Alternative matrices in forensic toxicology: a critical review

Abstract

Purpose The use of alternative matrices in toxicological analyses has been on the rise in clinical and forensic settings. Specimens alternative to blood and urine are useful in providing additional information regarding drug exposure and analytical benefits. The goal of this paper is to present a critical review on the most recent literature regarding the application of six common alternative matrices, i.e., oral fluid, hair, sweat, meconium, breast milk and vitreous humor in forensic toxicology. Methods The recent literature have been searched and reviewed for the characteristics, advantages and limitations of oral fluid, hair, sweat, meconium, breast milk and vitreous humor and its applications in the analysis of traditional drugs of abuse and novel psychoactive substances (NPS). Results This paper outlines the properties of six biological matrices that have been used in forensic analyses, as alternatives to whole blood and urine specimens. Each of this matrix has benefits in regards to sampling, extraction, detection window, typical drug levels and other aspects. However, theses matrices have also limitations such as limited incorporation of drugs (according to physical–chemical properties), impossibility to correlate the concentrations for effects, low levels of xenobiotics and ultimately the need for more sensitive analysis. For more traditional drugs of abuse (e.g., cocaine and amphetamines), there are already data available on the detection in alternative matrices. However, data on the determination of emerging drugs such as the NPS in alternative biological matrices are more limited. Conclusions Alternative biological fluids are important specimens in forensic toxicology. These matrices have been increasingly reported over the years, and this dynamic will probably continue in the future, especially considering their inherent advantages and the possibility to be used when blood or urine are unavailable. However, one should be aware that these matrices have limitations and particular properties, and the findings obtained from the analysis of these specimens may vary according to the type of matrix. As a potential perspective in forensic toxicology, the topic of alternative matrices will be continuously explored, especially emphasizing NPS.

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“…Biological matrices such as sweat, hair and saliva are alternative samples for determining an individual's exposure to certain drugs or other chemicals. Their advantage is non-invasiveness, painless collection compared to blood collection, but due to the smaller number of published data, especially in terms of assessing the effects of physiological and psychological status, they still remain only alternative matrices in practice [42,45]. In the case of sweat and hair, the preference lies in the possibility of detecting certain drugs and medicines even after a longer period of time, in contrast to blood [46,47].…”

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“…On the other hand, this matrix can be variable, being influenced by factors such as circadian rhythm, age, gender, and health, among others. From an analytical perspective, the sample volume is generally limited, and analytes may be present in low amounts, requiring highly sensitive detection methods (de Campos et al 2021 ). Additionally, hair analysis can be used to detect the presence of drugs and some metabolites.…”

“…While it is still unclear exactly how drugs are incorporated into the hair, it is generally accepted that it involves passive diffusion through blood capillaries to the base of the hair follicle (Mantinieks et al 2018 ). Similar to oral fluid, the collection of hair samples is easy and non-invasive and can help provide a timeline of drug use through segmental analysis; however, the detection of recent drug use (within approximately 7 days) is not possible (de Campos et al 2021 ).…”

“…In addition to hair and oral fluid, a number of other unconventional matrices have been reviewed in the literature, including sweat and vitreous humor (de Campos et al 2021 ), bile (Bévalot et al 2016 ), nails (Solimini et al 2017 ), bone marrow (Cartiser et al 2011 ), and cerumen (ear wax) (Meier et al 2017 ). The use of human breast milk and meconium, the first stool excreted by a newborn, has also been investigated in order to identify licit and illicit drug use by mothers during pregnancy (de Campos et al 2021 ).…”

“…In addition to hair and oral fluid, a number of other unconventional matrices have been reviewed in the literature, including sweat and vitreous humor (de Campos et al 2021 ), bile (Bévalot et al 2016 ), nails (Solimini et al 2017 ), bone marrow (Cartiser et al 2011 ), and cerumen (ear wax) (Meier et al 2017 ). The use of human breast milk and meconium, the first stool excreted by a newborn, has also been investigated in order to identify licit and illicit drug use by mothers during pregnancy (de Campos et al 2021 ). While each of these matrices have unique advantages and disadvantages, it is important for an analyst to select the most appropriate matrix for the case under investigation and alternative matrices can be useful in situations where blood and/or urine is not available.…”