use of each product likewise remains the one stated by the manufacturer in its own documentation.

The list is partial: the full range is in the product catalogue, in the biochemicals category and among the ELISA kits. To check the availability and terms of a reference, it is enough to state the code and write to CABRU.