Fundamentals of Analytical Toxicology. Robin Whelpton

evolve hydrogen sulfide and phosphides evolve phosphine – the ability to smell hydrogen sulfide (rotten egg smell) is lost at higher concentrations

Examination using a polarizing microscope may reveal the presence of tablet or capsule debris. Starch granules used as ‘filler’ in some tablets and capsules may be identified by microscopy using crossed polarizing filters when they appear as bright grains marked with a dark Maltese cross. If distinct tablets or capsules are observed, these should be placed in individual containers. Such items and any plant remains or specimens of plants thought to have been ingested should be examined separately.

      The local poisons information service or pharmacy will normally have access to publications or other aids to the identification of legitimate and sometimes illicit tablets/capsules by weight, markings, colour, shape, and possibly other physical characteristics. Identification of such material by reference to a computerized product database may be possible.

       2.3.5 Oral fluid

      Whilst not normally considered in either emergency clinical or post-mortem work, there is much interest in the collection of oral fluid from individuals because collection is non-invasive and reflects to an extent recent drug or alcohol usage. Moreover, oral fluid collection for forensic purposes, drug-impaired driving for example, has the advantage that sampling can be carried out by suitably trained staff while the donor is under observation, hence it is more difficult to adulterate or substitute the specimen (Section 18.3.1.1). There is also interest in oral fluid collection for TDM purposes (Section 20.3.3).

      

       2.3.6 Sweat

      Sweat production is not uniform in either amount, or composition. ‘Insensible sweat’ is moisture that is lost from the body through the skin and does not form droplets. ‘Sensible sweat’, i.e. sweat that can be seen as liquid, arises from two types of gland, apocrine and eccrine. The former, which tend to be located in the axillae, pubic, and mammary areas, are larger and secrete a thicker substance. The surface of the skin is also covered with sebaceous secretions, chiefly lipids, higher concentrations being found on the scalp and forehead. Thus, the fluid collected for analysis by patches applied to the skin is generally a mixture of secretions and can only give an indication of drug exposure over the period when the device was attached to the skin.

      Collection of sweat has been suggested as a means of testing for misused drugs. Surface contamination by exposure to drug use by others (e.g. smoking either cocaine, or cannabis) is a potential problem when analysing sweat. There are two methods of collecting and testing sweat. One is the Drugwipe, which may also be used with oral fluid, and has found use for roadside testing (Section 17.3.2.1). The other is a tamper-proof ‘sticking-plaster’ that may be used to collect sweat over several days and is generally used in detoxification clinics and US prisons. The patches are not amenable to point-of-contact testing (POCT).

       2.3.7 Exhaled air

Measurement of concentrations of volatile substances in exhaled (expired) air by infra-red or other device is of course essential in roadside testing for ethanol and valuable in assessing exposure to poisons such as carbon monoxide (Chapter 17). Direct MS of exhaled air can also detect many compounds, including not only inhalational, but also i.v. anaesthetics such as propofol (Dong et al., 2017). However, the use of these techniques is limited by the need to take breath directly from live subjects. Similarly, collection of exhaled air into an impervious plastic (Tedlar^TM or PTFE) bag can facilitate the analysis of a number of substances and metabolites via subsequent GC or GC-MS analysis (Castellanos et al., 2016). Misused drugs can also be detected in exhaled air (Section 18.6).

       2.3.8 Cerebrospinal fluid

      CSF collected via needle aspiration is sometimes used to assess exposure to centrally acting drugs (Shen et al., 2004), and may be submitted for analysis if a possible drug administration error is under investigation. As with vitreous humour and synovial fluid, CSF is normally within a relatively protected environment, and thus may also provide a valuable sample for corroborative ethanol measurement, for example, in the event that other samples are not available (Tominaga et al., 2015).

       2.3.9 Vitreous humour

      Vitreous humour can sometimes be obtained even if a corpse has been extensively burnt or damaged, if putrefaction is beginning to occur, or if samples such as urine are not available (Arora et al., 2016; Metushi et al., 2016). This specimen may be especially useful when investigating diabetes-related deaths and assessing other parameters such as renal function (Belsey & Flanagan 2016). It can also be valuable for the analysis of alcohols, digoxin, lithium, and some other compounds such as insulin analogues (Ojanperä et al., 2013). Vitreous humour glucose falls rapidly after death and potassium increases even with careful sample collection and such measurements must be interpreted with due caution (Belsey & Flanagan, 2016).

      Vitreous humour is essentially a salt solution with very little protein, and thus any poisons or metabolites present can often be extracted as though they were in solution in buffer. Samples should be collected from each eye separately if possible, and sodium fluoride preservative (2 % w/v) added to one sample. Care must be taken during sampling because use of excessive suction can cause a significant change in the concentration of certain analytes and there is always the possibility of post-mortem change (Dinis-Oliviera et al., 2017). The presence of concurrent vitreous disease may also be a factor (Parsons et al., 2003).

       2.3.10 Synovial fluid

      Synovial fluid collected via needle aspiration has been used, for example, to assess the uptake of non-steroidal inflammatory drugs into their likely site of action (Day et al., 1999). As with CSF and vitreous humour, collection of synovial fluid may also be helpful in the event of traumatic death or extensive decomposition because it is located in a relatively protected environment.

       2.3.11 Pericardial fluid

      As with synovial fluid, pericardial fluid is normally within a relatively protected environment, and thus may also provide a valuable sample for drug screening or for corroborative ethanol measurement, for example, in the event that other samples are not available (Maeda et al., 2006; Tominaga et al., 2013; 2015).

       2.3.12 Intraosseous fluid

      Intraosseous fluid has also been suggested as a further specimen that may be useful if there has been extensive trauma, for example (Rodda et al., 2018).

       2.3.13 Liver

Liver is easily collected post-mortem and readily homogenized. It may contain large amounts of drugs and metabolites, and may be the primary specimen submitted for analysis if blood is not available. A portion (10–20 g) of unpreserved wet tissue should be collected. The sample should be taken from the right lobe, if possible, to reduce the risk of contamination with bile and because any diffusion of poison from the stomach is less likely than in the left lobe. An analysis may, in some cases, help to establish whether either acute, or chronic exposure has occurred, but sometimes the analysis can do little more than establish exposure in the absence of reliable information to aid in the interpretation of quantitative results (Section 22.3.2).

       2.3.14 Bile

      Bile tends to contain higher concentrations of drugs and metabolites than other body fluids and thus can be a useful specimen if blood and urine are not available, or if ingestion of a very potent poison is suspected (Bévalot et al.,