Fundamentals of Analytical Toxicology. Robin Whelpton
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Название: Fundamentals of Analytical Toxicology

Автор: Robin Whelpton

Издательство: John Wiley & Sons Limited

Жанр: Биология

Серия:

isbn: 9781119122371

isbn:

СКАЧАТЬ such as GC-MS can provide robust analyte identification, particularly when combined with computerized libraries of electron ionization (EI) fragmentation data that can be searched rapidly to confirm compound identity (Grapp et al., 2016). In addition, positive ion chemical ionization (PCI) MS can be used to give an indication of the molar mass of a substance (Section 13.3.1.2).

      The third step in STA is to compare the observed data with validated database information. Clearly, databases used in compound identification need to be regularly updated, and must include information on not only parent compounds, but also metabolites, common interferences, and possible contaminants. It is important that the analytical techniques used in establishing such databases are reproducible, both within and between laboratories.

       1.2.3 Ethanol and other volatile substances

      Enzymatic methods for plasma ethanol using alcohol dehydrogenase with spectrophotometric measurement of a coenzyme, for example, are available in kit form for clinical chemistry analyzers. GC analysis of ethanol either by direct injection of blood or urine diluted with deionized water, or by static headspace sampling (HS-GC), is also widely used, particularly in forensic work. GC-FID is advantageous because methanol, 2-propanol, and acetone may be separated and measured simultaneously. Methanol poisoning from ingestion of synthetic alcoholic drinks is one of the few causes of acute poisoning ‘epidemics’ and measurement of blood methanol is important in confirming the diagnosis and in monitoring treatment (Section 22.4.1.2). Detection of high concentrations of acetone, itself a metabolite of 2-propanol, and vice versa, may aid the diagnosis of ketoacidosis (Belsey & Flanagan, 2016).

      Many more volatile compounds may be encountered in acute poisoning arising, for example, from deliberate inhalation of vapour in order to become intoxicated [volatile substance misuse, ‘glue sniffing’, solvent abuse, inhalant abuse, volatile substance abuse (VSA)]. Some of these volatile compounds have metabolites, which may be measured in urine in order to assess exposure, notably hippuric and methylhippuric (toluric) acids (from toluene and the xylenes, respectively) and trichloroacetic acid (from trichloroethylene). However, most volatile substances are excreted unchanged in exhaled air and therefore whole blood is the best sample for detecting and identifying these compounds (Section 22.4.23).

       1.2.4 Trace elements and toxic metals

Technique Mode Variant
Electrochemical PotentiometricCoulometric Ion selective electrodes(Differential pulse) polarographyAnodic/cathodic stripping voltammetry (A/CSV)a
Spectrophotometric Optical Emission (OES) Flame emission photometry (FEP)b Direct-current plasma Inductively coupled plasma (ICP)
Atomic Absorption (AAS) FlameHydride generationElectrothermalCold vapour
X-Ray Fluorescence
Nuclear Neutron activationProton activation
Mass spectrometric Inductively coupled plasma (ICP-MS)

      aAlso known as potentiometric stripping analysis (PSA)

      bNormally refers to the use of filters to select the emission wavelength – used mainly for potassium, lithium, and sodium assay

      ICP-MS is a multi-element technique that can detect and measure isotopes with detection limits of μg L–1 to ng L–1. Different isotopes of an element can also be measured. For some elements, the relative abundance of the isotopes depends upon the source of the metal. Therefore, by measuring the isotope ratios of an element such as lead in a sample from a chronically poisoned patient with those found in material present in the patient's immediate environment it may be possible to localize the source of exposure (Gulson, 2008).

Pre-analytical Obtain details of the current (suspected) poisoning episode, including any circumstantial evidence of poisoning, and the results of biochemical and haematological investigations, if any. Also obtain the СКАЧАТЬ